AVR-DB: emonTx V4, new hardware in progress

Thanks Brian, so assuming the new EmonTx v4 hardware is available to buy (hopefully not far away), what else do I need to get it running with a WT32-ETH01?

I can’t find too many details about the new v4 hardware, other than it supports 6 CT clamps. How would the ESP32 module link up to the EmonTX hardware?

I presume I would still need the EmonVs unit for accurate voltage sensing?

Just connects to 3.3V, gnd, TX, RX. I built a small add-on board to connect to the headers available (Trystan posted photos of his factory addon boards). To get it inside the case you’ll need a bit of case modification for the cable.

My ESPHome component is still in development, but it works :slight_smile: I’m just working out how best to enable folk to use it is they do not use HomeAssistant.

Yes and it will power the device as well.

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I will keep an eye on the store and hopefully will be able to get my hands on one soon.

Thanks Brian, very helpful feedback.

There’s an ethernet equipped Pi Pico (W5500-EVB-Pico) but I don’t know if it’s compatible with the proposed Pico interface board or if it would fit in the enclosure.

That is quite neat (W5500-EVB-Pico) but there is insufficient height to fit inside the enclosure as things stand. It would need an add-on board such that the Ethernet board could be fitted upside down.

If someone had the wherewithal to create a 3D Printed enclosure for the TX4, it would make this feasible.


Hello all, we are happy to say that the EmonTx4 is now available in the shop :tada: we will be able to ship the first set of orders early next week.

We are starting with a quiet launch as we continue to gear up with this new product. For those of you who have been following along here for a while, we would like to say thank you with a 10% early bird discount code O3N5S93TFQ (Available until next Monday 28th of November).

Items in progress

  • We are in the process of moving from the old guide documentation to a new site based on ‘Read the docs’. Please see: https://docs.openenergymonitor.org/emontx4/overview.html
    This will house both the existing documentation e.g emonPi and emonTx v3 in addition to the new hardware. This new implementation builds directly from the documentation placed in e.g the emonTx4 GitHub repository itself, so you can choose to either view the same documentation on github or with the nice ‘Read the docs’ theme.

  • There’s more to add to the EmonTx4 documentation section as well, including using the EmonTx4 with an integrated WiFi extension board, a heat pump monitoring focused install guide discussing how to use the broken out analog input to interface with a voltage output Sika flow meter. Details on the temperature sensing and RFM69 radio among other items.

  • New emonSD image release, we will do a separate announcement about this over the next few days.

  • EmonTx4 Pi Pico, Pi Zero, ESP8266 and ESP32 extension boards will be available as bare PCB development boards in the shop (Shop items still to be created) - these are only for those happy with a bit of soldering and code uploading for the time being.

  • We also need to create the shop item for the lower cost emonVs mini (voltage sensor only - no integrated power supply) and the ACAC adapter converter board.

  • This first release is the single-phase 6 channel configuration, the 3-phase version will follow later. If you do want to order an emonVs voltage sensor with the hardware capability for 3-phase so that it can be used when the 3-phase firmware is available, please email us and we can arrange that: [email protected].

We would welcome suggestions or pull requests for changes to the documentation. The emonTx4 documentation files can be found on github here: emontx4/docs at main · openenergymonitor/emontx4 · GitHub

Let us know if you have any questions regarding the bundle options selection.

@glyn.hudson has also just updated the theme on the shop to something a little more modern :slight_smile:

Thanks everyone!


@TrystanLea - That’s fantastic news! Well done you guys.

Am I right in thinking that we can add Wi-Fi at this stage but it requires soldering on the module?

Thanks @abbbbbottttt out of the box only when used with the emonBase (raspberry pi Wi-Fi) at the moment.

We will also be making the EmonTx4 Pi Pico, Pi Zero, ESP8266 and ESP32 extension boards available as bare PCB development boards for those happy with a bit of soldering and code uploading, is that what you are after? Here are the links to the brief documentation pages for these so far:

The Pi Pico option is looking like the direction we are most likely to be going at this point, in terms of focusing our efforts longer term, for the non full Pi application that is.

@borpin has also been doing some good work on an ESPHome integration currently tested on an ESP8266 though possibly soon also available to run on a Pi Pico by the sound of things!


