Episode: 4019
Title: HPR4019: Fairy lights and Powerful Pixies
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr4019/hpr4019.mp3
Transcribed: 2025-10-25 18:43:28

---

This is Hacker Public Radio episode 4,019 for Thursday, the 28th of December 2023.
Today's show is entitled Fairy Lights and Powerful Pixies.
It is hosted by Ken Fallon and is about 78 minutes long.
It carries a clean flag.
The summary is, Ken is visited by the Ghost of Procrastination, Desperation and Rambling.
Hi everybody.
My name is Ken Fallon and you're listening to another episode of Hacker Public Radio.
I'm recording this on Christmas Eve 2023.
I started my first edit of this or first attempt to record this nearly two years ago,
at which time I drew the diagrams that I'm going to be possibly referring to on the whiteboard.
I need to do it tonight and I'm doing it slightly differently to normally do,
but I just recording it as I go along in Audacity.
I'm going to do a truncated silence, but other than that, I'm not going to do anything more.
The reason I need to do this is that I need to see Christmas for somebody.
Somebody, one member of the family has some fairy lights,
you know, cheap ones that you get in the action over here,
just like a pan store or something, and they run off two batteries
and I want to convert it so that you can plug it into a USB,
charred into a USB wall wart thing.
So that's the reason it needs to be done tonight.
Got some tea. Roy Boss, if you're interested.
As I said, I'm recording this just in Audacity.
Stream of consciousness. We'll see how it goes on as I go along.
I've tried recording this many times. They've all failed.
I guess he's by the ghost of procrastination on Christmas Eve.
What could be more Hacker-y than that?
So, I'm down here in my office basement,
where the washing is, and where I work normally,
and I have here in the bag.
This is actually this fairy light thing
only broke recently as in this year,
so I said I would fix it for them this year.
But the show itself has been on the board for a while
because I have converted already a lot of Christmas lights
to use AC power, so I don't have to go around
and change the batteries.
So, yes, you can say thank you very much Ken.
By the time this comes out, it will be the 27th,
and you will too late for Christmas,
or, or, the other way of looking at it is,
that you are perfectly in time for next Christmas.
So, you have the maximum amount of time between now and Christmas,
2024, to get all your lights converted.
So, actually, this is a good little project to do
before you put all the Christmas decorations away.
And it used to really drive me nuts,
going around every evening, turning off the power at all,
the little Christmas village that I got, I got.
So, I already did a show about converting that.
So, okay, as you can tell, I'm trying to push,
put off doing this show.
So, this LED light thing, let me actually put it into here.
So, I've got a plastic carton.
It's an ejection PTFE, there's a PTFE.
No polypropylene.
See through jar, that they have Yodoku,
translates as Jewish cookies.
And they're immensely durable there, about like, let's see.
Six inches high, or 160 members,
by four inches wide, 10 centimeters.
Very durable, like, you know, copy,
plastic beaker type thing.
So, what I'll do is I'll put the lights in there for say,
keeping it also making that effect.
The string is of, you know what?
I could take a photo, did I have?
Canada, yep.
That's, uh, why do these up?
They're currently strung out,
because they went into a bit of a bowl.
So, I'll roll them up, kind of carefully, and pop them into this container.
Then I'll take one photo.
I don't want to be doing too many photos or devil go nuts.
Now they're in turn not again.
Which is a nice effect himself, but not what I'm going for right now.
Okay, stuff them in there.
And I'll take the photo of that.
So, two photos taken.
Well, we have here our little
few moments later, actually quite a few moments later,
and I was talking to the person I'm doing this for.
So, um, yeah, this thing has got two wires running down and about,
let's see.
And every 10 centimeters, four inches, there's a plastic injection molded star.
That's why it's injected with most transparent, injected injection molded plastic item.
I'm just looking here on the magnifying glass, and joining between the two
is a little LED light, let's be kind of lights up on my desk, LED.
Now, to the better look at it.
And it looks like it's just a surface mounted LED light that is, yeah, surface mounted LED,
um, surface mounted LED that's joining the two wires in parallel.
So, you got a top wire and a bottom wire and all along, you've got small little square
LEDs that you will find on a flat printed circuit board attached, and then they probably put
the wire insulation on afterwards, flooded the whole thing. So, kind of nice, nice effect.
So, what does that tell us?
They're caught here, um, they basically broke off.
They are 40 LED pairs in that bunch, and then they come down to a battery pack, and the battery
pack has an all-enough button. It's quite a nice little battery pack, and the name of the
brand is Sirius. It is conforming to EU regulations because it's got a screw.
That's interesting. It's got a screw over the battery pack so that it can't be opened by kids.
However, if you just push back the tab, it opens. Fantastic, a little bit.
Okay, now, what I'm seeing here are two batteries, yeah. I'm not going to say anything about what
type of batteries there are, as yet. So, what we have here is an opportunity to discuss
AC, DC electricity, voltages, current, power, all that sort of stuff, even ohms low, and
power calculations. So, don't get freaked out. It's easy enough to follow along.
And this project, by the way, I just happen to be repairing this and converting it from
battery pack to a wall wart. But you don't need, I'll be using a solder here, soldering iron,
you don't need soldering iron. You can just do this, twist the wires, put some cello tape,
double-sided sticky back plastic, as he used to say, on blue Peter on the BBC.
And that's close enough for jazz, yeah. When you're doing that, if you're joining ever two wires,
you don't want the positive and the negative to touch. You don't want the two wires to cross
because then a lot of electricity flows between the two. So, if you're doing that sort of trick,
where you're joining with the elastic tape, make the cuts so that they're not together.
Leave an inch or five, two and a half centimeters in between the joints. So, cut the top one,
the top one, long and short, and cut the bottom one short and long, and then they're offset.
