Create 2024-09-19-stm32devboard.md

_posts/2024-09-19-stm32devboard.md

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+layout: post
+title: "Low-Cost STM32 Development Board"
+image: /images/STM32devboard/F072thumb.png
+---
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+I am using STM32 microcontrollers more and more for work and personal project, and couldn't find an off-the-shelf development board that satisfied the following requirements:
+
+- STM32 MCU
+- under £10 each (ideally closer to £5)
+- simple schematic
+- easy mounting holes
+- CAN bus compatible, with onboard transceiver
+- USB-C
+- CAN bus and USB concurrently
+- flat bottom / single sided
+- easy to manufacture (e.g. JLCPCB PCBA)
+
+When talking to someone about another recent PCB I'd made (a USB slider with a SAMD21), the STM32F072 came up. I looked through the datasheet and saw that it had USB and CAN, and unlike a lot of the smaller/lower cost STM32s, they were on separate pins! This means I can use it as a general purpose board for reading and writing CAN bus messages over USB.
+
+I designed a simple development board, with two rows of GPIO, a boot button for STM32 DFU mode (for programming), USB-C with CC resistors, a 5V to 3.3V regulator, a CAN bus transceiver (with pads and termination resistor jumper), and SWD programming pads on the rear. Although not ideal for all applications, USB and CAN on this STM32F072 can also work crystal-less, so there is no additional external clock - this reduces cost and complexity.
+
+Although I used standard 2.54mm spacing for the pin headers, the PCB and mounting holes are all metric. Many development boards from companies like Adafruit are designed in the USA, they instead use imperial sizes for the PCB outline and moutning holes. Not a huge issue, but it's nice to not need to use inches when mounting this to things.
+
+<img src="/images/STM32devboard/F072photo.png" alt="" class="inline">
+
+Although the board functions with no issues, I did start to run into speed/memory limitations sooner than I would have liked. For simple or low power requirements, it'd be perfect and it's hard to argue with the price. However, I decided to swap the F072 for a L433, which (seems!) pin-compatible with the F072, but has about 2x the clock speed, and 4x the memory.
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+<img src="/images/STM32devboard/L433_3d.png" alt="" class="inline">