AVR-DB: emonTx V4, new hardware in progress

Postman finally turned up with my EmonTX4 yesterday (it shipped last Friday, ironically an IP camera I was waiting for shipped from Hong Kong Monday and arrived first - Royal Mail living up to its reputation!).

First impression was it was a large cable in a box with some other stuff :rofl: as others have commented the cable is huge, mine was 2m not 1m - I assume the moulded plug is for regs?

I would consider looking at IEC leads, they are cheap and plentiful and you can just chop the IEC and wire it in? I need to change the lead somehow as this one is massive and I have no where to hide it in the WC where the builder helpfully installed our CU. I’ll have to look at adding a fused plate maybe and wiring it into that directly to neaten it all up - low WAF as shipped (Wife Acceptance Factor).

I will update my EmonPi first, I am on 11.0.9, reading the release notes can’t see much change to 11.2.3 but might as well be current.

My EmonTX are all CM FW now, can the EmonPi run continuous monitoring by default, or is it still for experimenting only? At the moment my solar is on the EmonPi so any increase in accuracy is welcome.

-5c here in the south of England this morning, but the sun is out and the skies are clear so off the grid at least!

In case it helps anyone, it looks like EmonTX4 is Node17, its confusing as I already had an EmonTX4 which seems to be my 2nd EmonTX3 with Node ID 16.

I clearly need to do more reading as I am not sure if you can rename nodes already in use? As long as the feeds are not touched it seems you can delete and add nodes and inputs freely?

Is there any news on the 6 CT Expansion Board yet ?
Also will it fit into the existing case ?

Hello @Tank, the firmware to support 12 CT sensors is almost ready, going through testing at the moment. I cant say exactly when it will be available in the shop yet. The Expansion board itself does fit in the existing case, it just needs a different fascia. Are you interested to add this to an emonTx4 that you have already or is this a new system?

Thanks @TrystanLea , It’s to add to my existing Tx4.
That’s good to hear that it will fit in the existing case as well…

The 3 phase compatible firmware library called emonLibDB and associated firmware examples has now been released, thanks to @Robert.Wall. We are looking for folk happy to test and give feedback on the process of using the firmware.

Please see the forum thread here for more information, it also links to the original emonLibDB library release that makes this functionality possible:

EmonTx4 3-phase support with emonLibDB

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The 6 CT Expansion board is now available in the shop

and the installation and firmware guide can be found in the docs here:
6 CT Expansion board — OpenEnergyMonitor 0.0.1 documentation

The expansion board is currently listed in the development boards section of the shop as it’s really for those comfortable with soldering the header and manually configuring, compiling and uploading the firmware using the Arduino IDE. We can do these steps for you if required when ordering the expansion board alongside an EmonTx4 in the same order, please email us first at [email protected] to discuss how you would like us to configure the unit.

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We are also gearing up here for the emonPi2 release! Probably around a month away.

The emonPi2 shares a mostly identical PCB design to the emonTx4. The only difference is the layout of the board, RaspberryPi GPIO header, OLED display connector and RJ45 rather than RJ11 emonVs connector for more power carrying capability needed for the RaspberryPi. This allows for a single enclosure design that integrates the RaspberryPi base station.


  • 6x clip-on CT current sensor inputs (suitable for a range of 333mV voltage output CT sensors).
  • emonVs precision voltage sensor and power supply input
  • Full Real/Active power measurement & continuous sampling.
  • Both single and 3 phase support.
  • 2 pluggable terminal block inputs for DS18B20 temperature sensing & pulse counting connected directly to the RaspberryPi GPIO header.
  • 1 pluggable terminal block analogue voltage input.
  • On-board USB to UART converter for easier programming and serial output.
  • 433 MHz RFM69 radio transceiver
  • Standard RaspberryPi GPIO header connection for direct connection to a RaspberryPi
  • Wall-mount aluminium enclosure
  • OLED 128x64 Display
  • Microcontroller: Microchip AVR128DB48
  • Arduino core support DxCore by SpenceKonde
  • ADC Resolution: 12-bit
  • Precision voltage reference: MCP1502
  • 6 CT Expansion board option as above to increase number of CT inputs to 12. Though only when used with the Pi Zero rather than full Pi 3/4 due to enclosure space constraints.

