Episode: 1828
Title: HPR1828: Multimeter Mod's Part 1
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr1828/hpr1828.mp3
Transcribed: 2025-10-18 09:49:33

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This is HPR Episode 1828 entitled Multimeter Mods Part 1.
It is hosted by Enable and is about 19 minutes long.
The summary is Enable modifies its multimeter to add features to feel lacking.
This episode of HPR is brought to you by An Honesthost.com.
Get 15% discount on all shared hosting with the offer code HPR15 that's HPR15.
Create a web hosting that's honest and fair at An Honesthost.com.
Hello, this is Enwai Bill and today I thought I talked everyone about a little hack I have
planned for here for a meter that I use.
A while back I heard about these Unity meters.
This one is a UT61E, so UNI-T-Aula linked that in the show notes.
For a hobby multimeter, this is not bad and they're not expensive, let me look it up quickly.
So I just looked it up on Amazon.
This particular model is $49 currently.
Now what this is, it's basically a Chinese knockoff of a very expensive like a fluke
or an adulant where you would be up in the $500 range.
I'm not kidding.
A handheld multimeter push in $500, $600.
Here they've come out with them for $50.
I don't think I would use this one professionally.
Professionally I use a fluke because I know I'm going to be putting my probes on some very
high voltage and if something goes wrong, I don't want the thing blowing up in my hand
and fluke and some of the bigger names, the adulants, they have blast shielding actually
inside the meter.
So if something does go wrong, you blow those fuses that are in there.
There are interconnected pieces of plastic blast shields within on the inside of the unit.
It's hard to explain but it's so that if it, if something does go wrong and something
blows out, it doesn't blow out the side of the unit and you're holding it in your hand
there and well, you can imagine.
These are built kind of cheaply, these unities, however for hobby use, I don't see how you
can go wrong.
If you're a hobbyist, if you're messing around with, well, like I'm going to get into talking
about in a minute, you know, just your components and your capacitors and your resistors and
your arduinos and your arpise, this is a great, this is a great meter for $50.
It's got every function you're going to need, like voltage, millivoltage, ohms, capacitance,
hertz, micro amps, and you know, everything's there.
It also comes with this little capacitor diode checking duhiki, I haven't used that yet.
It also will data log so you can leave this thing running on something for an hour or two
hours a day and come back and download the data to a computer.
Now I think, well, I know it said it was for Windows only, I'm sure I could get it going
in wine, but I haven't even bothered with any of that.
The downfalls to this, personally, well, two little things I didn't care for is it doesn't
have a backlight, my fluke, I just turned the backlight, as soon as I turn the thing on,
I turn the backlight, it's sometimes even if I'm out in the sun, it's just like a habit
for me to hit that button so I always have the backlight going on the fluke, the light
will time out after a little while and you might have to press the button again.
The thing I really missed on this unity over using my fluke is the timeout.
I'm so used to just setting my fluke to voltage, I go, I take my reading and I throw the
thing back in my tool bag and I don't know how long the fluke timeout is, but it times
out and shuts itself off and you save your battery.
My fluke battery will last, geez, if I change it once every three years maybe and I use
it almost daily, that's a very handy feature.
The first three or four times I use this unity, because I'm used to my fluke, I set it
at the voltage, I do whatever I'm doing, I set it aside, I come back the next day and
the battery is dead, because when you leave the function dial in a function, it just runs
and runs and runs until the battery dies.
So I think this is a good opportunity for a little hacking here.
What I thought I would do is open this thing up, have a look at the guts inside, see
how much room is in there.
And I think I could just add a couple LEDs to the LCD screen and light that up and then
using a MOSFET and a momentary switch, I can have this, I put a little, I'll put a
little switch on the side, I haven't yet, but just a momentary switch kind of like you
might see on like, I guess iPods had them or audio players, something you just pull down
for a second and then let it snap back up.
Now what that's going to do is I can interrupt either the ground or the positive, I suppose
it doesn't matter on the nine volt battery.
So I'll have the positive for the nine volt battery go up to a momentary switch and then
that's going to charge up a capacitor.
The capacitor is going to drain through a resistor.
So the capacitor is going to hold voltage for quite a while, depending on the capacitor
you use and the resistor you use, then the MOSFET picture it like a switch.
So I want to switch nine volts to this meter and then I have a power drain situation with
the capacitor and the resistor.
So what the MOSFET will do is close a switch as long as it's within a voltage range.
So the one I'm using I think was a voltage range from 20 volts to I think right under
three volts.
Anyways, I'm going to be using between nine volts because there's a nine volt battery
in there and we'll see where it runs out.
I can do some timing.
So I'll pick the right resistor and capacitor to have a proper drain.
So what that MOSFET is going to do is hit your momentary switch, it charges up the capacitor,
the capacitor pulls in the MOSFET, so to speak.
