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EmonTH blinks red 20 times then nothing transmits

I’ve had this emonTH for a long time, at least 2013. It stopped reporting the other day, thought it was the batteries, replaced them twice. The new thing is that it keeps red when inserting the battery then within 5 seconds blinks red 20 times or so. EmonCMS sees the device coming online but with a reading of 0 for both humidity/temp. Anyone ever had that issue?

Welcome back - but I’m sorry to hear you have a problem.

Can you look to see what version it is? You might need to take the p.c.b. out of the case to see. I presume it looks like this
with the white sensor plugged into the 4-pin socket.

Do you have a programmer? If you have, can you connect that and report what it sends to the monitor? If it’s the sketch that I think it might be, with luck, it will print:

emonTH DHT22 example
Node: 19 Freq: 433Mhz Network: 210

(or it might have a different Node and maybe 868 MHz for the frequency)

and then it should print which sensors, the DS18B20 temperature or the DHT22 humidity, it has detected.

This line of code tells you what the problem is:

  if ((DS18B20==0) && (DHT22_status==0))        //if neither DS18B20 or DHT22 is detected flash the LED then goto forever sleep

And it flashes the LED 20 times, exactly as you report.

It cannot detect the sensors. First check for something obvious - tarnish or corrosion or even a broken lead on the sensor. If it isn’t obvious, I’d suggest - but with no real knowledge - that the sensor itself has failed. But it could equally be the processor or its soldering, because both sensors are powered from separate DIO pins that are switched under software control.


Hey the picture you sent is indeed the version I have. My sensor is indeed on 868 MHz. I have a second sensor that is working fine.

Thanks for your reply, I noticed the humidity sensor connectors were just out of place, i reinserted them all and it no longer blinks 20 times but still reports 0.

I took a second look, noticed one of the connectors was still out of place and now success! thanks!

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