So you can solder tape to get them together, that if one of the wires sticks out to the sold tape,
it hits the insulation of the other strand rather than the on-insulated, rather than a little wire
if it comes out on the other side. So, that's a little tip. All this entire thing can be done
without soldering iron or tools. So basically, that's all we need. Now, your battery pack,
you're not going to go down to the pound store, dollar store, and pick up
or your store, I guess, your store, not to be confused with your train that goes from
the condo notes to the UK. So, you've got the pack and these battery packs, you need to be able to open
them. So, you open the battery pack, this thing number one, and you take out whatever batteries happen
to be in there. I did a show on batteries earlier, but we'll continue on. Now, typical battery pack
has got a spring on one side, and on the other side there's a piece of flap metal, and then the
other compartment has got a spring, and on the other side there's a piece of flap metal. So that's
this one. However, over here I've got a bag of these little projects that still need to be done,
and I could examine the battery packs of some of these other ones. Here, this one here. This one
here has got three of those plastic things in it. So, three different compartments. So, they,
but in all of them, the spring car responds with a flap piece. The flap piece connected to another
piece that's got a spring, then back to the other side. It's got a flap piece, a flap piece
connected to one with a spring, and the spring connects to the flap piece of the back. So,
what's going on here? Very interesting, very interesting. So, that one will keep out, and then
the other ones are just variations of other spring compartments or two compartments. So, interesting.
It's like we're investigating a crime here, but we are actually investigating. We're trying to
figure out several different things. So, we know that this is direct current, because that's
what a battery provides. So, what does that mean? Well, one of the reasons for the show getting
delayed so long is that if you ask that question, it leads to a huge big rabbit hole ending up with
lots and lots of answers. So, let's avoid all those for now, and just assume that you have all
electrons, little pixies, as Big Clive says, one of the YouTubers I follow to learn this stuff.
They're all lined up in a row, right? And they're queuing up for Santa, yeah? And as one steps forward,
the next steps forward, and as the other one steps forward, the next steps forward. And they're going
actually really, really slow, like, yeah, but they are going in that direction, really, really so.
But as soon as they start walking, they lean forward, hitting the next guy, and the next guy,
and the next guy, as you might do, just kind of tripping like that. And that causes what's called a
wave, not a physical thing, but a movement, that movement, like you walk or you run, there's a wave
that travels down the line and comes out the end. That's as good an explanation
of what's happening with electricity that you're going to hear on the show today.
Okay, so that's that. Now, you tell me, okay, how can a wave go faster than the thing that's on? Well,
if you're at the seaside, and you see the waves coming in, the water's staying in the same place,
it's just going up and down and up and down, but the wave itself is the movement of the water
going across. Think of it like this, if you've ever seen the football stadiums during a
World Cup match, where they do the Mexican wave, and it goes around the stadium, the wave does,
the movement does, but the actual people stay seated in their seat, they do move a little bit
up and down, but they don't move along with the wave. That's enough about that. Now, can you imagine
if these angry pixies are standing in the line, waiting for Santa, right? And they're so close
together that if at the end of the line one center, one of Santa's elves was pushing the pixies to
the left, and then what do we call them? Grinch is on the other side pushing them back, so when they
can push one side, they push back, push the other side, they'll push back. That's all related,
just, it's Christmas Eve, give me a break. Okay,
somebody starts a career in a fun experience on this show, that image would be stuck in the head
forever. Okay, that's all related, current, basically pushing two and four. The pixies in the middle
stay more or less the same way, the move a little bit to the left, a little bit to the right,
but the movement is done very fast. So, faster, in fact, almost the speed of light. Actually,
the speed of light, as it turns out, but it's slowed down by the dielectric, said as if he understood
what that meant. Okay, we now know what AC current is, we now know what DC current is. One thing to
remember is that these little pixies all under all don't like you and they don't like your equipment
and they're out to break it and turn it into, to release the magic smoke here. So, you have to
be careful with it, even with DC. And during this entire series, we're going to be talking about AC,
but we're not going to be messing with it, and you're not going to be taking measurements with it,
and you're not going to be cutting wires with DC, with AC, and the AC stuff is this stuff coming from
the power outlet, yeah. So, you're not going to be messing with that stuff. Even with DC stuff,
that you get from lithium ion battery packs that you might have converted from
a interchargers, from recycled batteries, from laptops, you're not going to be messing with
that stuff either. We're going to be messing with the nice, boring, cheap batteries area,
and any of the, any of the electricity stuff to do with the mains voltage, that stuff will kill
you in an instant. I'm not care. And we can continue to kill you, yeah. So, no messing with AC
for now, at least. Where was I? Oh yeah, looking at a battery, right? Let's have a look.
I'll grab my magnifying glass, bring it over to the life, what does it say? Says AA batteries.
All right, well, let's have a look at what Wikipedia says about AA batteries.
Hashtag. Exclamation mark, AA battery. And that brings us to Wikipedia. The AA battery,
or AA battery, is a standard size of single cell dry battery. What's a dry battery, you ask?
Now, that is important. It is a dry cell as the type of electric battery commonly used for
portable devices, unlike wet cell batteries, which has a liquid electrolyte. Dry cells use
electrolytes in the form of paste, and thus less susceptible to leakage. So, these are electrochemical
devices. And what happens is, when you join one side to the other, a chemical reaction occurs
that releases electricity, makes those pixies want to want to walk up to sand day, yeah. Super.
So, we've got a plus on one side, and we've got a minus on the other side. And what that actually
means is the opposite of what you think it means, because they, when they came up with this, the
the toss, the electrons flowed in a different way. I'm going to say electrons and pixies,
they're interchangeable. So, when the electrons flow, they actually go out the minus and come back
to the plus, but by the time they discovered that piece of information, it was too late,
and it's actually for the most part, it doesn't really matter. So, we follow electrical convention
here. So, the pixies, the electricity flows, and you think it goes out the plus and comes back
to the minus, well, at least the holes do. Okay, what else can we see in this? We can see something
that says, I don't know, A, it's an aerosol, 1124, it's made in Germany, and that's a whole lot
of use to me. And it says something 1.5 volts, 1.5 V, what's that? Well, that is interesting.
