I’m trying to use an RPi Pico W as a temp/humidity sensor using a DHT20.
It kind of works - at least sometimes, but I keep “losing” sensors more or less randomly.
I connected everything up like here (using MicroPython): https://github.com/flrrth/pico-dht20 There are currently 4 sensor-boards, 3 soldered, one on a breadboard.
The error modes I could observe are:
-
DHT20 fails to init - sometimes after the first read, sometimes after days. Resetting the machine works sometimes, if not, power cycling usually does the trick
-
The board just “stops” after about 5min - the serial console just says “device disconnected”. Power cycling is the only option.
My measurement work by having a timer fire every minute, connect to wifi, read from the sensor, and then send an mqtt message (either the values or an error message) and shutdown wifi again.
My current ideas why it could fail (but I’m not an electronics guy at all):
- There is some kind of “rogue current” messing with some IC.
- Some component is broken
- Maybe the power draw is too low or issuing sleep() messes with the USB-power connection somehow?
For me the problem is, I don’t really know where to look for errors. The software works in principle, the soldering seems to be good enough to sometimes work for days, and looking too deep into the whole electronics side is beyond my capabilities.
Perhaps slightly adjust your logic a little and see what it does.
Read from the sensors first, then enable and connect to wifi, send the data, then disconnect. That would reduce the maximum power draw as only one function is active at once.
Small edit: I have a MagTag ESP32 board with circuitpython that can't read onewire devices while the wifi is active. Whether that's because of supply instabilities when wifi is transmitting, or interrupt conflicts, or just plain poor programming in the onewire drivers or the wifi drivers, I don't know. But reading the devices first and then connecting to wifi and sending the data afterwards works.
I tried that. The loop was:
- Read sensor
- Prepare message
- Wifi on
- Send message
- Wifi off
That should nicely separate everything, but it still ran into similar issues.
I had something similar happen in one of my ESP8266 projects (also running MicroPython). What I wound up doing was, every five wall clock minutes (maybe a bit sooner than that, for your case) I had my firmware do a
local_networks = wifi.scan()just to exercise the wifi functionality. If that failed I have the code dogc.collect()followed bysys.exit(1), which causes the 8266 to reboot automatically.Give that a try.
I'll give it try!
Do you have any idea, what's causing the issue? Is it specifically the scanning part that's relevant here? I'm starting/stopping wifi each minute, so the chip shouldn't just idle around all the time.
No, I don't. My best informed guess is that the wifi connection's state machine gets stuck once in a while, it misses a couple of packets, and then sits there doing nothing. So, by kicking it a little it doesn't get a chance to freeze up.
