Hi all,

Seemingly my schematic is done (PDF file below). I appreciate any point you mention to assure me it's all correct.

 

no headers? how is this supposed to interface to outside world?
no buttons or jumpers or dipswitches? how do you plan to controlling startup mode?
LEDs with 47 Ohm series resistors? that is asking for massive current from GPIO (25mA-ish).
several hundred of uF across battery?
5V zener across battery? how are you planning on charging the battery?

 

> no headers? how is this supposed to interface to outside world?
Connectors have headers to connect to

> no buttons or jumpers or dipswitches? how do you plan to controlling startup mode?
The device/board is not to be programmed often; mostly it's merely once
I changed my mind a little and connected both NRST and BOOT0 via a cap and resistor (respectively) to GND.

> LEDs with 47 Ohm series resistors? that is asking for massive current from GPIO (25mA-ish).
I'm going to use a LED Red 620-630nm 0805 25mA 60mW (XL-2012SURC) with a 68 Ω resistor for both LEDs in my design.

> 5V zener across battery?
yes, below is from the SIM's hardware design


> how are you planning on charging the battery?
The battery will be charged using a li-ion 18650 (with protection) module connected to it

 

Pardon me. I cannot see any USB connector in the PDF. How to program the board? Please correct me if I am missing something.

 

I saw at least one of them. Just drawn a bit different. NTU21D

 

J3 already gives you 3.3V, SWDIO and SWCLK, so you do have an SWD programming connection.

It looks like pin 4 of J3 is currently unused. I would connect that pin to GND, because the ST-Link and the target board need a common ground reference. I would also consider adding NRST as a separate test pad. It is not always required, but it can be useful if the firmware makes a normal debug connection difficult.

Since NRST is already routed to the reset button, adding a test pad should be easy. With those connections, I don't think a USB connector is necessary just for programming the STM32.

 

J3 already gives you 3.3V, SWDIO and SWCLK, so you do have an SWD programming connection.

It looks like pin 4 of J3 is currently unused. I would connect that pin to GND, because the ST-Link and the target board need a common ground reference. I would also consider adding NRST as a separate test pad. It is not always required, but it can be useful if the firmware makes a normal debug connection difficult.

Since NRST is already routed to the reset button, adding a test pad should be easy. With those connections, I don't think a USB connector is necessary just for programming the STM32.

Thanks for your points.

Below is my new design. Pin4 of J3 is (already) connected to GND and I connected both NRST and BOOT0 to GNd since the device is (mostly) programmed only once.

 

Connectors have headers to connect to

so where are they on schematics? how are you exposing IO pins? i am expecting to see some 2x 20pin

I'm going to use a LED Red 620-630nm 0805 25mA 60mW (XL-2012SURC) with a 68 Ω resistor for both LEDs in my design.

did you read the datasheet for STM32F1? are you sure PC13 can source 25mA? even if it can it is a bad idea. you do not want to stress or load the most complex part on your board, that is job for transistors. same with LED datasheet. what made you pick 25mA? this is just an indicator, not a flashlight. besides,, datasheet clearly says that breaking point (absolute maximum) for this LED is 20mA, so how in the world did you decide to choose 25mA?

and red LED will have Vf about 1.6-1.7V so

(Vgpio-Vf)/If = (3.3V-1.7V)/5mA= 320 Ohm. the nearest common value is 330 Ohm.

below is from the SIM's hardware design
View attachment 370536

ok, zener stays, what about those caps? bypass caps are parallelled to reduce impedance over wide frequency spectrum. so those capacitors need to be different (small, medium, large,...).
the datasheet shows that small value caps are in pF range.the smallest cap you use us 0.1uF.

The battery will be charged using a li-ion 18650 (with protection) module connected to it

that is also not shown in schematics. if this is a BluePillas you call it, i expect to see 2x 20pin. but your schematics shows only couple of pins on J1, J2 and J8.

 

btw, i did not have time to dive deep. comments are only for few things that stand out and i was not focussing on details.... your schematics has no mention of of frequency or Y2 part number (what happened to Y1?). the 33pF may be too large. for details on making STM32 based product you can use reference documents like:
https://www.st.com/resource/en/appl...x-hardware-development-stmicroelectronics.pdf

 

you should have started by posting your own links to datasheets so people willing to help do not have to navigate minefields of clickbait and malicious downloads.
for example R800c datasheet:
https://www.eevblog.com/forum/begin...ue-pill-board/?action=dlattach;attach=2713183

but this is incomplete. for detailed electrical specs you need to keep searching. then you will find that absolute max Sink/Source current is only 2mA per pin. so you should never drive LED directly by some IO pin. that LED on pin 41 is a short circuit as far as R800C is concerned.