EmonTx4 Documentation

@TrystanLea I think this extended info on the DS18B20 sensors would be worth condensing for posterity. It is really useful and probably also worth mentioning in the docs that ‘cheap’ sensors can cause issues (I think it came up recently again IRRC). Ds18b20 and emonTX3CM firmware - #78 by dBC #pleaseaddtothedocs

I did find that slightly confusing. I have 3 temp sensors to add for my hot water system, I read the paragraph:

However it is worth noting that due to the way that the one wire protocol works, specifically it’s requirement for precise timing requiring brief periods of disabling other interrupts on the microcontroller, that there is a minor negative impact on energy monitoring performance as you add more temperature sensors. This can manifest as a ±1-4W error on some CT channels. This effect can be mitigated to some extent by reducing the electricity monitoring sample rate.

So does this apply to the 3 separate inputs, the RJ45, all of them, is there a priority to follow? Should the EmonPi be used first if available to preserve accuracy on the EmonTX4 where possible etc?

Also the lack of connector for two of the inputs is an oversight in the shop listing IMHO

Yes it applies to all DS18B20 temperature sensing, regardless of input - they are all on the same bus/digital input pin anyway.

If you have the standard emonPi firmware rather than the newer continuous monitoring firmware for the emonPi then yes that may be worthwhile - that said the effect is very small. If the emonPi is running continuous sampling firmware the same mechanism is present. Though it may not be visible due to a slower sample rate. Im hoping to do some more work on this soon (with Roberts input).

Our thinking here was that most users will be using the emonTx4 for electricity monitoring only. That’s seems to be consistent with most orders to date. The pluggable terminal component is also not that cheap, adding 3x of them is more than the cost of the main microcontroller! We thought that rather than add this cost for all users we would instead include them with the DS18B20 temperature sensor shop item.

Discussing with @glyn.hudson we think that the best option is if we create a new shop item specifically for these pluggable terminal blocks so that users who already have DS18B20 temperature sensors can add these as required. We will add a clear note to the emonTx4 description to point to this shop item. Adding them as an option on the emonTx4 page is more complicated as there is potential for confusion when ordering the DS18B20 temperature sensor options (which already include the plugs).

Thanks, I will wire to EmonPi then as I am still on the original discreet code at the moment, I also plan to use the breakout board (purchased many years ago!) to run one ethernet from the airing cupboard to the EmonPi/EmonTX4 near the CU and run a few temp sensors which I have again purchased from the shop over the years.

The plugs - are you using Camden Boss fancy ones or multi comp ones? I assume the plugs are something like this 3.5mm spaced?
CPC 3 way 3.5mm plug

Appreciate the difficulty in adding the options to the EmonTX4 page, but perhaps a note 1 is included, or none if it makes more cost sense, and they need to be bought as needed?

I can see how they are better than taking apart the case to access screw terminals, which in turn may mean removing something from the wall etc etc

I havent updated on this documentation thread for a while. I am working on a couple of fairly large updates to the documentation: a page on using the emonTx4 for heat pump monitoring and updated emoncms documentation, it is taking me a little while longer than I hoped but it is on the way :slight_smile:

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From recent questions - suggested additions;


  • Include details re updating firmware
    • UART to USB (TX/RX)
    • DS v CM firmware
  • Connecting via serial to a Pi based device either as a USB or a GPIO connection. Which emonhub interfacer to use.

This for serial connecting to GPIO pins.

Various bits in this thread including building firmware on the Pi and uploading it directly. This was my final setup

Thank you @borpin that’s really useful.

I’ve uploaded a couple more guides:

  • emonTx4 heat pump monitor guide - this is a work in progress. There are parts I need to extend in more detail especially around the flow sensor ecodan controller connections. I also wonder if moving the longer discussion of temperature sensor mounting and error to learn might be a better place for it given that it’s transferable to other hardware.

