Unsure about which modules to buy

Hello. OpenEnergyMonitor debutant here. Please can I start by saluting this exciting venture, which is exactly what I'm looking for.

My experience is limited to analogue electronics, so my goal is twofold: to learn about microcontrollers and create a home electricity monitoring system. Low cost is not a key consideration. System flexibility is fairly important but so is simplicity. I don't need web connectivity for my system.

I have a few questions, which I hope don't seem too stupid. Please can anyone help?

(1) Energy monitoring node: I'm not sure how the emonTX Shield fits into the suite of hardware offered. If I buy the emonTX Shield plus an Arduino Uno board (the pin headers look compatible), do I get a more versatile(complex?) version of the emonTx? Or does the shield have a different purpose?

(2) I have a hard-wired RJ45 ethernet socket very close to my domestic electricity meter (the socket is wired back to a patch panel and hub). It would be useful to download the energy data to a p.c. on the same home network. What would be the best choice of emonBase?

(3) The emonBase would be located in the same place as the emonTX. Couldn't I forget the emonBase and use a Arduino Uno + emonTX Shield + Arduino Ethernet Shield instead?

Thanks for your help. Apologies if those questions seem to reinforce my ignorance!

jb79's picture

Re: Unsure about which modules to buy


1.) EmonTX is a complete measurement system for 3 currents (0-100A current clamps), 1 voltage, 1 or more temperature sensors and 1 counter (for power meters or other purposes). It only needs a 5V power supply (MiniUSB) and the sensors.

The emonTX Shield needs a Arduino board to be plugged into, so it's no stand-alone unit. There is also one additional input for a current sensors, so 4 total. You can also fit a temperature sensor on the board but I think there is no counter input on the pcb.

2.) EmonBase is not built for connecting sensors directly. It gets the values via an RF module. Maybe it would be a good idea to make a software for EmonBase and EmonTX where the boards can be connected via a short cable (I2C should be possible). I think somebody had the same question some hours before.

Another possibility is to use a Raspberry PI. The raspberry also has got a I2C interface, with modified software for the Raspberry and a EmonTx with no wireless module and modified software it should also be possible to log the values. The Raspberry has also the possibility to log all the values directly, so no additional servr would be needed => very low power consumtion.

3.) I'm not very familiar with Arduino (I'm using PIC's in my projects), but I think that should also be possible if somebody (you?) can modify the software.

rubric8's picture

Re: Unsure about which modules to buy

Many thanks for taking the time to reply.

I think it would probably be best if I start off by assembling the emonTx. As you pointed out, there is no pulse input on the emonTx Shield, and I think that a pulse counter might be useful.

I'll read a bit more about the choice of emonBase to try and decide which one is best for my application.

Thanks again.


Edit 30-11-12:

Just realised that the Arduino itself has a 'counter' input so perhaps you could count pulses and monitor power simultaneously using the Arduino Uno + emonTx Shield


wbortz's picture

Re: Unsure about which modules to buy

I just built a system similar to what you're thinking of, with no RF.  I had an old EeePC 701 gathering dust, so I used it as the emoncms server, and connected a standard Arduino directly to it via USB.  Instead of a shield, I just built the analog input circuitry on a breadboard, and mounted that on the power/analog headers of the Arduino.

There's no ethernet near my electrical panel, but the EeePc is there, and can reach my wifi network,, so that's all I needed.  I carry a smartphone around all the time, so I just use that to check the Emoncms dashboard, no LCD display required.

The advantage for me was that I had the arduino and EeePc already, I only had to add the CT's, 9V AC adapter, and some R's and C's.  Plus, the Eeepc only uses 13 W of power, which is more than a Raspberry (I would imagine), but way less than the old laptop I was using as a sever before, so the total power added by the monitoring system is pretty low.

You can see my public dashboard here:


I'm quite proud of it, and very impressed with this project overall - it was very straightforward to set up.

Only thing about not having an RF base station - I like this system so much, I'm thinking of extending it to another electrical circuit outside that's not on my main panel, and including some sort of water consumption monitor, so I'm probably going to have to setup some sort of RF link anyway in the end.   I'd love to find a cheap wifi enabled setup, but wifi Arduinos cost around $80 each.  The Electric Imp looks nice and cheap and useful, but I don't like the idea of depending on an external internet connection and someone else's sever every time I want to boot my widget.  I'm currently reading up on the nanoderf setup to see if it'll meet my needs.





rubric8's picture

Re: Unsure about which modules to buy

Wade, that is so impressive. Would love to do something similar.

Just out of interest, your public dashboard is showing surges of power above 1kW which last for less than minute. They occur every 10-15 minutes (I looked at the 11pm - midnight data). I wondered what could be causing that...halogen security light triggered by the cat? :D

You made your own analogue power 'shield'. Was there any particular reason to do this rather than using the emonTx shield?


Having read a bit more about it, the Nanode RF seems to be an Arduino + ethernet port (+ other features). I thought that, for a novice's learning experience, rather than buy an Arduino Uno, I could buy the Nanode RF and use it to monitor the LED flash from my Eon electricity meter.

My chief concern is a complete ignorance about the code (willing to learn though). There is a sketch for an Arduino to monitor an LED meter flash at the bottom of the webpage here. Can I use (almost) the same code in the Nanode RF?


arvidb's picture

Re: Unsure about which modules to buy

If I understand correctly, it should be possible to not use a base station at all, but instead receive the RF signals with one of these:


connected to a running server. I saw a note about it in another thread (but I cannot remember which one).

Perhaps someone better informed can confirm if this is possible or not?

Edit: The thread was easy to find, just search for JeeLink:

rubric8's picture

Re: Unsure about which modules to buy

If I understand correctly, it should be possible to not use a base station at all, but instead receive the RF signals with one of these:



Thanks, although that is probably the converse of what I'm trying to achieve :)

I want a base station but not a emonTx.

Is there any reason I can't plug an emonTx shield into a Nanode RF? My electricity meter is right next to an ethernet jack connected to my router so I don't need wireless communication.

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