Volt in Wikipedia. So, a volt symbol V is used as a unit of electrical potential and
electromotiv force in this IS standard units. One volt is defined as the electrical potential
between two points on the conducting wire when the electricity of the current of one ampere
dissipates one watt of power between the two points. Woo! Couldn't have said it better myself.
What it means is how strong the pixies are. So, yeah, it's pretty much it. You will hear many other
definitions in your life, but that's the one that's hopefully what stick with you. How strong
the pixies are. Some people describe it as, say, you've got water flowing. If we use the flow of water
to describe electricity as an analogy for electricity, it's the head of water, how high it
operatives. So, the higher up the water, the more electrical, the more potential energy
have that will fall down. The lower down, the less, umph it's got. But we're going to think how
pumped our pixies are here. Okay, so does that tell me then how much, so if I put these batteries
back, right? The first thing we're going to do is I'm going to take my LEDM or my voltmeter,
digital voltmeter. It's actually a multi meter and that's really cheap and I'm going to check
the voltages. So, turn it on and I switch it to continuity. It beeps and then I switch it to V.
Now, I've got several V's of mine. One V has got two horizontal lines. One is solid and underneath
that are like three dots. So, a bit like the hamburger menu except the top line is solid.
And then, underneath that, there's another section for V with a squiggly line. A bit like a wave.
So, one stands for is a symbol for direct current and the other one is a symbol for alternating
current. And the reason that it's a wavy line is because AC is generated using generators. So,
like a turbine, like a water turbine in a dam where a flow of water goes down, spins the turbine
generates electricity or in a wind turbine where the blades of the motor turns and the turning
of that generates electricity. And, for example, gas turbines for the e-top, where the use gas
to eat a water to turn it into steam high pressure goes and turns a turbine which turns a motor
which turns magnets which generates alternating electricity. Why is it alternating if it's spinning
you ask? Well, imagine you've got a bicycle going around, going around and attached to the
bicycle, hypothetically, you have a marker and the marker is pointing out the side of your
attach it in the spokes so that it's pointing out as you spin around, ignore the fact that it has
to go through the spokes here for a minute but it spins around in a circle. And if you were to go to a
OK, so I'm going to set us to DC. We're going to take the batteries and check each of the batteries
first and put the black onto the bottom which is minus. Black is traditionally known as
negative and put the red to the top which is positive. This battery is reading one volt which
means it's dead as a door nail. So I'm going to get fresh batteries for the purposes of testing this.
OK, two new batteries have been acquired. So 1.6 volts. So it should be normally, it should be
normally around 1.5 but when this one is 1.6, 1 volts. But when you put them under load
they will get stressed out more. OK, so we know that both of those batteries are more or less
around 1.5 volts. So we've got two of them. Now there's two weights to wire up batteries. You can
either wear them in parallel or in series. So think of your pixies and you got two pixies. Both of them
are 1.5 on the pixie scale of strength and you are now going to have them do stuff. So you have
two options. They have to move the cart for Santa with presents. So you can either push,
have them line up behind the cart. So you put the first pixie behind the cart and that pixie
starts pushing the cart. This analogy is going to fail but we will carry on. So if you push
the pixie pushing, so there's the same amount of power available. Because you've got essentially
two pixies. So there's the same amount of energy there. So you can push them behind one pixie's
pushing the cart and the weighing scales on the cart. If you're pushing weighing scales attached
to the cart, it would show 1.5. But if you put another one behind and both of them are pushing
against that weighing scales, you would have three showing up on the weighing scales. So the power
of three pixies are vaults as we call. However, if you had two weighing scales side by side in the
back of the cart and you had two pixies pushing on the weighing scales, you would see that both weighing
scales showed 1.5. So if you put the pixies in parallel, you get 1.5 but you can continue for
double amount of time. If you put them behind each other, you get doubled the voltage but they
will only last as long as similar length of time. That's a bad analogy. But take another glass
of mold wine and we will continue on. Right, let's have a look here. I'm going to use another
multi meter which I'm not going to use now because the thing is just broken off.
This is what's happening with the show the whole time as I do it. I've fitted those and what I need
to know is how much voltage is going to come out of this thing when I turn it off. Now I can guess,
I can study and figure it out or I can measure it. So I'm going to figure it out and see. So I've got
the first battery. I'll put that in to the compartment and I put, it's, I look at it and it's
got a plus and a minus and I look at the battery and the battery's got a plus on one side and a
minus on the other. So I put the minus which is the bomb, the black part of the durosol battery
in and the plus is the gold side of the durosol battery. Now I'm going to take those out again.
