Episode: 3809
Title: HPR3809: The Abominable Post Apocalyptic Podcast Player
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr3809/hpr3809.mp3
Transcribed: 2025-10-25 05:46:28

---

This is Hacker Public Radio Episode 3809 for Thursday the 9th of March 2023.
Today's show is entitled, The Abominable Post-apocalyptic Podcast Player.
It is part of the series Arduino and related devices.
It is hosted by mechatraniac and is about 20 minutes long.
It carries an explicit flag.
The summary is build a $3 MP3 player in one hour.
Greetings.
This is mechatraniac.
So I broke all my slave slabs that I used for podcast listening and I get all or most
of my energy from solar.
So I can't be just listening to podcasts on a laptop and plus it's not very portable.
So I wanted a podcast player that's portable and so I ended up creating an abomination.
I wasn't happy with the look of it for quite some time and I'm still not, but I use it
all the time every day, most of the day, most of the night.
So there's something to say for this design, I guess.
It's also a feature, you know, because it looks like garbage, so it'll be a useful feature
for post-apocalyptic robots when the townies get tired of the robots stealing all their
solar panels and plugging into their outlets and stealing their power and stuff.
The robots might get persecuted and have to disguise themselves as trash.
So speaking of trash, there's only two components that you should need to buy, maybe three.
And I'll put the links up to AliExpress.
There's the 18650 charger, which you can use to charge an 18650 cell.
So you might need to buy a cell, but I got all mine for free.
I've got about 100 of them stockpiled.
And you can find them in things like laptop batteries, power tool batteries that are lithium
ion.
Be extremely careful taking them apart where gloves use pliers.
The most dangerous thing about batteries I found is the risk of getting cut on those internal
conductors in the batteries between the cells because they just use these pieces of metal
and when you take them, cut them off, they're extremely sharp.
So that's that.
And MP3 decoder, this MP3 decoder is based on the GPD2846A chip, and we're going to look
at the database for that and look at some very ripe hacking opportunities, like unexplored
hacking opportunities in this thing.
But for now, we're just going to wire it up for the functions that are on it.
So on this MP3 decoder board, you see the SD card to the left of it, there's an SD card
in it, it's colored red and gray, it's just barely sticking out.
And it has three sets of pads that go to ground and once a set of functions for each pad.
So you're meant to put a switch across these two pads.
You can't see them in the diagram, I mean, you can't see them in the picture here because
they're obscured by my soldering job, I've actually got six wires connected there for the
three momentary switches that are on top of it.
But if you look at the AliExpress link, you can see a clean version of this and look
at the pads.
So these pads are active low, meaning the switch shorts them to ground, which means you
can control them from Arduino, which I did with my other robot project, the Herald Robot
project, go to itchute.com forward slash channel forward slash mechatroniac to see that
in action.
If you've listened to my previous podcast where I've encouraged you to get Arduino's and
you haven't, you're not too bright because it costs about twice as much now, but there's
still very much worth it.
So I put a link to AliExpress page with a sensor kit that comes with Arduino and a bunch
of sensors and think it costs about 50 bucks.
Could have had it for about 30 or something a year or so ago, but it's very much worth
it still anyway.
And that has things like the ultrasonic sensor and the infrared sensor, which would enable
you to do as I did and make the MP3 player attached to your robot be controllable by a TV
remote.
But I wanted to leave that alone and so I had this other unit in my box.
So the one that I've gotten my robot actually has four functions and it's a little bit
fancier, a little bit more expensive.
This one's like a $1 cheaper, it's like a couple of bucks just extremely inexpensive,
very good deal of best price.
But the other one had four buttons on it.
It had a jack for headphones and also USB input.
So this one just has the SD card.
Although this chip has the USB capabilities as well, but we'll get into that a bit later.
So the wiring is pretty straightforward.
There's three momentary switches.
All of this stuff other than the two boards, like I got post alpocalyptic style.
And if you're like me, you've got stuff like this post apocalyptic.
These chargers, they come in strips of five, so you break them off one at a time as you
need them and they have a micro USB input.
So you just plug in micro USB when you want to charge it up.
