encounters with electron•ics / by flabbergast

The bat board - a breakout for STM32 in LQFP48

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I like the size of the ARM Teensies, and I’ve seen (and tried) a STM32L4 breakout of this size here: Dragonfly. However I wanted something cheaper, simpler, and hand-solderable (as usual). Hence a breakout board I dubbed “the bat board” (because I’m not good with names).

It accepts STM32 chips that come in LQFP48 package. It was designed for STM32L052CxTx, but any pin-compatible MCUs should work (ST is good at that). So far I’ve only tested the abovementioned L052, but at least F072 should also work.

I should also say that the design was also influenced by mchck - but the STM32 MCUs usually have some bootloader in ROM, so it is easier to solve the chicken-and-egg problem.

Board features:

  • one LED (on PA15, active high), one reset button, one boot/user button (tied both to BOOT0 and A1). {This is not ideal, the next revision will have a solder jumper to disconnect from BOOT0.}
  • micro USB on the appropriate pins
  • NCV8170AXV330T2G 150mA voltage regulator (ultra low quiescent current)
  • solder jumpers to disconnect various power nets, so the board can be powered from USB, or from a battery (chargeable from VBUS) through a regulator, or bypass the regulator entirely.
  • footprints for an optional ferrite bead and another capacitor for VDDA, to make it more analogue-friendly
  • footprints for a high-frequency crystal (required to have USB on F1 or L1 MCUs)
  • one-sided (for some toaster oven fun)
  • PCB heavily annotated (so that I don’t have to dig up the docs on the computer all the time :)

Note: the next revision (rev2) will rearrange the power pins around the micro USB connector, to make it compatible with Teensies, so that one can use already existing battery charging ‘add-ons’.

Sources

  • the kicad sources are here
  • PCBs are orderable from OSH Park
  • I’ve modified Black Sphere Technologies’ DFU bootloader to run on this. Works, but very slow. The sources and docs are here, and a compiled binary provided here.