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 (Over-engineered) Thermal Detonators! [Lights + Sound + USB recharge]

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Recent Updates! I've finished revision 2.1 of the circuit board, which is smarter and has sound, scroll to the most recent replies for details!

Update - 4/21/20: The main board is complete, and features lights, custom sounds (and music) from an SD card, and USB fast charging. See the latest post for details.

There is a short video of it making sounds on my Instagram:

Will try and document the finished project better once the ball is painted.

A bunch of friends at a recent armor build party asked about making some thermal detonators, so I hunted for a 3D model, had a look at the electronics, and decided to over-engineer them For Science! I'll post the build log here because I'm pleased with the work so far. The base of the model is the fantastic Oubliette model on Thingiverse, remixed to house the circuit boards and battery.

After expending a majority of brainmatter designing my Sabine gauntlet to do some fun things, I decided it'd be neat to have it remote trigger the thermal detonators, so the one I'm posting here is the first revision of my Fancy Boom Ball. The current schematic (which I'll probably post when it's finalized along with the remix of the models and such) supports some pretty basic but fun and educational features:

  • Wireless triggering from a gauntlet, detonator prop, or trigger via the normal method using another Very Satisfying Button
  • USB rechargeable LiPo cell that hasn't yet caught fire, or 2 AAAs
  • And of course, the three blinking lights, and a red light on top.

A future revision might swap the old 1990s style circuit with some modern chips to support sound and impact reaction. This was mostly an educational project for me to try out some new manufacturing techniques and actually build something.

Anyway, the fun bits:

Frist, we print, and grab a delicious cup of boomspresso:

Then, acquire one of the PCBs!

This was actually the best part, because I always wanted to design a schematic and turn it into a real PCB, which is super easy to do now. This board controls the wireless trigger and contains the power regulation stuff. All the blinky lights are getting ordered soon, but I wanted to get one circuit ordered first so I can see if there's something I'd want to change. Which, there is, SMD soldering isn't scary, so I might refine the boards to use more SMD/SOIC components instead of the bulky through-hole components, but then this becomes harder to make as a kit :thinking:...

Where the story ends today: Batteries!

Today I got the small LiPo cell, and did a test fit to make sure it'll work under the main circuit board, and to ensure that the battery charging module doesn't set things on fire. (It did not, in fact, set anything on fire. After reversing the polarity of the battery connector--Adafruit has a thing for switching the battery polarity so that generic LiPo cells explode. Probably good for business. Always pay attention to polarity!)

The last bits of effort is finalizing the schematic for the lights and button and switch, and ordering that PCB. It plugs into the top of the RF control board to get power and the activation signal, and since this board mounts on top it also contains the USB port to recharge the battery. Overkill for something so simple? Yeah probably, but I'm learning a lot on this small project so I don't make simple mistakes when building my much more complicated gauntlet.

I'll update this with some more progress once I return back to the boom ball.  :sabine:

« Last Edit: Apr 21, 2020, 05:11 AM by MauAbata » Logged

Druj Jes

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Re: (Over-engineered) Thermal Detonators! [WIP]
« Reply #1 on: Jul 18, 2019, 08:55 PM »
This is awesome! I can't wait to see the final product.  Watching with great intrigue.

Druj Jes - M.M.C.C. #2302 - B.O.M.B. #105 - M.V.S. #105
Re: (Over-engineered) Thermal Detonators! [WIP]
« Reply #2 on: Dec 04, 2019, 03:08 PM »
Can you explain what its going to do? It looks epic and I cant wait to see it done!

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Fenrir Kyramud

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Re: (Over-engineered) Thermal Detonators! [WIP]
« Reply #3 on: Dec 06, 2019, 01:41 PM »
I have a couple of these boomers, printed, painted, weathered and awaiting electronics. I'll be following this thread closely.

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Re: (Over-engineered) Thermal Detonators! [WIP]
« Reply #4 on: Dec 10, 2019, 12:27 AM »
Extremely cool idea, vod!

Re: (Over-engineered) Thermal Detonators! [WIP]
« Reply #5 on: Mar 12, 2020, 02:46 PM »
So, I've been busy on Sabine  :sabine: and haven't had much time to revisit this, BUT:

Can you explain what its going to do? It looks epic and I cant wait to see it done!

The current circuit I posted last time was a power supply and radio receiver, based around a Holtek HT12D decoder (similar [exactly?] to what is in remote controls, etc). The idea there was it'll receive a signal from my gauntlet to activate the thermal. A neat party trick when I tell people "here hold this" and then start them flashing.

There's another circuit that goes on top that handles the LEDs and switches, though I didn't get around to posting it because I (for shame) made a really annoying wiring error when I had the PCBs made, and it arrived not so very functional. It's almost a year later, and I've gotten better at this. (Better = I'll post another thread someday showing the bodge wires and hot glue that got my Sabine gauntlet working in time for C2E2 2020).