This is great news, I am happy to jump in and be an early adopter!

Question on power though, I don’t really want to buy the expensive PSU if I can re-use one of my 3 existing ac/ac bricks. On a mobile device so hard to scroll through the detail but was there an adapter board for voltage, is that available yet?


Hello Trystan,
just want to double check: the 3-phase version is just a firmware change, i.e. not different hardware? So if I want one 3-phase unit and one single phase I can just order two now and do a firmware update later. Is this straightforward with a PC ? I would like to order both if possible because I am in Germany would save on postage.

Do I need a 3-phase device if its only being used on a AEG 3-phase oven-grill, i.e. no motors ? The device can use a bit of power but I don’t know how it balances load.

Very pleased you guys got this pulled together!



I think there will be an adapter cable for the round 9V to the RJ45 socket.

thanks @borpin yes that’s correct, coming soon!

Ah found it, so I think what I need is the single phase precision option - I’m in so deep at this stage it probably makes sense to go for the more accurate reading.

The RJ11 just looks like a physical adapter, are there components on that board, or could something be made up as an interim solution?

Does the EmonPi benefit from the accurate voltage reading, or is it only of benefit on the circuits monitored by the EmonTx4? Wondering if I put the solar into a channel on the EmonTx4 and move it off the EmonPi if so.

Thanks Marc!

There is a hardware difference but we can send you the version that will be ready for 3-phase monitoring. I will double check with @glyn.hudson how we can administer that in terms of the shop, the cost for the 3-phase version is about 10% more than the single phase version (It includes two additional ZMPT precision voltage transformers).

Yes, if you have an emonBase or existing emonPi it’s easy to do this by connecting the emonTx via USB, see the example here for upgrading the current firmware: https://openenergymonitor.org/guide/emontx4/firmware.html#updating-firmware-using-an-emonbase.

I cant say, my guess would be that it might put the oven, grill and hobs on different phases? Are the other circuits in your house all on one of the 3 phases?

Great, yes we’ve already prepared quite a few of these, just need to get the shop item up, which we will likely do tomorrow. When using the single phase voltage sensor only, the emonTx4 does require a separate USB power supply. Will the emonTx4 be located next to your existing emonPi? if it is you could power the emonTx4 from the emonPi, you could also transfer the measurement data to the emonPi over the same connection.

The emonPi cant benefit unfortunately from the emonTx4 voltage sensor.

Yes the EmonPi is already next to the CU, so I plan to hard wire the emontx4 with usb to the EmonPi for power, data and the ability to flash FW.

Sounds like I need to be patient another day or so :smile:

I need to do some head scratching on what circuits get the honour of measurement and what CT to order, I have to get the immersion on one but then I have 3 rings, want to track the oven and then there is lighting.

Will need to compromise in some way before the expansion board is available… then I can really lecture the family with graphs on their energy usage!

I think the only way it could present a balanced load would be it works by induction and all the elements were controlled electronically - power being derived from all three phases to feed a d.c. bus, or something like that.

If not, I think it’s a near certainty that individual heating elements will be arranged to spread the load across the three phases, rather than balance the load. but exactly which it does Marc would have to find by experiment or consult the manufacturer.

I’ve added a hidden shop option for emonVS 3-phase:

Can I just clarify that this can be used with an existing emonPi, and if so how? The documentation and the shop talk about an emonBase, but doesn’t appear to explicitly say it can be used with an emonPi. Is the connection over wifi?


In fact I’m a bit confused what I need now.
I have an emonPi which is doing some ct sensing and some temperature sensing for my heat pump.
I need to expand that to include some further ct sensing elsewhere (immersion heater), some temperature sensing (hot water tank), but mainly modbus reading of a heat flow meter. I’m unclear what I need. There are three separate locations involved (maybe 2, depending on how what kind of wiring you need for the modbus). I can’t get a wire from the flow meter to the existing emonPi, though I could probably replace the emonPi with an emonTx and relocate the emonPi to where I can get a modbus wire connector.

So either way it looks like I need an emonTx, what I’m unclear about is whether I need an emonBase as well, or indeed anything else, and whether my existing emonPi stays, or gets replaced.

Thanks (sorry for the confusion).