Raspberry Pi Emon Shield


I'm new to OpenEnergyMonitor but I quite like the project. Whilst exploring the site I had the idea of a direct RaspberryPi Emon shield without taking the diversion through a RFM tranceiver pair.

Where it has advantages using a wireless transmitter if multiple measurement boards are required IMHO it just adds complexity if only one central fuseboard needs to be monitored, let alone the additional power consumption and RF air pollution.

Unfortunately I didn't find a lot about this, maybe it has already been discussed in the forums.

When I talk about a RaspberryPi shield I'm thinking of a AVR powered (Arduino compatible) shield with at least 3 CT Clamp inputs and maybe a onewire temp and AC-AC measurement input.

The RaspberryPi could then host the emoncms, directly writing to a NFS share on a NAS many of us call their own anyway these days, either via Ethernet or an USB WLAN dongle (works very nicely on my rPI).

If someone is interested or has seen something similar or tried building this or any comments or possible obstacles and reasons not to do it please let me know.


pb66's picture

Re: Raspberry Pi Emon Shield

Hi Lightning and welcome to OEM,

I think a EmonTX shield for Raspberry Pi would be a great idea. It's something I've been thinking about for a while and would like to pursue it further. 

My initial thoughts were basically to copy the EmonTX designs minus the RFM and power regulation circuits onto a shield-like board that plugs directly onto the GPIO connector on the Raspberry Pi using a stackable header so I can still use the GPIO for other connections (or possibly the rfm2pi when I add remote nodes).

I was also considering using SPI rather than serial uart for data as this method can be used with multiple AVRs stacked if more inputs required and can also be used to upload sketches to the AVRs directly rather than using the external usb programmer.

So I am still very much at the idea's stage and as yet I haven't seen any posts specifically on this type of project either but I believe there are a lot more Raspberry Pi based systems out there now and I'm sure others have considered similar ideas :-)


Robert Wall's picture

Re: Raspberry Pi Emon Shield

If I can chip in with some encouragement - there have been several comments (I haven't been counting but I think it's in the half-dozen area) about using a direct connection, rather than radio, to the RPi in these forums so there is definitely some interest in such a design. 

joshpond's picture

Re: Raspberry Pi Emon Shield

There is a post of someone who has made a direct connection to the Rpi.

I can't post links it seems but search

Direct connection, original post was by Nubble and Chacal has the connection in the for sale thread.




bernamorillo's picture

Re: Raspberry Pi Emon Shield


I have been thinking on that a lot.

I believe it will be a wonderful alternative for small houses and some people can`t pay a lot for sensors. It was the main idea of OEM: Open this world to mainstream.

We are leading a European Efficiency Project:


And we are developing Arduino devices in our neighborhood to monitorize houses.

Nowadays we are spending 300€ per home because we don't have internet in the most.

We want to develop a local system in order to advise dwellers about how to save energy and money at home

Also we want to install the cheapest system as possible in order to change the mind about energy wasting.

I have been spoken with OEM staff and they don't think this idea could be so good. Here you are tweets between us:


We will develop some sensors nodes as CO2 plugged sensor and Solar Radiation wireless sensor. We are working on them nowadays.

We believe a cheaper alternative to OEM could be "Raspberry EOM shield" because you can offer less than 100$ systems. A really cheap OEM system costs 150€. Here you are the parts:


Finally I want to congratulate Glyn and Trystan because their work is amazing. I have been dreaming with this marvellous idea every day in my career as an Architect and finally there are a solid alternative to commercial systems. I didn't know anything about programming or hardware and I am learning day by day because of their work.

Thanks and keep ahead!!!


pb66's picture

Re: Raspberry Pi Emon Shield

So a bargain basement basic "shield" would be very easy to implement as the pair of RF boards would be replaced by using 1 reset and 2 serial pins, which would require only minimal changes to any existing EmonTX sketch and no change to the EmonCMS or Raspberry Pi software.But as there is no longer any rf and the serial port is now used there would be little scope for flexibility or expansion. This is the method used here ( http://openenergymonitor.org/emon/node/2327 ) but as this would be all 3volt the level converter wouldn't be needed. This is the simplest cheapest method to connect a single node directly.

What I believe would be a better solution is to have the ability to "just stack" the shields and the same communication lines are piggy-backed. I could be wrong but I believe the serial port is not suitable for this, so maybe I2C should be used to allow 2 directional comms between several devices ie raspberry pi as master and each AVR as a slave,

MartinR has used I2C to interconnect 3 EmonTXs ( http://openenergymonitor.org/emon/node/1170 ), of which one is a master and uses an RFM to connect to the base, this method like the serial port method only requires changes to the sketches but not to the RPi/EmonCMS software. To use I2C direct to the Pi would involve making changes to the gateway or an additional software interface. This is where I need a little help....well alotta help actually!

In addition to this set up it is also possible to use the Pi's 3 SPI pins to each AVR along with 1 pin per AVR (as an SS/reset) to set up an in circuit programmer to upload sketches to multiple AVRs direct from the PI over ssh. This eliminates the need to use the usb programmer and therefore can be done totally remotely with out any physical contact. This part I have had up and running on breadboard but further research leads me to believe that the SPI is less suitable and harder to implement than I2C for the normal comm lines, so a combination is the way forward I believe :-)

I hope I've made sense and would love some feedback on these thoughts. I am keen to sort the software side of things as then I can try some hardware configurations eg a basic simple low cost single phase board which can then be stacked three times to serve a 3phase install without any modifications or additions and/or then still be able to plug an rfm2pi in on top of them for further remote nodes as the serial port is still available.