Just treat this as a black box for all purposes.
There's only two sets of leads going out because the input is the USB, that's the power.
And then B plus and B minus guess where those go straight to your 18650 cell or any other
nominal 3.7 volt lithium ion cell, you can use those gel packs as well.
And the output so and the output goes to the positive goes to the positive and the negative
goes to the ground on the MP3 player.
You can't see it because it's a little bit obscured by the wires.
You can sort of see it.
And speakers SP minus SP plus that's a self explanatory as well.
So for these momentary switches, I bought these LED lights.
They're on sale for like a string of 50 lights for three bucks or something.
I bought a bunch of those and each of them had this momentary switch with a little cell
battery in it so you could test the lights in the store and that's that's it.
That's the end of the use for it because you're supposed to put batteries in but I modified
these USB power packs.
But anyway, those momentary switches, I took the little cells out and connected them up
and I'm using them as momentary switches.
So those are supposed to be thrown away, but I'm using them.
Okay.
So yeah, I can't believe that's that's all the that's all the wiring pretty straightforward.
So the build itself happened to find this jar.
There's a high resolution for you can see what kind of jar it is.
3.5 gram size.
And it just happens to be the perfect dimensions as a speaker box for this like two inch speaker
that I found.
So the reason it's so awkward looking and kind of like a modern art looking is the speaker
magnet is pretty big and the 18650 cell is so long and ungainly I had to put it under
this big black lid some jar jam lid or something like that.
But the 18650 cell just fits right in there and I've got the wires from B plus and B minus
soldered directly to the 18650 cell is the note about safety and soldering can had concern
my last video about taking apart the batteries and and making I think it was the one about
my battery pack and soldering onto cells for that.
I found that the like I said again, the most danger is going to be in taking them apart
number one, secondary danger is burning your house deaf and if you puncture one but they
smell really terrible so you'd probably be able to throw it out if you have a pair of pliers
and take it outside.
They will alert you but they have the 18650 cells have a safety mechanism where before
to blow it's it's got a mechanism where it'll release the pressure so they've they've got
that safety built in but I've never activated it and I don't know you'd probably have to
try pretty hard to to make it explode from heat just that's just from my experience obviously
if you are soldering you want to use you know take as little time as possible maybe if it's hard
to solder I'm like some surfaces seem solder phobic almost I know for a fact some are really
hard to solder to so if it is try sandpaper or something there's tutorials on YouTube people
using spot welders made out of batteries so that would be it one way to go but I find solder is
quite adequate if you if you're really phobic about soldering onto a cell you can use one of
those elastic bands from a broccoli I don't know in Canada we have these these broccoli holder elastic
bands but you can you can strip the wires and just put the band over the cell and just tuck those
wires in appropriately per polarity and just go with that I'm actually doing that with one of my
solar powered chargers because I can't find my my little cell holder you can also order the cell
holders as well if you're ordering an 18650 you want it to be neat you can get a cell holder that
you could just clip in as well but anyway the cell is just hidden right under the big black lid
and yeah like I said these these these wires go down from the from the switch pads where they
don't have to they could have just gone up but I was going to have the switches be at the bottom
and have them just kind of have the the player just kind of stand on the switches but they're kind
of hard to align properly because the bottom of the thing isn't perfect so I just end up putting
them on top and I was too lazy to do the resoddering again so I just got them got the wires coming
back up from the top hopefully you can make yours look more elegant or not the anti aesthetics is a
feature after all robots might have to hide so I think that's it yeah so yeah you probably make it
smaller if you use a different type of cell and smaller switches and you know put the cell inside
the container bonus points if you put your stash in there too and have it removable but this works
the the first time I used one of these for the robot I bought of amplifier module as well because
I thought oh it's gonna have a really weak output right maybe for headphones at the most but I was
surprised these things actually crank pretty good for their size got a little off amp on there
and must be pretty efficient because they never get hot or even warm so
so you get pretty loud did I just like you out and you think the show was any
so it was pretty hard to track down the data sheets but I've got some there's one in Chinese that
has diagrams of applications and there's one in English which doesn't have the diagrams but