I’ve added an overview page to the documentation and will be adding to this over the coming weeks in preparation for the release:



With regard to the 6 CT expansion board, Do you plan to make a firmware available pre compiled that will connect via USB, as the documentation seems to only show source with RF included. Please correct me if I am wrong (quite possible).

Hello @Tank there is a firmware example here that prints out in the standard format via serial https://github.com/openenergymonitor/emontx4/tree/main/firmware/EmonTx4_DB_12CT_WiFi
It prints all power values but not energy values as it was customised for use with the EmonESP WiFi boards and I wasnt 100% sure on stability if the string length doubled again.

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Looking forward to Emonpi2… I am ready for a hardware refresh…

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Probably a little late in the design cycle,… but has any consideration been given to some forced cooling,.My ‘emonpi v1’ can get a little warm,… particularly when the ambient temperature reaches 40C… …although chips may be running within their rated temperature spec,… its always nice for their extended life to run them as cool as possible,…

Thanks @garyjuergens

@diyhouse no forced cooling, it’s not something we’ve looked at yet. Really the Pi4 is way over powered for what we need. It would be good to look at under-clocking, and other options to reduce power consumption / chip temperatures. Would prefer Pi3’s and the pi zero 2w, the latter we plan on making available as one of the options with the emonpi2.

The emonPi2 is now available to order:

See also new emonPi2 thread here: emonPi2 Pictures & Spec

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@TrystanLea , I have eventually got round to trying the 12 channel firmware, following the documentation on the wiki, but the sketch never returns any readings over the serial connection. If I add an “else” to print something at the end of the “if (EmonLibDB_Ready())” condition it is running, so it seems not to be returning “true”.
I have tried modifying a couple of other sketches as well and all work fine with just 6 channels, but adding the full 12 has the same effect. This is with the CM library so “if (EmonLibCM_Ready())” has the same problem.
Is there any plan to release an “official” firmware that is programmable from the EmonPi ?
If you wish to see my modified sketch, let me know.

I suggest you download the emonLibDB library zip package from this forum EmonLibDB - Version 1.0.2 and therein you’ll find working demonstration sketches for up to 3 current and 3 voltage channels (i.e. single phase, split phase or three phase but no temperatures), which are briefly described in the accompanying documentation.

You’ll need to add “trimmings” as necessary - i.e. I’m waiting for Trystan to specify what he wants by way of on-line calibration, then I can produce a “fully engineered” sketch which will fulfil your requirement of “programmable from the EmonPi”.

@Robert.Wall , Yes done that already with no success. The EmonTx4DB_rf sketch with the expansion board in compiles and uploads but then just sits there with
“EmonTx4 + EmonLibDB Continuous Monitoring Minimal Demo with rf
Starting reports every 9.80 seconds approx.”
on the screen.
Comment out the “#define EXPANSION_BOARD” line and the same happens.
The other two sketches for 6 channel only in the zip do the same.
I did re-download the zip and start again.
I have one sketch modified by me that I can switch between 6 and 12 channels, and when it is 6 it works fine, but not 12.

Have you got a voltage source connected?

@Robert.Wall , No not at the moment. I was programming on my desktop, but my voltage source is in use on my other TX4 in my “cupboard”.

That could well explain it. If it can’t count zero crossings, it can’t work out when to report. Put your finger on the bottom of the power connector socket (where the ribbon cable from the emonVs plugs in) so that it gets a bit of voltage pick-up from your body. It might get enough to run.

Because the concept all the time was an integrated power source and voltage reference - the emonVs - emonLibDB was never intended to run without a mains voltage to measure and derive its timing from.