Can I call upon the expertise of someone to assist or advise with the I2C, at both the avr and the pi ends? assuming my conclusions are correct of course :-)

Lightning's picture

Re: Raspberry Pi Emon Shield

Hi again,

as it looks like there is nothing available to date I've created a Raspberry Pi shield.




It features:

  • 3 x 3,5 mm Stereo plug connectors for 3 Phase current sensor input
  • a Barrel Jack for 9V AC-AC measurement input
  • A 2,5 mm Stereo plug connector for onewire sensor, highside powerswitched
  • A 2,5 mm Stereo plug connector for pulse counting sensors, highside powerswitched
  • all inputs are equipped with an additional TVS Diode (Just in case)
  • a dedicated area for a solder on RFM12B board (connected to the AVR's SPI bus) including a SMA connector for an external antenna
  • It's own LDO 3v3 regulator, the RPi's 3V3 bus only allows for max 50mA additional load which 'should' be sufficient, but not worth the risk
  • only SMT parts, smallest 0805 to allow for convenient hand assembly
  • an FTDI connector + ISP connector + ability to flash via bootloader from RPi (reset circuitry)
  • a PCP layout which should fit into a standard RS-Components RPi Case (764-4382)

Partnumbers and suppliers can be found in the part attributes for special devices.

The basic current measurement circuitry is taken from the EmonTx V3.2 schematic.

The Software would need some adoptions to feature both, a RFM12B gateway as well as local measurements, but lets cross that bridge when I get to it, the important feature for me currently is only the current sensing part, the other components are only added for more future options.

I've not yet built a prototype but maybe the community has some helpful comments or corrections to add, otherwise I'll build a first sample board within the next few weeks.



glyn.hudson's picture

Re: Raspberry Pi Emon Shield

Hi guys, just  found this thread. Great stuff.

I think there has been a miss understanding between myself and bernamorillo in our conversation on twitter. I was under the impression bernamorillo was asking if we had some sort of shield for the Pi available at the moment, which we don't. I suggested an emonTxShield and Arduino Yun combo which would perform the same task but it not nearly as powerful as the Pi (and costs more). I think a shield board for the Pi would be a great idea.

I  have already been thinking about developing a shield board for the beaglebone black since it's got a decent onboard ADC which the Pi does not. However it seems at the moment the Beagelbone's community is not as active as is for the raspberry pi. However having an AVR onboard the shield to perform the ADC conversion task would not add much cost. If we used the ATmega328 the firmware onboard could easily be updated directly from the Pi using the Arduino serial bootloader as we do on the RFM12Pi. 

I've started work on such a board combining the RFM12Pi with the emonTx shield. I think a footprint for an RFM12B / RFM68 / SRF / OKK would be useful as this would allow the board to receive data from other senor nodes around the house such as the emonTH and send RF control signals to boiler / relay / plug control modules

What's people experience with wifi adapters on the Pi? I've tried a couple with varying results, obviously using an adapter which can hold a solid connection and reconnect if connection is dropped would be important for monitoring applications. 


bernamorillo's picture

Re: Raspberry Pi Emon Shield

Glyn, you are the best, there were a miss understanding because I am so noob, but I believe in your knoledge and criteria.

I am using http://www.amazon.es/gp/product/B008B7PZU4/ref=oh_details_o00_s00_i00?ie... with great results.

We still speaking here about it because I am thinking is a good idea too.


michaeljquinn's picture

Re: Raspberry Pi Emon Shield

I am running my PV monitor off the pi - see here  amd its working fine - Can can send setup details no probs

Combining this with the EmonTx is a perfect solution for me, and then I can move onto building an OpenHAB based solution, which is my long term goal



michaeljquinn's picture

Re: Raspberry Pi Emon Shield

Hello all

How are we going with the raspberry pi shield for EmonTx V3 ??, really interested in using such a device, as it 

would be a perfect adjunct to my solar panel monitor.  I have run out of usb ports (1 for RS485 and another for WiFi).

Not sure whether another module would overpower the little pi though


keep up the great work



ukmoose's picture

Re: Raspberry Pi Emon Shield


If you look to the right, you should see a forum posting entitled "EmonPi early prototype - ideas"


bob teatow's picture

Re: Raspberry Pi Emon Shield

See also MK802 - it may actually be cheaper and easier to use an inexpensive Android-Mini-PC + your favorite Arduino with USB. ( http://openenergymonitor.org/emon/node/5570 )  You can wipe off the Android and run a another version of Linux.

Or if you really like the one board idea - pcDuino ( http://openenergymonitor.org/emon/node/5551 )

Or Arduino Tre - which is is a dual processor board - approximatelyan Arduino Mega + Raspberry ( http://arduino.cc/en/Main/ArduinoBoardTre )



Paul-_ece's picture

Re: Raspberry Pi Emon Shield

I'm a noobie here but joined because I would like to be able to monitor solar potential and demonstrate this at fetes around the Eastbourne area in the UK. Myself and a few others have started a community energy group with the idea of generating renewable energy and using any profit to reduce energy use through advice and help.

Having the ability to accurately monitor and display energy generation would be a very useful tool. I don't know if Michaeljquinn is still active but I would be very interested in understanding your setup


Robert Wall's picture

Re: Raspberry Pi Emon Shield

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