it's in English so there's quite a lot of features that you can unlock with different resistances so
I just started looking at this I just brought this up for the podcast but if I had looked at
before I sealed it up which I used oh by the way I used tape to hold it together just put tape
I guess I forgot to mention how I put it together it's it's just like gorilla tape and some
electrical tape taping down the speaker to the container and then more tape holding the lid
and then hot glue holding the USB charger and the MP3 decoder board and the lid has
cutouts on it but you can see one diagram you can see a little a little slit cut out for the
for the SD card and the other side you can you can see it it's got a nice LED when it's charging
it puts out a nice glow when it's charging at night all right so looking at the data sheet it shows
it shows up to eight buttons here with various different resistances so the one board had
that had only three and the other the other one had four but it's got up to eight maybe even more
it's also got line in this device is it puts out a mixed mono but if you you can solder lines off
with with some magnet wire I guess solder right and left off and put that to an amplifier if you
want stereo out of it so the chip itself the decoder chip does stereo it puts out FM clock whatever
that means it's got some applications where it shows an FM chip so it supports three different
type of FM chips so you can control the what band and what frequency the well yeah it's
going to be FM band control what frequency the FM is going to be on so yeah all of the functions
are from one pin can eight IOA for its labeled and it says A to D key buttons but we know it's
much more so she definitions previous next play pause volume up volume plus oh yeah the functions
on on this one are play and pause one button with a short press it plays the previous MP3 with a
longer press it turns down the volume and the other button with a short press it plays the second
or the next MP3 with the long press it turns up the volume and that should that probably conforms
it shows a different configurations depending on like there's a I guess it's a pull up resistor
that you put from the BC 3.3 volts through a 22k resistor onto onto the line off of this pin 8
and then all the resistors come off of that to the separate switches you'd be best off looking
at the data sheet for that the Chinese data sheet and it shows the little diagrams of the switches
this got an alternate mode as well and it shows how to hook up the FM receiver chips as well it
says it supports three different type of FM receivers so so nobody on YouTube has stepped up
to to unlock any of these features on these boards like there's a bunch of videos people
hucking up the boards but nobody's unlocked all these features here I'll read the features now
volume scan scan all FM so I got through the basic ones there scan plus scan minus channel plus
channel minus skip to the next frequency of saved FM rated you can save radio stations wow
I don't know how you do that mode mode switching in sequence SD card T card you disk FM line in wow
you kind of do a lot with this thing yay line in very interesting so I see we'll cut down automatically
if the mode is selected but the expected peripheral is absent repeat reading the keys again repeat
in two cycle modes which all and single cycle and EQ which I managed to get this I managed to
activate the EQ feature in the one on my robot with the resistor I forget what resistance yeah so
you could be you could be one of the you could be one of the pioneer hackers of this chip
if you unlock these frequencies on thanks for Ken and Dave for making the MP3 links visible
on the main page there at HPR let's meet download easier now that I'm not using a podcast app
strange how they make things harder on computer and antenna pod doesn't exist on desktop or laptop
whatever all right so yeah very versatile this is just the basic thing so I encourage you to get
this getting our do we know get a kit if you just want to make an Arduino that's activated activated
by you know you can have it activated by PIR or whatever have some walk by and play an MP3
I mean this this thing also have some pretty good prank utility as well like hide it and make
like a really long MP3 and have like scary sounds you know stuff breaking or animals or whatever
or make it make it remote controllable like I said it's not much to spend to it's not much to
spend to be able to use these micro processors and these cool boards and you know get to know
these these little chips by their data sheets and stuff it's a lot of fun and the more you do the
better you get at it so either way you want to go anti aesthetic or make yours actually elegant
you know use use some some boxes that make sense and don't look like garbage either way it's a feature
you have been listening to Hacker Public Radio at Hacker Public Radio does work
today's show was contributed by a HPR listener like yourself if you ever thought of recording
and click on our contribute link to find out how easy it really is hosting for HPR has been
kindly provided by an honesthost.com the internet archive and our sync.net on the Sadois status
today's show is released on our creative commons attribution 4.0 international license