Moo Bug

Fluffbug, but with a Pi Cow

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Some time ago I decided that the SAMD21 chip I originally used for the #Fluffbug is not powerful enough, and impossible to get anyways due to chip shortage, and I identified two options I could go with, ESP32-S2 and RP2040. In the end I went with the Lolin S2 Mini board and the ESP32-S2 chip, but I never stopped thinking how would the things go if I went the other way. And then the Raspberry Pi Pico W board was released, adding WiFi to RP2040, and it became even more tempting to try it with the robots. I resisted several months, but eventually caved in, and this is it: Moo Bug, a Fluffbug with a Pi Cow ("pico w", get it?).

  • The OLED Face

    deʃhipu12/30/2022 at 23:09 0 comments

    The PCBs arrived right after the holidays, and I quickly assembled one, moved the whole legs from one of my fluffbugs, and here it is, all working as expected. I just had to update the pin names in my circuitpython code, that's literally it. But then I decided to try and get to work one of the shields – the one with a display and a speaker.

    The display just worked. I used the SH1106 library for displayio, and I just had to rotate the display 180° and add a 2-pixel horizontal shift to adapt it to this particular display. I got really good with that working on all those handheld game consoles.

    The speaker turned out to be a bit more challenging. I used a MAX98357A I2S amplifier, because I had that on a module earlier and I was confident it works well. Well, despite the schematic being practically the same with the module (minus some unnecessary caps, as usual), this one didn't work. The chip is a bit small QFN package, but visually it looked soldered well. I tried a lot of different things, until at fifth re-soldering of the chip with the hot-air gun, it suddenly started working. I suppose looking good is not enough. Of course with such a tiny speaker the quality is questionable, but it does sound properly robotic, and it's surprisingly loud (I hardwired the amplifier to maximum gain).

  • The PCB Design

    deʃhipu12/30/2022 at 22:53 1 comment

    This is my first project where I completely switched to EasyEDA as a PCB design tool. I honestly tried KiCAD several times over the years, and it's just so hilariously bad at exploring designs, that I gave up on it. EasyEDA is still far from ideal (especially the copper fills), but it's not completely unusable.

    In any case, I followed up on my fluffbug work, of course, but I made everything except for the battery holder surface-mount. I found some pretty nice low-profile smd female headers on LCSC, and the IDC connectors for the servos also exist in SMD versions. This actually gives me much more room on the PCB, because headers no longer take up both sides.

    There are still a few pilot holes for all the components, so there was some work squeezing it all to fit, but in the end it came out rather compact. Since the headers are double-row, I can use them to add bigger "face" shields for the robot, with things like displays, cameras, sensors or speakers. In fact, I went ahead and designed two shields, one the size of the pico with a camera, and one bigger, with an oled display and a speaker.

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