Actually I'm going to put my multi meter to continuous mold so that if the two, if a current,
if electricity pixies are able to get from one side to the other side, you'll hear a beep like
that. So what I'm doing is I'm now putting one connector onto the spring on one side
and one connector onto the spring on the other side. Those are not connected. However, at the bottom
of the battery compartment, I can see that there's a spring and a piece of flat in there. So there's
going to be a positive connecting and a negative connection coming in here. So I'm going to turn
those joined together. I think they are because you can see it, but to be sure I'm going to check
with my multi meter. Yes, sure enough, the bottoms are connected. What does that tell us? Interesting,
sure enough. Okay, so taking out my durosol battery here again, doesn't have to be durosol, but
I just happen to have them. I bought the black base where it says minus and then I put the
plus which is marked on the battery into the connector where it says plus. Now the plus goes to
the end of the battery compartment and there's a piece of metal from the left hand side to the right
and on the right hand side it goes from the flat to a spring and that has got minus on it. So I
connect the black part to the minus of the durosol battery in there and I put the plus in and now I can
see that the pixies, if they want to get from one side, one wire to the other at the top, they need
to go down the battery to the bottom, cross over and come back. So that would be two of our pixies
pushing together. So I reckon that's 1.5 plus 1.5. So together, if I put these wires together,
it would look like I have a pixie who is as strong as three pixies. So three volts. So let me
change my multimeter back to volts, turn it to volts 20 to zero on the DC line and then I connect
either pain and doesn't really matter to one side and connect to the red to the other side and
I'm getting zero volts. Now reasons for that because it's not turned on. So let's turn it on
and do that again. I put the red to one side and then I connect the black lead of my multimeter
to the other side and I'm getting also nothing. Why is that? Interestinger and interestinger.
So I'll turn it off just to be on the safe side and take out the batteries again.
So now we're into the realm of trouble shooting and we're also into the realm of why this
should take so long or something that's really rather simple. And this could very well be
that there's insulation still on the wire. So where broke off, the wire is not exposed. All
them access able to access possibly. This is possibly I'm guessing here. All that I'm able to
access is the insulation that has been added to the front of the wire and not the wire itself.
So I'm taking my wire strippers and I'm going to try and clear off the insulation on the wire.
It could be quite hard to do because if it's painted on and you know some wire it's a plastic molding
and it's easy enough to take it off. But if it's actually epoxy or something that's put on top
then it's basically a paint that's on there. The only way to get rid of it actually is to
what I'm going to do now is scrape it off. So I'm going to bring that over to my
causing mat and hold it down and then try and hold in the wire. Take if you
hold in the wire flat on the ground, fixed with my hand, taking a very blunt
blade on knife and scraping the last probably a centimeter or once that's in metric or in imperial
about quarter of an inch or half a centimeter of just scraping away half a centimeter from the back,
half a centimeter back to the front of the wire and do that trying to get the insulation off.
I'll try and turn it around and repeat that process and I can kind of feel the plastic
fighting me on it. But we can't see it even with a magnifying glass. Let's see here.
Yeah, it's ugly. It's all sorts of, you can see the cable and the copper strands of the cable
and on that we have sort of a plastic dental for the best work to describe it, I guess.
We have a look at it. Is that up? Is our hand good? I don't know. I can't believe it to get some
emery paper or not why it's called emery paper. Somebody knows. Do you show?
Yeah, that one's done. I can feel at least a little bit of wire, you know, a little bit the
braid of the copper on it. The correct thing to do now will be go to the shed, kind of cold
winter's night and get some sand paper at home. Not in the mood to do that.
Which should probably end up having to do that anyway in the end. So that at least feels like
I've got contact. Another thing some people do is burn it off. Let's see if that trick will work here.
So I will do a little bit to make this door.
My soldering box, and in there I've got a kitchen tube and a small silver organizer.
So did that work. So I tried to, yep, that burnt it off. It's a bit ugly.
A lot of people use a soldered heated soldering iron for this. So let's see if we have contact.
Now, one way to check that is with my continuity and reader. Again, my voltmeter
take it out, put it into continuity mode, switch the dial over so that if there's a connection,
I should hear. So now I'm checking the spring at the top and the issue is I want to know which
one is connected, whether it's positive or negative. So neither of them, I'm holding the wire on one
side and it is not making a beep for either of them, which is not good. And I'm holding a wire
to the other side. It's also not making a beep, which is also not good. There is exposed wire there
because I'm hearing it. So what's going on here? I've just noticed that there's a connector.
Slightly down from the battery pack is a some sort of device. It could be a connection point.
Maybe that's done wrong. Anyway, forget all that. This is typical troubleshooting. This is why the
takes so long. What we do is we put the batteries back in because we're not going to be using this
compartment. We line them up and I will simply just attach the probes directly into the
back to compartment and then we can get a reading. So when I put my probes in, I'm getting a reading
of 3.23 volts. 3.23 volts. Wow. That was a lot of work for very just for results that we could see
and we calculated already earlier. Now, just for the fun of it, what I want to do is have a look at
this other battery compartment, right? And I'll describe it to you. And while I'm going up to get
a third battery, you can have a think about it. What the result will be. So I'm examining
the battery compartment. It's got three battery compartments, one, two and three.
So the first one has got a spring in it and it goes down to its negative point, it goes to a
plus point. The plus point seems to be mechanically the same piece material that goes to the minus
point of the middle cell, which is one, it says on this one, 1.5 volts. So it goes down, it goes
across, the springy bit comes up to the top. Now, if I look at the top, I see that battery compartment
one that we've just visited, that we've left from, is not connected to battery compartment two.
The top battery compartment two is connected to the top of battery compartment three. Battery
compartment three runs down to the bottom and that is not connected. Bottom of battery compartment
three has a wire that goes all the way back and out, but it is not connected to the bottom
of the other two batteries. So the battery, power from, if you put in three pixies here side by side,
each of them one and a half, one goes down, pushes behind the other one, which pushes behind the
other one. So while I'm going to get the third battery, can you try and figure out what the
voltage is going to be from this? And then back with another type of pixie from Panasonic.
