RPi 4B not booting after SPI connection

[tomasveiga]

Hello,

I have a Raspberry Pi 4B and was trying to get data from a Hall Effect (A1391) sensor using an ADC (AD7689) connected via SPI. I've put below the datasheets and the connection schematics between the ICs and the RPi.

Hall effect sensor A1391 : https://documentcloud.adobe.com/link/tr ... e88ab153fe
ADC AD7689 : https://www.analog.com/media/en/technic ... 2_7689.pdf

HE-ADC-RPi.png (24.45 KiB) Viewed 558 times

So, I've never actually managed to get any data from the ADC, probably problems both with codes and proper enabling of SPI connections. Anyway, the real problems started a few weeks ago when I plugged in the RPi and smoke came out from it somewhere between the power port and display ports. As soon as I noticed the smoke I quickly switched the plug off and disconnected everything from the RPi. I re-wired the whole circuit again (even though no problems had happened before) and turned it on again. It went back to work.

Never happened again until last week when smoke came out again. I did the same I had done in the past but this time it didn't fix the problem. Eventually, I turned the RPi on with nothing on the GPIO pins and the green LED finally turned on but very feebly. I managed to connect via SSH but only for a minute or so before the green LED went out, but the red always on. Since then, the RPi does not boot, lighting only the red light when plugged in and the green light never shows signs of life.

I assumed I must have done something wrong as I am fairly new to RPi but I can't find exactly what went wrong. If anyone has any idea of what might have happened, please let me know!

[Botspot]

Were you powering the sensor using the 5v GPIO pin?
If so, I'm surprised your Pi lasted that long. If you powered your sensor with 5v, then it will communicate with the Pi using 5v pulses. The 3.3v-based Pi has a problem with that.

[tomasveiga]

Thank you for your answer but I powered the sensors using 3.3V

[Burngate]

... and smoke came out from it somewhere between the power port and display ports
Never happened again until last week when smoke came out again.

Smoke is Bad.
Your description of where it came from appears to be the power management chip, which converts the incoming 5v to all the supplies the Pi needs.
It's slightly surprising that it survived one episode of smoking

There doesn't seem to be anything wrong with your schematic, so quite possibly you didn't wire it according to your schematic.

One thing that you could do is measure the 3v3 pin - it won't help you resurrect the Pi, but it may tell you more about what happened.