And that lets the nine volt current go through two pins of the MOSFET.
So then the MOSFET's going to be still watching that capacitor as it drains and it's going
to hold those two pins in and send nine volts to the meter and to the LCD, LCD, the LED
lights on the LCD, until the voltage drops below, well, we'll say two and a half volts.
So I'll link to some pictures in the show notes, I got the unity open, the meter open,
it looks like there's plenty of room in there to put switches and the capacitor and the
resistor.
I open it up further.
You can look at the show notes if you want the pictures if you want where I'm flipping
it over and checking out how the LCD screen works.
LCD screens have like a like a white plastic behind them.
And well, this is how your monitor and your notebook works too.
There's like a white plastic, sometimes it's like a honeycomb type of feature and then
a bulb will shine up through the plastic and depending on the honeycomb structure or
the density of the plastic, you'll get an even light.
When I looked at it, I saw it had that white piece of plastic back there and it had two
little indents.
Like you could, like maybe there's an upgraded version of this unity that does have a backlight.
But it looks like there was already two little notches in that white plastic for LED bulbs.
So I had to find some LEDs in my bag.
I had red ones, yellow ones and green ones and I tried them and it none of them looked
very cool.
I mean, it's a red meter and you put a green LED in there.
It's going to look like Christmas and the yellow ones are going to make it look like
Easter or something.
So I thought what might be cool on this one is a blue LED.
I was going to wait and order some blue LEDs for this and then I recalled right after
Christmas, I was in a store and they were selling all the Christmas stuff at like a huge
discount, all the decorations and that.
And on the bottom shelf was LED Christmas tree lights and they were like $2 where, you
know, the day before Christmas, they were $20.
So I thought, ooh, I'll just buy these for two bucks and I'll have 50 LEDs I can use
in future projects.
So I recalled that.
I went down into the basement, into that Christmas tree box there and see what colors
were in there and they had red, green, yellow and blue.
So there's my blue LEDs.
So I got those and if you look at the show notes, you can see me kind of building up a
little LED wiring harness.
I had to get the spacing on the LEDs right to fit into those two little notches on the
white reflection behind the LCD screen.
And I also put shrink wrap over everything because right near where these wires are going
to run, there are contacts on the board where the function buttons in the front go down
and press.
I didn't want any traces or solder from the LED harness to be touching any of these
pads mistakenly.
So I installed this harness under the LCD in that those two white plastic notches and
then the wires and the leads kind of curled around through the the relativity and peak
button and then around the blue option button on the unity and then the other side of the
leads came down between the hold and the range buttons and then up around the yellow function
button.
So I don't know if that really helps describe anything.
But if you look at a picture of this meter, you can maybe you can kind of tell how I
routed the wire and then there was a cutout right there between underneath range and relative
that is there was a hole in the PCB for one of the screws that holds the whole case together
to come up and go into a screw mount.
So my red and my black wire from my LCD harness, this is getting confusing, LED harness went
through that hole in the PCB so it went into the back of the case where I can mount a switch
in the capacitor and all that.
The next thing to work on would be the MOSFET circuitry.
So I got my breadboard out and I found a momentary switch.
You can see pictures of that as well and I just wired it up.
I actually put the unity back together while I was doing that because I wanted to use
it to watch the voltage drain on the capacitor and I had a decade resistance box.
So I can just dial in resistance and try and get something close to 10 minutes.
I had a 470 micro farad electrolytic cap, what voltage is that?
So a 16 volt one, I just had it lying around.
And then I dialed in the resistance so the drain of the cap to get to the amount of time
I wanted, which was around 10 minutes.
Turns out with a one mega ohm resistance on this 470 cap, I was getting 10 minutes and
40 seconds.
So that's close enough for me.
I just, I want to pull the meter out, turn it on, do whatever I'm doing, which may
take 30 seconds or it may take 3 or 4 or 5 seconds or I just thought 10 minutes was a good
window to turn the meter on, use it for whatever you're doing.
You might tweak something over here and then you grab the probes again and you test something
again.
And I figured if you're not done in doing what you need to do in 10 minutes, it's not
such a big deal just to turn the thing back on again.
Of course this is going to mess with the recording feature.
Hmm, I just thought about that right now.
I don't ever plan on doing that recording feature where I'll watch some voltage over
an hour or a day and then go back and look at it.
I don't plan on doing that.
I suppose if I ever found I wanted to, I could just change the switch from off momentary
and then like, or maybe it would be on as up and then off as in the middle and then down
as momentary.
Maybe I'll look for one of those.
Then I'll have the option to just pull the little switch down to momentary and it
pulls in the MOSFET, it sends power to the meter and the LEDs, it runs for 10 minutes,
it shuts off.
Have the thing running for a day, I'll push it up into the on position.