This one has got a voltage of 1.61. Now, it's not going to practice ever to mix
batteries from different providers, different manufacturers, or indeed from different packs. This
is best to get the ones that are made from the med at the same time. And the reason for that is
they can be slightly different, make up in the chemistry so that if one of the pixies is a little
bit weaker, the other ones are pushing it at the whole time and kind of damaging it. So,
but for the purposes of this, I'm going to put it in, I want to get a measurement and we'll see how it
goes. So all we're doing is we're putting in plus coming out negative to a plus, bridging over
at the bottom to a minus, minus goes up to the top, it bridges over to the plus and the plus goes
back on my LEDs light hop. And if I put a measurement here measuring from the spring,
compartment one to the far end at the bottom of battery compartment three, I can see that instead
of three volts I have 4.6 volts. So that will be 4.5. Interesting, clap yourself on the back if you
got that. And that, because that tells us that all of these are in series, series, they're not in parallel,
they're in series. So I'm going to put that battery compartment away because it's
the job for another day and I'm going to put the other battery compartment away as it also is a job
for another day. Now that brings us back to our two very lights. So one of those battery packs
runs at five volts whereas the other one runs at three volts. So I need to be making sure that when
I take DC voltage in this, this thing needs DC voltage in order to run. And how much DC voltage
that's a very good question. Okay, change my mind, took out the same battery holder that we had before
and I have cut the wire off because it was attached to the string and now what I'm doing is I'm going
to check continuity on that. And I figured out what was going on with the battery holder.
It actually is not just straight connected, it's got a little piece of circuitry in there that reacts
to the light and if there's any light then it turns itself off. So when I measured it, it had
3.1 volts. So electricity is, we've learned several things. Alternating current is the pixies moving
over and back. Direct current is the pixies walking slowly towards Santa. Strength of the pixies are
the voltage but what we also want to know is the current. How many of them are flowing through
at any one time. So we can describe electricity. It's not enough to know the volts, to know what's
gone on. It's kind of similar to looking at a river and you need to know whether it's how big the
river is is the voltage but how fast the current is flowing is the second thing. So there are
three things that make up that are related to each other in describing electricity. One is
volt, voltage. The current is voltage, so voltage potential difference. That's how strong the
pixies are. Amps is how many of them are passing through at any given time. And then ohms or
resistance is the constraint on us. So if you think of it from the point of view of there are pixies
in a pipe and the pixies behind are trying to push the other pixies through a gap and the gap
itself is being tightened by an elf. That elf is the resistance and that's in ohms, the amp,
the amount that's going through is the amperage. But let's not concern ourselves with that. So if
you know one, they're all related using a thing called ohms law. So V is equal to i over r.
Voltage is equal to current multiplied by the resistance. So amount of volts that you have
available. If you know the resistance and the current, you can determine what the voltage is.
If you know the voltage and the resistance, you can determine the current. And if you know the
current and the voltage, you can determine the resistance. If you know the current and the
resistance, you can determine the voltage. So if you have two of the three, you can determine the
other one. And any two of them is enough to describe what's going on. But we, so in our situation
here, we needed to know the voltage. And what we need to know is, so the voltage that these
lights are going to light up with is three volts, the number three. So what I want to do is connect
it up to a USB power supply. Okay. So USB power supply, let me go to my box of USB power supplies,
which would be, which is actually in the box called USB cables. But that's a problem for an
only day. So let's go here. One of the things I've cleared out for all of the older power supplies.
Most phones now need two and a half amps. And we talked about amps earlier on. Amps is current.
B is equal to I over R. So the I is the amps for some strange reason. Well, there are reasons
that the named after famous people who did interesting stuff for an electrical engineer. So I'm
going to take this wall wart. So you plug that into your normal phone charger. And on the other
side is USB cable. Okay. I'll put this box in. I'll be back to you in a second. So,
healthily, this thing tells us information on the site. I think they're legally required to
or the wouldn't bother. So the impulse is 100-240V. So we learned about volts here earlier on.
So what do you think that means? Because beside that, it says it's that's quickly simple again.
That's like a wave. 50 slash 60 hertz. Interesting. We kind of know what volts are. And we know that
it's AC. So that's telling us that it is 50 or that it is 100 or 240 volts. So this thing won't
blow up if you plug it in in the US. And it won't blow up if you plug it in in Europe or the UK.
And the 50 and 60 hertz. Hertz is frequency. Frequency means the count how fast you can
fast it goes over and back. So those pixies, the the Grinch push in again against the L's
using the pixies left to right, left to right, left to right. That's the hertz. So 50 hertz
or 60 hertz. So in the US, I think they use 50 and over in Europe we use 60. So that's fine.
Now it also says max 0.2a. Hmm. A. Do we see that before? A is amps. Amps is current.
All right. Okay. Then carrying on output, it says 5 volts. And instead of the squiggly thing,
we have the two horizontal lines, the long one. And underneath that a dotted one saying 1.0 amps.
So this thing can take in normal mains power. And it will give you out 5 volts DC
up to 1.0 amps. Now the up to part you need to think about that is how many pixies you can fit on
the road. Right. So if you have a big huge motorway motorway, what's the American word for motorway?
Freeway, Interstate. You can fit lots and lots of pixies there. But if you're down at boring or a
small walkway we say to canal, you might only be able to fit one. So the amount of current
is determined how many pixies can you get passed at any one point in time. So there we go.
That's. And the current, the maximum we can pull from this is one amp, which is more than enough
to kill you. Okay. Goes across your heart. What happens is inside your heart you're basically an
electrical machine yourself. And the signals to that pumping machine in your chest is done using
electricity. And if you get that across your heart, it interrupts the electricity from your brains
and the signals down to turn off, turn off, turn off, turn off. So we don't mess with electricity.
Hungry pixies. We don't mess with. Yeah. So generally we say you're pretty okay with DC
currents, direct, direct current. But the reason for that is because it is low power, low amps,
low. So it's lower voltage, lower amps. You're in the millions. So a little thousandths of an amp.
And you should be safe enough. Okay. Once high to my desk, I better get a starter.
Guess I better take a photo of this. Let me see photo there. One side, I have a battery power unit.
