Hi Guys,

Before I try and return my EmonTH I just wanted to check I ma not missing something.

I bought the EmonTH assembled from the shop along with other kit. All the other kit is working as I expect.

I powered up the emonTH with a pair of AAs and the red led lights but then never goes off. I have also powered the unit from my serial connector and watched the serial monitor but I get no output.

Do I have a dead emonTH? is there anything I should be trying or should I just return it and get another?

I can find very little about troubleshooting this but the guide says it should go out or flash. I have tried powering with and without the humidity sensor plugged in.

I get none of this just a solid LED:

Once batteries are inserted into the the emonTH (we recommend rechargeable alkaline or low self-discharge NiMH for best performance to environmental impact) the red LED should light up for a few seconds. During this time the emonTH will attempt to detect any connected DHT22 or DS18B20 sensors. If any sensors are detected the LED with extinguish and the emonTH will start transmitting readings every 60's. If the LED flashes several times this indicates that no sensor has been detected.





Schism's picture



To rule out firmware issues, you could try uploading the default firmware again (here), or even a simpler sketch like this one, which should provide output from the DHT22 (same folder contains a sketch to test the D18B20).

Do you have the IDE set up already? If not, I found the instructions were fine for me.



BioGuyver's picture


Hey Schism,

Thanks for the heads up. My experience with Arduino and the IDE are limited and for some reason I expect some sort of output on the serial monitor.

I downloaded all the git sources etc and re flashed the emonTH and it started responding as it should. So not only is it working as it should be but it was good experience as well.


Thanks for pointing me in the right direction.



Schism's picture


No problem.

You should get serial output from the default sketch; make sure you are on 9600 baud and that you pull the batteries, plug in the UART and it should give you something?

On mine, I do get corruption in the serial output very often - odd characters suggesting there is some loss and/or encoding mismatch. My advice is to feel free to add extra integers to the rf payload within the sketch, and then view them in emoncms for easier debugging (especially in-situ).

You can literally add a further int, upload the sketch and within a few moments you'll find the int displaying in emoncms' input list... can be very useful.

BioGuyver's picture


Hi Schism,


Sorry i missed this reply as the email alerts were off for some reason. Have fixed that now.


Thanks again for the info, I have serial output now from all the devices when I am testing and I am getting more comfortable with the editing of the sketches to test things too.


Thanks again


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