MicroPython Forum (Archive)

I really like Adafruits Feather form factor.
I really like MicroPython.
I really like STM32F4.
I really like KiCad.


(if someone has a .wrl for the JST-PH connector ...)

This is my first design of such complexity, so I'm looking for feedback.

https://github.com/turbinenreiter/Feather-pyboard

I hope it's OK to use the Feather and pyboard names, wasn't thinking about that until ... now.

• 22ohm resistance between D-/PA10, D+/PA12 is needed.
• I can't find a user switch, it is need for factory reset when filesystem error.
• resistance for D3/D4 is small, LED will be too bright.

Here is my PYB Nano board, it use STM32F401CE/STM32F411CE.

http://forum.micropython.org/viewtopic.php?f=12&t=2514

22ohm resistance between D-/PA10, D+/PA12 is needed.

Will add.

Here is my PYB Nano board, it use STM32F401CE/STM32F411CE.

Do you have a schematic?

My biggest problem right now is finding a small 8MHz crystal.

My schematic is here. We use smd3250 or smd2520 crystal general.

@Turbinenreiter
https://www.digikey.ca/product-detail/e ... ND/2627016

SMD2520 16MHz
https://www.digikey.ca/product-detail/e ... ND/4453827

SMD3225 8MHz
https://www.digikey.ca/product-detail/e ... ND/3125637

So the board came today and it's pretty much dead in the water. Can't get it in DFU mode, can't program it over st-link. There was an error in the power supply, but that is fixed and the microcontroller get's stable 3V3.



/edit: oh man, I just connected a battery and the charging chip burned out. That's the part of the design I took from Adafruit boards and assumed will work.

Turbinenreiter wrote:

/edit: oh man, I just connected a battery and the charging chip burned out. That's the part of the design I took from Adafruit boards and assumed will work.

I just found this thread and I'm delighted that you've undertaken the build!

I too like the feather form factor and have wished for pretty much the board that you are building.

Sorry to hear about the troubles. I hope you're able to figure out why the chip burned and get it working!

Hello again.

I've got your design files open in KiCad to see if I could maybe figure out why your charge controller burned out.

The only problem I see is that when you're on battery power the VDD input on the charger chip is brought to VBAT minus the forward voltage drop of D2. The datasheet specifies the recommended minimum supply voltage (VDD) as Vreg + 0.3V. Seeing as the battery voltage is probably less than the regulation voltage and VDD is a diode drop below that it appears that you're not in recommended operating conditions.

To remedy, I'd place a second diode between your VBUS net and the input on the regulator IC. I'd also put a pull-down on the CE input to the charge controller to give the charge LED current a path to ground and to ensure the charger IC is disabled when your 5V USB power is absent.

I've attached a jpeg of my changes to your schematic for reference.

edit: cropped full schematic to show changes only
edit again: change wording to match diagram