emonPi2 Pictures & Spec

We are nearing the release of the emonPi2! It should be available by December 14th, provided everything goes according to plan. We are currently awaiting the production of the laser-cut enclosure panels. We are very pleased with how the enclosure design has turned out, thanks to screentec.co.uk.

I’ve been preparing the product pictures for this today and creating the shop entries :grin:

Product pictures:

(Incorrect capitalisation of MHz will be fixed in the production version :face_with_peeking_eye:)

emonPi2 features:

Measurement board:

  • 6x clip-on CT current sensor inputs (suitable for a range of 333mV voltage output CT sensors)
  • Voltage input for use with emonVs precision voltage sensor (RJ45 connector)
  • Full Real/Active power measurement & continuous sampling
  • Cumulative energy persisted on reboot
  • Optional pulse counting and analogue voltage input
  • On-board USB-C to UART converter for easier programming and serial output
  • Handled by the Pi: DS18B20 temperature sensing* (pluggable terminal blocks required)
  • Handled by the Pi: 433 MHz RFM69CW radio transceiver

* See discussion here about the number of sensors that can be connected at any one time to a single raspberrypi one-wire bus. We have tested 6 sensors with no issue.

Integrated base-station:

  • Raspberry Pi mini computer
  • Full local data logging and visualisation capability using emoncms.
  • Option to post data to a remote server such as emoncms.org
  • Data accessible via MQTT
  • Software support for reading from Modbus & M-BUS meters via USB
    (Please select RaspberryPi 4 for externally accessible USB ports)

The emonPi2 builds directly on the development work behind the EmonTx4. The schematic is almost identical, it has the same AVR-DB core, CT input and voltage sensing circuitry, the firmware is almost identical. The main difference is that when used in conjunction with a RaspberryPi, the temperature sensing and the RFM69 radio is handled by the RaspberryPi (which leaves the main microcontroller to focus on electricity monitoring). It also has an OLED display to help with setup, in particular finding it’s IP-Address, much like the original emonPi v1.

The board is designed in such a way that it can actually be used as an energy monitoring transmitter (effectively an emonTx4) if the RaspberryPi is not connected. The AVR-DB core can take over control of the RFM69 radio module to transmit data to a listening base-station elsewhere.

Il post up here more specific technical details over the next set of posts, what the differences in the firmwares are vs the emonTx4, schematic and board references, internal build pictures etc.


Looks great. Integrating the PiZero2 is brilliant and keeps the cost down nicely.

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Thanks @borpin, agreed the PiZero2 is a really nice option to add and thanks as ever for the recommendation!

Although the CT expansion board which will provide an additional 6 CT sensor inputs will not be ready at launch, it will be an option that can be added to the emonPi2 as well and fits together with the Pi Zero in the same enclosure (but not the Pi4).


Even more reason to use the Zero :slight_smile:

Your order number is 32170



Thanks David! you are the first customer!! :slight_smile:


Do I get a free yacht?


More pictures!

Top of the measurement board PCB

Bottom of the measurement board PCB

Top view with LCD connected


Pi Zero 2W build pics coming next, and partial enclosure build pics :slight_smile:

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:rofl: If we were a boiler manufacturer you’d get a trip to somewhere exotic to undo all the carbon savings :wink:


I’ve adjusted the text here to be less hyperbolic. I’ve tested up to 6 DS18B20 temperature sensors at any one time. There’s a useful discussion here about others more general experience of the number of DS18B20 temperature sensors that can be connected to a RaspberryPi digital input that may be useful. The OpenEnergyMonitor documentation also covers some of the intricacies around cable lengths etc when using DS18B20 temperature sensors here Temperature Sensing Using DS18B20 Digital Sensors — OpenEnergyMonitor 0.0.1 documentation

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Enclosure side open

Enclosure top open

Mounting of RaspberryPi Zero 2W


Looks really great.

Couple of suggestions for shop page;

  1. Add the cost of the option in brackets (e.g. different emonVs)
  2. change the CT selectors to dropdowns (so more compact - when you have the option of 12…). Alternatively, a choice of number of each type of CT like the temperature sensors (would need user to configure then of course) which then could have a price next to it.

One other note - at the bottom of the emonPi2 page, the Wi-Fi version of the TX4 is listed. This isn’t listed on the Electricity Monitoring - Shop | OpenEnergyMonitor page :frowning:

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If I am ordering for the US, and I want EMONVS, what plug do I select, the “no plug, single phase emonVS” option?

You do want “No plug”, and you’ll need to wire it to a suitable plug, or you can of course (and probably better and more reliable) make a permanent connection, but I understand you’ll need a registered electrician for this. Do you want to monitor the voltage on both legs of your split-phase supply? If so, contact ‘The Shop’ and ask, because you’ll want a special ‘two-input’ version, alternatively the 3-phase version with only two inputs used.

See also emonTx V4, emonVS in North America

Just a (unfortunately rather late!) thought - could something like a Panel Mount Extension Cable (50cm) – USB micro-B to A (e.g. Pimoroni CAB0902) be fitted between the RaspberryPi Zero 2W USB port and the Raspberry Pi 4 connector knock-out panel?

Would this allow the Zero 2W emonPi 2 to be used to update the firmware on other emon units? …

Also to allow a wired connection between say an emonTx4 and the emonPi 2? …

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@TrystanLea this looks like a very nice addition to the line up. My EmonPi is currently run of an EmonVS usb connection and uses the traditional block for the voltage source. The EmonVS rj11 runs an EmonTx4. Would the emon Pi2 (Pi4) be able to piggyback off the EmonVS voltage connection to get a voltage, or would it try and draw power too?

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This is a good idea, but probably a mico to micro would be better although quite a lot of cable to ‘lose’ (Panel Mount Extension USB Cable - Micro-USB Male to Female | The Pi Hut).

Personally, I’d notch the end panel and just put an OTG cable through that, plus a short HDMI cable too (that would be useful for the usual Pi as well :slight_smile:

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I chose a USB-A female connector to go on the knock-out panel to give external access, because:

a) It would be the same USB connector as that used on the emonPi2 Pi 4B version and the original emonPi.

b) If you want a direct cable connection to an emonTx4, you would need a USB-A male to USB-C male cable, which are fairly common.

c) If you want to update/serial connect to an emonTx3, or update an emonTH, you would need a USB to serial TTL adapter. My USB to serial TTL adapters all have USB-micro female connectors on them. I have plenty of USB-A male to USB-micro male cables (from old phones), but no USB-micro male to USB-micro male cables.

d) Most (all?) of my separate USB to USB cables (apart from Pi Zero USB adapter cables!), have a USB-A male connector on one end. I’m not sure about the availability of a USB micro male to USB-C male cable, or a USB micro male to USB-micro male cable.

For a diy modification, then the connector used would obviously be a personal choice! :blush:

Always assuming that I haven’t missed something in the basic idea of connecting to the Pi Zero 2W USB connector!