Analog input (0-10V / 4-20 mA) with emonPi or emonTx

Hi everybody,

I am looking for the simpliest way to measure solar radiation using an emonPi or an emonTx (I use them for other measurements).
I already own a solar radiation sensor (Tritec Spektron 320), which :

  • has got 4 possible signal outputs: 0-10 V, 0-3.125 V, 0-150 mV, and 4-20 mA
  • requires a 5-30 Vdc or 12-30 Vdc supply voltage (depending on the chosen signal output)

In the second hand, I would also ideally like to connect the sensor through a wireless connection, as it is installed outdoor on the roof of a building (wired connection is strongly complicated).

I guess there are many ways to reach my 2 goals (1- getting signal and 2- through wireless connection), but as I am a newbie in electronics and IT (and sadly don’t have much time to learn because of professionnals activities) I really need to find the simpliest way to succeed…

Thanks a lot for your precious help !

Neither emonPi nor emonTx have a built-in connection for an analogue d.c. voltage. One is present on the RJ45 connector, but using it will mean you need to modify the sketches (and that’s slightly harder in the emonPi because updates will ordinarily restore the sketch back to the default). But if you get over that problem - it’s possible but you need to remember a different procedure each time you update your emonPi, it is probably the simplest. You don’t have the same problem with updating the emonTx - that is completely under your control.

So the easiest is your emonTx. ADC6 is available on the RJ45 connector on pin 8, and GND on pin 5. Connect the 3.125 V output to those (positive to pin 8). In the sketch, you must remove all references to Analog input 6 and digital pin 20 (in the standard sketch, D20 switches power to the temperature sensor, so you can no longer do that) and add a few lines to set Analog Input 6 as an input and to read the voltage. The full scale (1023 counts) is 3.3 V and so you will never reach that (you should only ever get to 968), but it is close and easier and probably more accurate than using the 10 V output and dividing the voltage down. What you lose on resolution is insignificant.

If you go to wireless, then I’d suggest looking at Martin Harizanov’s website. I don’t know details, but I suspect he has something that would connect directly to your sensor and feed the data into your emonPi using the same radio channel as your emonTx.
If a direct cable connection is hard, then this will be the better way.

Thanks a lot for this precise, fast and useful answer Robert !
I had a look on Martin Harizanov’s website, I found the BBoilRF system he developed, it’s RF temperature measurement, but apparently no possible application with every type of analog sensor…