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 airFor 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:
https://www.instagram.com/p/B_LeniKgp6X/?igshid=1ap222n2esyunI'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.
