Small STM32F103TBU6 Development Board

If you made your own board, post here, unless you built a Maple or Maple mini clone etc
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EntropyWizard
Posts: 15
Joined: Thu Nov 16, 2017 5:03 am

Small STM32F103TBU6 Development Board

Post by EntropyWizard » Mon Feb 11, 2019 7:20 pm

I've been experimenting with the design of a small development board for various projects. This is my latest version for the STM32F103 (and STM32F101) series chips in the VFQFPN 36 6x6mm package. I wanted a 2-layer board with components on one side so it would be cheap to produce and easy to bake at home. I also wanted to see if I could work with QFN packages.

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For programming, the microcontroller ( STM32F103TBU6 ) is nearly identical to the STM32F103CBT6 chips found on the blue pill. The STM32F101 series chips are similar but run at lower clock speeds and lose USB support. The smaller packages lose the PC11-13 pins ( including external RTC support ), VBAT, the secondary SPI and I2C pins on PB10-15, and PB8-9. All available pins are broken out. I put the user/status LED on PB2 since PC13 is gone, and the PB2 pin can be converted to general purpose I/O after boot up.

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The bottom layer is mostly copper ground pour, the ADC lines have a local GND connect, and the analog power VDDA is filtered with a ferrite bead, so the ADC lines should be fairly clean.

I decided to leave off the USB port hardware and simply route A11-12 to the header. In order to support the stm32duino environment, the USB hardware has to be added. I made a "side-car"board to handle the USB power input and data channels. The maple USB reset circuit can also be added. The pins may also be left free as GPIO or to use the CAN bus. This is also useful when using the more basic chips in the VFQFPN 36 package that do not support USB.

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Because all the components are on one side of the board and I added mounting holes, it isn't much smaller than a blue pill, here it is for comparison.

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I've been using an electric skillet to make these boards. The QFN package has giving me some trouble, mostly I think, because I haven't been using a stencil for the solder paste. All the other components have worked perfectly, but I've had to fiddle with the microcontroller with a hot air station to make sure all the pins have good connections.

I modified an earlier version of the stm32duino boot loader and core (Roger's) to support these boards (i.e. LED on PB2), but still need to update to the latest version.

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