  • emonCMS emonPi/base getting started guide

  • emonTx4 & emonVs voltage sensing technical description - to be extended with details on adjusting calibration when attaching multiple emonTx4 units to a single emonVs output and also more detail on LTSpice simulation parameters for the ZMPT101B.

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I think there may be a small spelling error on this page.

Note: by default the new version of the emonBase with the RFMSPI is NOT compatible with **order** hardware e.g emonTx V3 and emonTH V2. Please contact us if you would like a version which is compatible with older hardware. 

I think that order should be older.


Thanks @alc_aardvark fixed!

I’ve updated the documentation with some of your earlier feedback @borpin

All amended/improved.

fixed this, thanks

added a note on this, thanks.

The USB-C connector orientation images are also added in now.

I’ve also modified emoncms to first fetch the available firmware list from the github repository which should after one more system update not then require further system updates just to make the latest firmware available in the firmware update list.

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@borpin not covered everything you’ve mentioned re emonTx3 firmware yet, but here’s a start: Firmware — OpenEnergyMonitor 0.0.1 documentation

I’ve also copied more of the wiki page content over onto the technical page: emonTx Technical Overview — OpenEnergyMonitor 0.0.1 documentation more work to do on that as well.

Great @TrystanLea. Have you found how to point the docs page back to the source file yet?

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Yes finally worked out a solution for the edit source links, so far applied this to the emonTx4 pages. Need to extend to the rest of the documentation.

I’ve also moved the github repository for the documentation to: https://github.com/openenergymonitor/docs

and improved the way the separate emonTx4, emonTx3, emoncms etc repositories are linked into that to make it much easier to install and update. Im back to using git submodules but structuring the directory differently.

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But is it going to be easy for users to find what they’re looking for? This is the most important part.

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This is just the structure of the back end source, not the display.

So far it looks much better, easier to search etc. Yes there could be issues, but easier to fix as the source to content part is simpler I think.

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Is the guide for extending emontx3 CTs still valid for the voltage based emontx4 CTs? If so, perhaps include a link to Learn | OpenEnergyMonitor in the emontx4 docs?

Yes, no change to front end display structure in yesterdays update.

Yes the CT extension guide is still valid. I will link that in, thanks @menocar

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2 posts were split to a new topic: Sample interval for TX4 and missing RF data

Pulse Counting

I have posted the direct to Pi config for pulse counting (again I think) ASHP compensation curve, UFH and wood burner - #11 by borpin

I have found an earlier version here :slight_smile: emonHub Interfacers — OpenEnergyMonitor 0.0.1 documentation Could this be updated with this better info.

Generally, searching for ‘Pulse Counting’ in the docs shows up some anomalies in the docs (no criticism - partly due to migration).

The heading Pulse Counting appears in the results 3 times, but it is unclear the context (Emoncms, emonpi and emonTX). Not sure how this could be solved! I note some results have the page name → topic. Perhaps some of these pages actually need to be combined so the context is clearer.

Overall, I did eventually find what I was after, but it took some digging and I think this could/should be easier.

Do we need summary or aggregation pages. So a ‘Pulse Counting’ page under a sensors heading perhaps that links to - Direct serial, EmonTX3/4, EmponPi, Emoncms? MIght that help to bring subject areas together?

I was having a look on the pulse counting Docs page at
and it is shorter and rather different from the original Guide page at

In particular I was looking for the 12 input pulse sensor, but these links in the original pulse counting Guide page (in the Learn section just above the appendix)

don’t seem to have equivalent content in the Docs pages. The links direct me to the Docs pages, but there is no relevant content in the Docs/Pulse counting section… Are these topics still available somewhere?

Also these two links at the bottom of the Docs page don’t seem to work for me

One other point - when you have finished reading something in the docs pages, how do you get back to the OEM home page, apart from editing the URL in the browser - or am I missing something?

I understand that the Docs section is a work in progress, so I apologise if I’m putting the cart before the horse!