So that is going to supply three volts. And the other one, I have something that's going to
supply five volts. So how do I get from three volts down to five volts? So if you were doing that
on an interest stage, what you would probably do is put in a toll bridge. And that reduces the amount
of traffic that's allowed to go past. So you tighten the roll down. You put in a bit of resistance.
And that's exactly what we're going to do here. And resistance, again, is part of the own slow thing.
Voltage on the top. The is equal to IR. So if you're not that good at maths, right? You think of
V. So put your hands in the air, right? V make a V symbol like V MCA. So two hands up, V is at the top
of a triangle, yeah. And then underneath that, you've got I and R. Just matter which side the
I and the R, it's important to know that V is at the top. So if V is at the top, then
and you want to know what the current is. Current is in is written as I and it's measured in amps.
It's the thing you have to learn, need to know. So what you do then is you divide voltage by the
resistance because V is at the top and there is at the bottom. If you know the resistance, V is at
the top and current is at the bottom, so you can divide the current I into V. So easy enough.
That's as that's as complicated as the maths as likely to get for you for a long while.
So what we're going to do is we're going to put in a resistor into in between the
in between the output of the phone charger and the string of lights. We're going to put in what's
called a resistor and what it is is a piece of wire that's one really tight and the electrons
the pixies in this have a real tough time going down. You get them in various different sizes. So
they're made with various different resistances they're called and they're named after a guy called
Ome and it is George Simon Ome who was a German physicist and mathematician. As a school teacher,
he began his research with a new electrical cell invented by the Italian scientist
as a Sandra Volta. See there? See there? Using the equipment of his own creation. Let's see.
And then we go to Ampere. One Ampere is equal to one Coulomb moving past a point at a second.
It is named after the French mathematician and physicist Andrea Marie Ampere. There you go.
And Coulomb just out of interest is the amount of current, let me go to the explanation,
and it of course is named after Charles de Coulomb. So all these units, the reason they don't
bear any resemblance to their letter is that the letter was already taken up by something else
and they're named in honor of the person. So the Coulomb is an electrical charge
and it equals the number of one Ampere constant current, one voltage. So it's actually the number
of electrons that pass a particular pass one amp of current in one second. So when I said
earlier on that the pixies are queuing for Santa, if you have a lot of pixies queuing up,
it's the number of pixies that go past in one second if you have a current of one amp.
And it is 6.241509 to 10 to the power of 18. So yeah, that's a big number.
They don't move very slow but there are an awful lot of them and they're very hungry.
Okay, so what are we going to do? We're going to put in a resistor.
And a resistor is a passive two terminal electrical component that implements electrical
resistance as a circuit element. In electronic circuits, resistors are used to reduce the
current flow at just signal levels to the wider voltage bias active elements. Blah blah blah blah blah.
Their symbol is a two lines coming out of a rectangular box.
Okay, where was I? Yeah, so I'm going to use one of them. You can get them for peanuts from China if
you can't have a look at any older electrical equipment and you'll be able to salvage them from
there. But we need to know the resistance. We need to know what value of a resistor we're going
to put in here to basically slow the pixies down from five that will be traveling a five
folds down so that they'll be traveling equivalent to three volts using the same amount of current.
And if it's not obvious at this point, I'm not an electrical engineer. I'm a mechanical engineer.
And this as this sort of stuff has been a struggle for me all my life I went from doing
mechanical engineering course first three years to doing our first two years and then the final
three years of my degree was in a different location and I streamed in where they assumed that you
had the knowledge of the first two years and I really missed that. So here I am teaching this more
to myself than to you guys. And if anybody else out there has got a better explanation or better
way to describe this please do a show because we need this for our amateur radio show.
So this has been going on a long time. I'm not going to edit it but I still haven't done what
I needed to do. So I'm going to continue on there. Right I need to figure out what resistor to use.
So if the two batteries were in series they would produce three volts and they do. So I now have one
part of my triangle which is three. I need to find out what the resistor is. So therefore I need
to know the values of V and I need to know the values of i. So the resistor I need. So as the electricity
goes around the circuit it goes from three volts on one side to zero volts on the other and that's
called dropping the voltage. So those all those LED lights use up three volts of electricity.
But I have five volts coming in so I need to put something in between that it uses of the
difference between the five volts and the three volts. So that's two volts. I need a resistor
that will use up two volts of electricity so that not too many pixies are hitting my LED lights.
