Small side project: Teeny Board

Just a small project which i had on my to do list for quite a while: a devboard smaller than the maple mini.
Because i didnt had the need for every GPIO Pin, so i wanted to make something like the size of a Teensy (you can guess where i got that name from ).
So in short:

• STM32F103R- Series with a 8Mhz external crystal (though no RTC Clock, no space)
• 0.3/0.6A LDO
• Peripherals
  • 9 Pins connected to an ADC
  • 12 Pins connected to a Timer
  • 3x UART
  • 2x I2C
  • 2x SPI
• In total 21 GPIOs broken out
• Should be running the STM32Duino Bootloader
• 1 User LED
• RTC Crystal can be added later on
• aswell as RTC Battery
• USB 5V and the Power Input can be seperated (just like on the teensy)
• And a Reset Button
• Same size as an Teensy 3.2

I’ll maybe try it out when i order some PCBs next time and find some space on the PCB.

Github Repo

I maybe could fit 2 or 4 more GPIOs on there if i would find a smaller button and crystal, but that design is already madness for 2 layers. And i already had to sacrifice some caps from the MCU, although there are already so many around, and the traces aren’t like 2km long, so dont think it will make any big performance issues.

(Yeah, got too much time now. And have to still wait like 3-4Weeks for everything to arrive from china for the 3DP. Controller)

~Straw

Very nice

Did you consider making it like the digispark with the edge of the board as the USB connector ?

Neat, I like it

Looks nice – I like it.

The pins on right, are they for SWD?

@RogerClark would love to use the pcb as the connector(or make something breakable so you could remove it if you want), but besides the enig plating which would be necessary to use it more than 10 times, the pcb would have to be thicker, 1.6mm isn’t enough and 2mm costs already 16$ more (2.4 or so would be ideal).
So well, would be nice to use it as an usb dongle, but a microusb port seems to be the cheaper option :/

@C_D thanks:)

@Ollie no, they are additional gpio + power and bat backup for the rtc. Swd is only available through the two pads on the bottom :/

4AM, i really should get some sleep

~Straw

@straw

Thanks for the information about the PCB edge connector. Shame it costs so much extra

I have seen designs on standard PCB stock, where the edge connector is shimmed up to the correct thickness for USB with an additional thin plastic shim epoxied on the back of the board (some of the el-cheapo USB LED “torches” use this trick). It is however an extra manufacturing step, so possibly too much trouble.

For DIY use a bit of electrical tape does the trick

Not really suitable in a commercial product unless you are selling only on ebay…

@C_D hm…yeah, that sound good enough for me
OK, i will try to add the edge connector.

~Straw

Personally I prefer the micro USB socket. The edge connector is only useful for programming, where as a micro USB can be useful on the final device if the project is some kind of USB device.

@C_D im actually planing to make the edge connector snap-able, so that the micro usb connector is then available.

~Straw

That is a very nice little board! I like it.
Is it pin-compatible with a Teensy 3.2?
I would also prefer the micro-usb socket because it is easier to plug with a standard smartphone cable.
I assume that the MCU is pin-compatible with other STM32 so a F303 version would be nice, as seen here: viewtopic.php?f=40&t=893

@rreignier no, it isnt pin compatible with the teensy nor compatible with the 32f303.

For the first part: its too hard to route the pins around that they would be pin compatible on such a small board.

For the last part: it would be easily possible to change the board that it would fit a 32f303, but it wont be possible to make one board for multiple different microcontrollers, because the f1 and f3 series differ in their power pins on some points. And there isnt space to make it fit

@strawberrymaker Thanks for the quick answer and the clarifications. Interesting.