Now I think I might actually go and find, see if there's a on off momentary, small little
thing that I can mount.
There's plenty of room behind the LCD in like the back of the case that the, you know,
the case splits in half, that whole back area back there, there's like nothing back
there.
I think they just continue the form factor up just to, you know, make it look impressive,
I don't know.
Okay, I'm going to pause here because I just finished, I got the LEDs in underneath
the LCD and I have the MOSFET circuit running at 10 minutes, 40 seconds on my breadboard.
So I'm just going to have to find a switch I want to use and then solder up this resistor,
this capacitor and this MOSFET in like a little tiny package and I'll probably just shrink
wrap the whole thing and just have a couple of leads coming out.
And then I'll put it in the meter.
So you won't know I'm pausing, you won't notice any time lapse right here, but at least
the day is going to go by while I go to somewhere to look for this switch.
So I guess this is intermission, I should place some music.
Okay, I'm back, that little blip in the audio there was about 24 hours gone by.
I continued to play around with this circuit a little more and I also went online looking
for that switch that I wanted to find.
I couldn't find an on off momentary switch, well I did find them but they were large switches
they seemed to be for automotive applications.
What I want is a little tiny sub micro, just I'm sure you can imagine what I'm looking
for, just a little tiny slider switch.
I wasn't finding one in on off momentary but then like at the last minute on Mauser,
I found a little sub micro slider switch that was on on momentary.
So this will work fine for me also.
I'll have it set up so if I click to switch up, the meter is on and it will stay on.
If I move that switch to the middle position, I just won't use those terminals for that
second on feature.
So that'll be just like an off.
And then pulling down will be momentary, charge up the capacitor, have the MOSFET do its
thing and when you release it's momentary, it goes back into that middle position which
is effectively going to be off.
So that was one order, I got that from Mauser and that's going to take, you know, five
to, you know, could be two weeks.
Then I'm up after ordering that and I'm playing around with the breadboard and I took the
LED out that I was using for testing and timing with the MOSFET and I had it with some alligator
clips up to the meter to just check that it would run the meter and it did not.
So what was happening there is the meter is trying to draw current through this MOSFET,
those two legs of the MOSFET and it's taking the voltage down from nine volts and bringing
it down into like the low eighths which is not enough to power up this meter.
It's going to need more current than that.
So I'm going to need another component.
On Amazon, I found a 10 pack of little really tiny relays, nine volt relays.
So I ordered that 10 pack and, you know, if it's prime, it's free shipping, it'll be
here in a couple of days.
I don't know, it was like three or four bucks.
So then I'm thinking, well, this is going to be two weeks, I don't want to wait two weeks
with this meter half open and these wires hanging out.
So I thought maybe I'll make this into two mods on this meter and I can make it also
two episodes for HPR.
In a couple weeks, I'll record a second one and it will be about the mod for putting
the timing circuit in this.
So now I took out a meter, I started poking around in this unity while it's running to see
if there's anywhere I could pick up nine volts.
And up near the dial, there's a series of four small capacitors.
And at the first capacitor, there was nine volts there.
Now I don't have a schematic for this.
I mean, I don't know if there's one around, but if I had to guess, I bet those four capacitors
are where the nine volts comes in from the battery.
And whenever the dial goes into any position, it sends the nine volts into these four capacitors
for power conditioning.
And then after the capacitor, there's a nice smooth current.
It gets sent down to 3.3 and you got a nice steady current to run the whole system.
So what I did was on my LED harness, I cut the black wire and I have that over, soldered
to the negative of the battery terminal.
And then I took a 3.3.3 resistor on the red wire, soldered that on, put some heat shrink.
So nothing's going to touch.
Cut the lead of the other end of the resistor quite close and stuck it on right at that first
capacitor where I was getting nine volts and soldered that up.
That allows this meter.
Any time the meter is on now, I got my blue back, black.
Any time this meter is on now, it has the blue back light.
So I like that.
So the only thing I might do is put some hot glue on this because the way that that resistor
is connected to the terminal, it's not going through a through hole and it has nothing
retaining this wire.
So this is going to be like handheld thrown down on tables, jumbling around in bags and
things.
That might not be a very good connection for the long haul.
So I'm going to hot glue, put some hot glue around near that connection just so it retains
the wire and doesn't have any stress on that connection.
Okay, so I'll call that, I'll call this episode one and I will record episode two when those
other parts get here.
So if anybody wants to leave comments in the comment section or if anybody wants to email
with questions or comments or whatever, I am NY bill at gunmonkinet.net and I'm still
on status net, starting to work towards going, getting a GNU social instance because I feel
like there's no more updates coming for status net.
I'm working on that but for now, I'm still on status net, it's sn dot gunmonkinet dot
net.
Okay, until those parts come in now, talk to you guys later.
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