OpenEnergyMonitor Community

Emontx-shield as solar diverter

Hi all,

I was wondering if someone could point me in the right direction. I have been planning to build a solar diverter for a while now in replacement to my old one.

I have a emontx shield and arduino Uno ready to go. Has anyone done this before? Be an interesting little project.

Question is where would I connect the 3.3V to my SSR for the switching of the immersion heater. The spare terminals appear to be for the DS18B20 sensor.

Any advice or pointer would be much appreciated.



Have you looked at the whole section in Learn?

Robin’s Mk2PVRouter started off as an Arduino build, so there’s a lot of information here or on his website ( that with very little change should get you going.

Both MartinR’s and Robin’s sketches should work with very little change, probably only I/O pin changes.

If you’re using a commercial SSR, first a warning to make sure you have a genuine reputable brand and not a counterfeit one, because there were reports of units bought cheaply that failed quickly or overheated. The second thing you want to watch out for is the input voltage required by your SSR. If you’re using an Arduino, the 5 V logic output on the Arduino’s IO Pins - that’s where you drive the SSR, not from the Shield itself - should be OK for most SSRs.

if you want you can try my version of diversion it works with uno or wemosR3 (uno/wif)-- I used mine for years with out issue …

here a today graph from cooking Easter dinner

if using Cheaper fortek buy one double the rated as the cheaper ones rate there at the amperage they burn at. as that how most chinese stuff is rated the fail volt or amperage


Thanks for your reply.

I purchase a SSR from RS and cost around £30 so hopefully I have removed the risk of any cheap/Chinese duplicates.

Yes I have had a good read through the learning material. I’m am trying to figure out which digital output I need to use for switching my SSR. The emontx v3 uses DI3. But as I am using the emontx shield that one is already in use. Im am thinking DI7. Could someone confirm this please?

Thanks @stephen I have a few spare node mcu’s banging around. What items did you use for the CT and Voltage measurments?



I use the txsheild as well - my diverter is cascading so I use 9,10 and 3 on uno as then I can use pwm.h to adjust to frequency I like… but not knowing what else you are all driving with your uno - the basic empty txshield only uses A0 -A4 all the rest are free to use

i use the wemos R3 which is a combination uno and esp that way i can send info to and from the my diverter

Thanks for that. I will give it a go this week.

I like the idea of using the esp chip but ive already solders the RF chip to the shield. Will your sketch work this the RFM69CW?

I do like the idea of being able to enable/disable the solar diverter. I current use a sonoff relay to switch the 230Vac on and off for my current diverter. I would prefer to do this on the uno control side instead of the 230V power side.

As you can see my current diverter exceeds the solar generated line. My ESS uses PWM to charge my powerwall. It perfectly follows my solar generated line. I want to get the Solar diverter to do the same if I can.



not likely with out alot of modifications – what pins do you use with the RFM69CW if 9 and 10 are free then you can still use pwm.h which makes it more accurate

Best to have a look at the schematic.

To bet honest if it can work as a stand alone device for now I can easily switch the 230Vac and control it via my Home Assistant Automation. I would be happy with that.

Im using a emontx for my logging so I bought the shield for a bit of play time :slight_smile:

yeah it would work and designed to work as a standalone device. it was standalone device for a long time . then I connected an esp to it to send data as daughter board , and the final version that I use now is with the wemosR3 as everything is built in and it eliminated the need for a second power supply for the esp - i could power it from one powersupply but was unstable and prone to stalling - currently with the use of the wemosR3 it has not stalled once in the last year of use – my diverter works best if cascading smaller elements but will work fine if only one larger element just not as accurate if compared to using multiple smaller ones