One thing I had in mind when I started this: Nah, I'm not gonna use a microcontroller, I can do this with discrete logic.

Yeah, sure, I can do this with discrete logic. The current form has a pretty hefty weight to it in through-hole chips and extra stuff'n'things, and it's awesome! ... Awesome here meaning "for academic purposes only and not actually practical".

^ So that's the mess as it was when I tossed it in the great box of "refactor later". The chips on top are a timer circuit (ye olde 555), some counters and comparators, and a mis-wired set of gates that was supposed to create a on/off latching circuit. Essentially, it's hardwired to step through a given sequence of lights, and it does that correctly if I just add a few blobs of solder here and there. Oh, and a USB plug to charge up the battery.

As for the radio receiver, that uses a system compatible with other props I've been working on (helmet fans, my Darksaber blade, etc), which in this case lets you say "turn on/off" to the prop. Fun, but this is not the way.

Over Engineered Thermal Detonator, MKII:

Okay remember when I said "no Arduino?" Someone, step back in time to 2019 me and tell them that Arduinos are in fact The Way. Maybe not jamming an Uno in there, but I'm currently reworking the circuit to be better, smarter, and (strangely) less expensive. Pics soon, once I pry it off the breadboard and get it onto a PCB with my beloved Phoenix Squadron symbol painted on.

I'm currently working in support for:

  • Wireless activation, 2-way, which also reports battery stats (other sensors?)
  • Less discrete logic, more Atmel magic.
  • SOUND! (This is ruining all my plans of using a tiny atmel, but dagummit I'll get it)
  • I'm honestly adding a vibrating motor for that extra "AAck!" response when I set it off in someone's pocket.

Anyway, I'll update as I proceed. See you next year! (hopefully sooner)

Re: (Over-engineered) Thermal Detonators! [WIP]
« Reply #6 on: Mar 17, 2020, 12:52 AM »
Smaller update, bigger changes:

I got the sound and lights and everything prototyped on a breadboard, and moved on to making another, better circuit board. I'm currently re-designing the 3D model for the prop, since I need a few extra holes in places holes did not exist.

But hey, look at this fun pile of soldering I've got coming up!

It took forever to make just the bottom half of a ball. But, I'm leveling up my Fusion 360 skills, so that's sweeet. Have half a boom-ball, with some allowances made for 3D printing (mostly, bigger grooves to keep them visible after sanding/filler primer/whatever else gets gunked on. Originally, I used the Oubliette's model, but with the changes to support a speaker and such, I figured it'd be better to start over from the ground up. And, if anything, it's One More Model that exists for people to print:

So for curious minds: This circuit board is 58mm wide, with the idea that it'll fit in the center (just above or below the lights) of your boom-ball (mine measure 60mm at the helf-way point.) SD and USB connections are accessible through the ring. Half of my brain wants to find a clever way to hide all that, the other half thinks it'll be okay. It's in the back, anyway.


PS: If this thing actually works (it really mostly works now), I can provide a DIY "get this stuff on amazon and shove it into your boom-ball" version with tiny arduinos and modules and stuff. It's fun, blinky, and educational! I have videos of the breadboard version doing stuff, I'm just not 100% sure on where exactly to put them.

« Last Edit: Mar 17, 2020, 12:56 AM by MauAbata » Logged
Re: (Over-engineered) Thermal Detonators! [Almost Ready!]
« Reply #7 on: Apr 17, 2020, 07:35 PM »
It's alive!

Well, almost. I ordered an incorrect component so the SD card reader isn't working right, but overall, the new design has been somewhat finalized and I'm working on wrapping up the model for the shell. New components will be here Tuesday (4/21) so I'll have an update then with it blinking and hopefully making sound. By then, the shell should be done, too.

Meet the new PCB!

This is my most complicated circuit board yet, but it's so satisfying. This is almost the same amount of bits going into Sabine's gauntlet, sans an LCD display and keyboard. Above is the blank board, which I got from JLCPCB.

Soldering round 1, hot air

For tiny surface mount soldering jobs like this, I've been enjoying my hot air station. This time around I bought a solder paste template to try and get a precise gloob of solder paste on the board, but my jig was janky so it made a mess. I'll film the assembly for round 2 with a proper solder paste application, for curious minds. Solder bridging happens, check out these massive lumps!

Soldering round 2, so much flux.

Getting rid of the solder bridge from the hot air / reflow method is pretty easy. I've got a tube of flux that I just gloob all over the legs, and drag the iron over them to separate out the solder blobs. Clean the tip between each drag (those brass wool ball things work awesome), and go again. Solder in flux flows toward heat, so if you have a larger pad it can be helpful to drag more on the pad so you pull the solder globs down the leg of the part. Here's the result, bathing in a flux bath:

Fitting into the shell!

