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Development Board for the STM32F042

Development Board for the STM32F042

Power output

P4 is a pin header that can be used to access the power supplies on the board along with a generous helping of ground pins. You can’t have too many ground pins on a development board and I find it really frustrating when you receive a board to find it’s only got one or two ground pins. I’ve included four here and another one on the GPIO header.

NPN transistor

The base of the MMBT3904 transistor is connected via a 1kΩ resistor to PA7 so you can control it as a switch from the MCU. The maximum collector current for the MMBT3904 is 200mA. If you need more than that then you should substitute this part for another one in the SOT23-3 package that has a higher rating.


R9, a 100kΩ resistor, pulls the base down to ground so you don’t get spurious switching events during any periods when the gate is floating. The idea is that you connect your load to be driven to the LOAD pin.


All the GPIO pins exposed by the TSSOP20 package are included here as well as the LOAD pin for the NPN transistor and an additional ground pin.

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