I've discussed this topic in the Covid area, but we can't get to the bottom of it, and it seems to be a specific Every issue. Apologies to those who participate in both areas, I'm closing the other thread.
I am developing a CO2 monitor for classrooms. My setup works with a Nano Every, and connects to an RTC, a microSD card reader, a DHT22 temp/humidity sensor and three CO2 sensors. That works well with a USB power source. When connecting a 9V walwart to Vin and Gnd it all works except the DHT22 sensor. I replaced the sensor, no change. I measured voltages and get 4.8V where I expect 5V and 3.28V where I expect 3.3V.
An advise was to replace the 9V with a +5V/Gnd pin to a 5V regulated power supply. No change.
I was asked and tested without the CO2 sensors connected, a very good question, for an unexpected reason. The short answer is "yes", the DHT22 sensor works without the CO2 sensors. But I noticed that when I switched from the 5V power supply to the USB that the non-functioning temp sensor would remain non-functioning. It would come on after pushing the reset button on the Nano Every. So I wired all sensors up again, runs fine from USB (no surprise). Swap to 5V and the temp sensor reports 0. Reset button once: same zero result. Reset button again: temperature reading is working.
Reset button again: good temp reading.
Power cycle: zero reading. Reset button: good temp reading.
Power cycle, with 15 seconds wait time before reconnecting: zero reading. Reset button: temp ok
Power cycle, with 2 minutes wait time: zero reading. Reset button: temp ok.
My question: what is different in the power-up process when using 5V as opposed to USB? Or am I overlooking something?
Thanks for all suggestions, Hubert