And with that, the first prototype is ready to fit into the shell! The crystal is a bit too small, and I overloaded it by getting 22nF caps instead of 22pF, so that's been replaced with a ceramic resonator for now, as well as a pull-up resistor removed from the SD card buffer IC, since the IC I used in my schematic has an invert enable pin, and I bought the one without the inverted enable pin. Boo.

That said, the microcontroller accepts programming and runs through the startup sequence, but doesn't get past the SD card check and halts. That problem will be fixed when the new parts arrive.

What's Inside?

In the picture you can see it charging up the LiPo cell from USB. There's a handy charge indicator out the bag, plug in until it turns green and you're good to go. For the other features, assume we're looking at this thing with the USB port to the top:

On the top right (1:00-2:00 position) is the SD card, which holds sound files for playback during various states of the prop (startup, loop, shutdown, etc.). There's some easter eggs, as well as music files, since the speaker on this thing is actually halfway decent.

On the right (3:00-4:00 position) is a mono class D audio amp, a teeny little volume knob, and a reset button. The speaker plugs in to the bottom side of the board here.

At the bottom (5:30-6:00 position) is the iconic 3 LEDs for the front of the prop. These are soldered in at an angle to fit into the holes in your kaboom ball. There are also a few pin headers there--the long single row by the reset button is UART for use with an FTDI cable for serial debugging, the 2x2 pin header is the connector to the top shell of the prop, which connects the lever, red lamp and pushbutton.

The bottom left (6:30-8:00 position) is just power management stuff for the microcontroller. It's overkill, but there's a voltage supervisor to ensure the micro stops if the voltage levels get weird, and to ensure it delays bootup until every other component settles. I figured this is good, since the power amp can cause some voltage fluctuations and if the worst case happens, I don't want the microcontroller to spew garbage onto the SD card. It did this when I was breadboarding it, and I wasn't a fan.

Left-to-top (9:00-12:00 position) is all power management. There's a 3v -> 5v boost converter, a 5v -> 3.3v linear regulator for the SD card + wireless module, a charge controller for the battery, and some logic to switch power sources between battery and USB/FTDI/ICSP.

Pin headers in the center are for ICSP programmers to program the microcontroller, analog sensor hookups, and some pins reserved for the wireless transceiver module. Remote detonation? Yup.

That's it, see you Tuesday!

Thanks for stopping by, let me know if you have any curiosities, and I'll be sure to update when the new parts come in to finish this.

PS: Speaking of tiny circuits with essentially an Arduino living on them, I've got a couple little boards that function as helmet fan speed controllers or programmable light sequencers, that's what's in my darksaber. I can nerd out about those, if there's interest. Waiting for a squad member to get back to me on the whole fans-in-a-helmet thing.

Update - 4/21/20: The correct IC arrived, and a proper crystal, and they both work right away! Every feature is working now, and I only have a couple tiny things to sort out before I can sell boards and post tutorials.

I have enough parts to assemble one more, then I'll need to order more chips. I've got 5 boards of this one, then will reorder the final revision once those find homes.

Current operation is to slide the lever to arm it (plays activation sound and flashes red light) then push the red button to start the countdown. A long press of the red button goes back to quiet armed state, and closing the lever disarms it.

Double clicking the button plays "Tobe, Gundam!" for some reason, but that will be changed.

There's a video of it making sounds on my Instagram:

I'm going to wrap up the 3D model tomorrow and paint that, then I'll have both the finished balls and just the board up in Etsy and maybe here in the swaps forum if it's a good idea to do so.

« Last Edit: Apr 21, 2020, 05:08 AM by MauAbata » Logged
Not sure if this warrants a new thread or not, so I'll tack it on here. But first, some updates:

They're done! The first run is ready to go, details over in the sales forum.

I'm working on making a glue-in mounting harness that fits most* 60mm shells, specifically designed for The Oubliette's shell:

Since The Oub's shell doesn't have any speaker cutouts, I'm going to flip the speaker to point it up toward the circuit board. There really isn't a decent way to make a sound enclosure, but over-engineering at this point is a moot point. We're dealing with 22kHz mono PCM audio, I'm pretty sure the phrase "out of phase" is a consideration I should leave behind.

There's one problem, and that's the pushbutton. Some extra features of my sound board (battery level, disarming, etc) are activated by various button presses on the red lamp. The Oub's shell, as with most others, don't actually have a button there I don't think. So, I'm going to adjust the software to disable those features and go straight to counting down when you open the lever, if the prop is powered on with the button held in. For props that don't have a button, bridge that connection with a jumper for lever-only functionality.

I need to gauge interest here to determine which prop to continue (I also want to work on the wireless fan control). If you're interested in the adapter bracket for an Oubliette or similar shell, post a comment below. This would be sold as a kit, including board, lower harness, speaker, and upper harness with battery.

I'm working on another variant for the lights-only option, but I haven't made the production run for the lights-only boards (I'm currently repurposing another board, but this isn't it's final form.)



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