Okay so the thing about DC electricity is it goes from one from the positive to the negative
goes around in the loop and it has to have a closed loop a little circuit that we call it
in order for it to work. If there's a break in the circuit the little pixies can move from one
side to the other the electrons can move from one side to the other so therefore we don't have
complete circuit. So one direction we call positive the other direction we call negative
it's arbitrary don't overly worry about it. The positive the negative is actually the directions
that the pixies go because they're all grumpy but if you're looking at circuit diagrams you'll see
the arrow going the other way from positive to negative it doesn't actually much matter as long
as you know about this. So I'm going to I've got my unit here and I'm going to quickly the battery
compartment is here with the batteries inside it and the thing I noticed is that it doesn't work
unless the light is off so I've got some black electrical tape here and I'm going to
very quickly put back the screws in the compartment and you have no idea how much time I lost
on this project as a result of that little misstep and put the screws back into the battery
compartment so I have the battery compartment because I want to be able to measure the current
in this so in order to pick the resistor I need to know how much current these LEDs take up
most power supplies are the batteries are the one you just will try to push as much current as
they can whereas the other devices are not able to handle this so you need to be able to control
the amount of current gone through at any one time and I have the electrical tape here and I'll
just cover a few strips at the front
so I now need to check and see if the direction is correct and I do that by just connecting
quickly another great way of doing this is getting a small single cell little battery
the CR 320s 3220s those ones and put them all where the other they have so little current
so they have so little power strength that they are not going to damage your circuit so in this
case I know which one is positive and I know which one is negative so that is great because I
measured it on the battery on the multimeter or positive volts and if you put it on the multimeter
I'll just do that again I'll switch it to the voltage section I'll switch it to voltage DC
I've got my unit supply power I get my black need and I get my
red lead and I pick arbitrary sides so one side is connected to black the other side is connected
to red so I'm seeing minus three point two volts what that tells me is that the red is connected
to the wrong side and it's reporting that the pixies are going the wrong way the electrons are going
the wrong way so I know that this side here is the negative and this side here is the positive
so what I'm going to do is switch them around and just measure them again and now it's positive
so on the one that I held to the back lead I'm going to take a tiny little bit of
of black insulating tape and just put it on there for a marker so that I know that I'm connecting
the wires correctly so I'm going to connect on to the LEDs and just twist in the LED wires around each
other and they should light up but they're not lighting up why is that
so they're working on lighting up now I'm connecting them the other way around quickly
tapping them to see if they're light and yes they do yes they do but at the end it's very
flaky because of the there's still insulation on both sides so not a great connection I'm going to
go and get some sandpaper from the shed and I'll be back in a bit okay got some sandpaper
script those off the connections are a lot better because the installation's gone off them so now I have
them lighting up with the original battery pack there's a more work than I thought it should be
the majority of this is I'm stringing this out I have no idea why I want to tell so much stuff
and I don't feel I'm an expert but anyway we will continue on so now I've got this
connected up using the original battery supply I'm going to split the circuit there and I'm going
to put my multi-measure into the circuit so it can tell me how many electrons pixies are walking
past on the circuit so what I'm going to do is I'm going to switch it from volts the red lead
from volts to milliamps I'm going to switch it to 20m let's see if that's a good start and in this
case the black and the red of the multi-measure don't really matter because what's happening is the
current will come out of the electricity will come out of the battery going down one lead into the
multi-meter and out the other and as it goes past it passes what's called a current shut and
the multi-meter will be able to determine how much voltage is going past there and then by using
normal internally it's able to tell us how much current so I'm going to hold it there and I'm going
to hold that here and now the light's light up and I'm showing zero on my one on my multi-meter which
means this is not an auto loving multi-meter so it means that the amount of current going through
is more than it can display on the unit so I switch it up to 200m 200 milliamps so that's 1000 amps so
the display is now showing 98 up to and it varies up to 102 milliamps so what we can say
is that 100 milliamps is flowing through that cable 100 milliamps is flowing through the cable
what's I'll just make note of that so does that seem right is that correct so what I've done is
have gone and counted each of the LEDs in turn and they all together will be using some of this
current so if we divide the number of LEDs by their total number we get the amount that each one
individually is using so they're using 0.005 of an amp each which means they're using 500 micro amps
or 0.5 of a milliamp so quite often electronics milliamps are used so they're using half a milliamp
that seems very little to me but gone over to the EEV plug forum and they say that these type of LEDs
use between 0.1 and 1 milliamps so 0.5 is smack bang right in the middle there okay great however
what we need is the total current so that's the one we're interested in and that is already as I
said 0.022 amps so we need to know what sort of resistor we're going to get in order to drop those
two volts so we use ohms mode to determine what the resistor is V is on the top V is for
victory you've clamped to the top of the mountain V is for victory but in two and then we divide that
by 0.022 amps and the answer is we get a 90 ohm resistor 90 ohm resistor two volts divided by
it gives us a 90 ohm resistor very good so I look at my park store and I know there's going to be no
90 ohm resistors but what they're hard going to be is 100 ohm resistors which is close enough
when you're doing resistors the bigger is probably better so what I'm going to do now is I'm going to
put this resistor in line with the positive end of the connector coming out of the USB I'm going
to wire it through my voltmeter as well and I'm going to confirm all these calculations work in real
life so I've just done that I put in the USB connector PCB it's basically a USB connector and
it's got a small printed circuit board that comes out with place for four holes two of which I'm
interested in which are the voltage positive and the negative positive and the negative is usually
called ground so those come out of the battery pack and I've got the 100 ohm resistor tied around
the negative are the positive lead that goes out to crocodile flip through my voltmeter and then
back to the lights now the lights light up and they're showing that I've got 2.6 volts coming out
and I've got 200 milliamps so a little less voltage and a little less current so what all
and all the current should be around about the same so that's the same regardless of what I did
but the amount of voltage being dropped has meant that there's two volts being dropped on that
little resistor so that is pretty much that now what I need to do is take my voltmeter out of the
way and tidy this up, solder it and have it ready to rock by tomorrow so let me do that now
first thing first I'll disconnect the USB connector and now this is where I need to
make sure that I don't mix up the ground and the positive and negative
okay let's get our soldering gear out which we have here I don't actually have keychrank
that's big enough to go around a USB connector so what I think I'll do is I'll get an old USB lead
that's I'm not using and just cut it and you just strip the wires and join the wires but
instead of using this PCB thing this PCB thing is handy for testing so I'll take a photo of that
