Mostly Dead HeaterMeters

I have 2 that exhibit the same problem...the Pi does not boot when the HeaterMeter is attached. Pi boots fine without it. One of the boards does display No Pit Probe.

Both had been working fine

Any ideas on where to start?

Yah, one at a time! LOL I would pick the most likely board to get running and discuss that board only in one thread. It's confusing enough trying to help troubleshoot one board over the internet let alone talking about two!

I would say the one that shows No Pit Probe would be the best starting point, since it seems to be at least working partially, so lets go at that one....

First question to you is just for curiosity sake... I am wondering how the ATMega got programed in this board if the rPi doesnt boot? Had it booted at one time but not now? or maybe the ATMega was programed previously in another board? I ask because it's good to know the history when troubleshooting....

So, it's booting... GOOD.... It would appear to be working, but without being able to connect and configure the probes etc you are in the dark. So we need to rPi....

How is it that you determined the rPi is not booting? It could be booting but you just haven't been able to connect to it? Do the LED's on the rPi light up?

Lets start there...

1. Both HeaterMeters have been working for over a year.
2. I know the Pi is not booting because of the LEDs on the Pi. The power LED is on but the activity LED does nothing.
3. Unplug the HeaterMeter from the Pi and the Pi boots normally.

My assumption is that there is an issue with the power, but the one board does display the No Pit Probe message which would imply that the HeaterMeter board is functioning correctly.

Ok. well, I'm still confused. First of all, the HM will (should) function on its own without a rPi when plugged into the 12V power supply. (unless you have an older HM?) So if the HM's are working you should see NO PIT PROBE on the display when plugged in (without the rPi)

The way the power goes on the HMv4.2.4 is:

12VDC in from PS
OKI board converts 12V to 5V
MCP1700-33 3.3v Reg converts 5v to 3.3v

OLDER HM's were a bit different, 12v in, OKI to 5V, then 5v out to the rPi, and the rPi would return 3.3v to the HM. There was an OPTIONAL 3.3v regulator on those boards that would allow them to work without the rPi.

In either case, it's 5VDC from the OKI that is getting fed to the rPi...


Pins 24 and 26 on the rPi header get +5VDC from the OKI

Pins 3,5,6,7 are used for communication to the ATMega

and there are a whole bunch of grounds on the rpi header

On older HM's there would be at least 1 pin with 3.3VDC coming back from the rPi


So you should check those voltages and also report what version of the HM board you are using?

Always helpful to plug the rPi into a HDMI input of a tv or monitor to see what is really going on as well..