because I can attach crocodile clips to it but for this purpose purpose of this I just want it
on a USB lead and my heat shrink will heat shrink by the way is like a plastic tube that's
double the size so you put it over the wires and then when you want to seal your electrical
connection you heat it up and then it shrinks down to a half its size and it's like forms
insulation on the outside of wires that you have stripped and you've stripped them because
you needed to strip them because of the you needed to make electrical contact with them
so that's what that is so I've got a sacrificial USB cable which I'm going to cost
and cut that at the end so I've taken the head off so I've got the male connector
the type A connector on one side or let's call that the bit that usually fits into a PC
so some USB cables they have two wires so they're power cables and some have only one
some have four for data this one is a keep cable and it's data only it's only for charging so
that actually suits me absolutely fine in this case because that's what I want so I'm going to cut
one of these short as I said I'm going to cut one of them long now the first thing I need to do
is to where's the end of my straight lights is just falling in the floor
something that it's been doing the whole time so put a weight on that
now the thing you always forget to do is put on heat shrink so um that's something we're not
going to do here we're not going to forget this time I guess we're rocking that positive
with red sharpie and the negative with black so I don't forget this now it is difficult to know
on a you know these cheap cables from places you can't be really sure if they're wired up you know
the black is positive and white is negative which is the convention or possibly red is positive
this one has a pink cable and a white cable so rather than take the word for them guessing
that white is negative and that pink is positive but you do not know so I'm going to
pop it into the tester really quick and check my hypothesis so I'm putting the pink
onto the red and the white onto the black and yet 2.7 volts so the white is black is negative
so I'm just like that I don't want to actually have a red cherry I just have a black hammer pen
which will do which will do which will do so now what do we forget and care we're forgetting
what you always do forget to put on the heat shrink so I'm going to put on a nice big piece
of outer sleeving to cover both and that will cover go down over both are about four
orders of this into the show notes and it's yep just take this time and then on the other cable
I'll put a smaller one here let's see if that size yeah that size seems about right and I'll take
out two reasonably generous pieces of that
so I'll put a smaller one on the fairy light side and I have the larger one to cover up these two
on the other side and I've got my resistor in the middle and let me make a quick photo of this
whether I'll use that one or not now I will turn on my soldering iron
for which I will need a plug
so
soldering iron is on do I have a plan yes I'm going to take the two black leads I have heat shrink
on I'm going to twist them together like that and then I'm going to
do basically put a blob of solder on that so my iron is heated up I'll look on HBR for mistracks
to show on soldering still have warm enough to melt a solder but it is now so I'll bring it to
the tip to the solder or to the wires hold on to the wires bring in some solder and remove it to
tie this little bit older for a second and then move it away that's it done that's that one
done and then the question is the positive so I'm putting the resistor on the positive side I don't
think it's right you watch matters which side you put it on as long as you do you want to
twist on one leg of the resistor it also with a resistor doesn't actually matter which way
you point it some components LEDs for example have to be pointed the correct way so let's
called polarity so I've twisted on one leg of the resistor I'm going to bring over my solder
iron again put on solder and then off bring it over to the twisted wires put it on the
resistor wires and then he's up the twisted wires a bit and then bring my solder in from the other
side touches it melts basically it's just metal-looming and then all my solder up a little bit of
small comes off that's the resin which is there to protect they to stop the joint from getting
oxidized as a melt they oxygen from the air comes in on a texite but the resin keeps they
oxygen away so it doesn't get damaged okay so that's one side soldered the other side is
hugely far farther away so I'll modify the cable a little bit stretch it down so that they're
more or less together this is a fierce exciting stuff
and now I'm going to cut the wire pink wire lots shorter I'm just going to strip it with my
stripping to twist the cables on that make sure the resistor is more or less in place and then I
just go to oopsie a bit tricky where I'm just going to screw the cable together so it's
other foot resistor is wound to the cable I'll just run that back again the solder when it's done
will make a good mechanical joint as well so I'm not that particularly worried about it but
I just want to out of the way the legs and legs resistors are quite long okay so that's it there's
actually a total three solder joints to be made on this two of them are one on one side and two
on the other side of the resistor so it gives you an idea of much soldering there is to be done
so I will again repeat rinse and repeat the same procedure that we had before
soldering iron's hot where did I put my solder yeah I bring the solder over to the twisted wires
leave it there for a second to eat up the wires then from the other side bring in the solder
itself and then it melts goes up yeah you can see it it wicks as I say it's absorbed it wicks into
the wires and then you know you have a good joint and leave that for a second to cool people say
don't blow it but there you go so let me tidy up my mess here a little bit and I can turn off
the soldering iron you will get burnt with a soldering iron it's just a matter of fact it's not
a question of when it will happen but you know you'll survive don't worry about it so let's have a
look here as they okay I've just made a photo of the setup and in that photo you can see
the volt measure that I used and it's currently set into the volts DC position then the battery pack
with the USB connector the power supply that I intend to use some example LED light sets with a
two battery components and three battery components the one with the installation tape is the one
that we've been using during this epic and of course what are the little cable that I've plugged
in just before I do the heat shrinking on it so that's where we are at this point and the next
thing to do is plug it in and see if it works and yes it does add a moment of terror there because
my battery pack it's taking so little current that the battery pack turns off so I'm now going to
try it on a wall wart and see what how we get on
right put it in and it gets lights up and does it stay lighting over yes it does
used in we have success okay the only other thing to do now is to do the heat shrink
unfortunately I happened to have a heat shrink into for that very purpose
now it's essentially a hot air gun so what I'll do is you can use a hot air gun or you can use for
example cigarette lighter so I'll go the cigarette lighter hook here for now and
as that's simply going to give me more control of where I put the heat
you got underneath it holders a bit away so the flame doesn't touch the heat shrink and the heat
shrink shrinks but oh and as it does that's that now I'm going to get the heat gun because I much
prefers over the
it's basically paint a stripper heat gun that's what that is so it's hugely working for this
job but there you go I just really hot now cool it off and then I pull down the other heat shrink
and I'll heat shrink all of that of course
of course the LEDs go flying across the floor
so that's it point of no return plug it in and it works
puke for a quick second it didn't work so that's it everybody tune in tomorrow for another
exciting episode of Hacker Public Radio
you have been listening to Hacker Public Radio at Hacker Public Radio does work today show
was contributed by a HBR listener like yourself if you ever thought of recording
podcast and click on our contribute link to find out how easy it means hosting for HBR has been
kindly provided by and onsthos.com the internet archive and our syncs.net on the
Sadois status today's show is released on our creative commons attribution 4.0 international license
