Wired / Ethernet Sensor nodes with at least 6 (CT) energy consumption sensor + Home Assistant support


I have already home assistant server, currently in Raspberry Pi 3B PLUS.
I want to measure current consumption (summary / daily / current) in my home:

  1. ALL, it can be in highest load about 60A / 230V total because of multiple air conditioner / freezers / ovens / and more.
    And parts of this:
  2. Servers, PCs, smart home energy consumption with UPS
  3. Lights and Sockets
  4. Air conditioner
  5. Kitchen
  6. boilers (hot water)

I know, maybe it’s not important but it is my plan to watch this values.
All of devices have in same place the power input, so I will install all of consumption measurement to same place, so no need WIFI or other wireless connection.

What is your recommended solution to measure with at least 6 CT this values?

I also found some topics:

Simplified emonTx Arduino Shield + Ethernet Shield - Guide

BUT sadly I have no perfect skills about soldering, but I can if no other way. I don’t think I’m a first who searching solution to measure 6-8 node with wired connection.

I collecting my possible plans, what is all not perfect:

2 pcs emonTx V3 + 1x high single-phase CT + 3x single phase CT = 2 * (1+3) = 8 measure, its OK.
And I connect this 2x emonTx V3 with WIFI to my Raspberry Pi 3B PLUS and reading data with Home Assistant, it can works? BUT I don’t want use WIFI or wireless connection.
QUESTION 1: Any (easy) or already done solution to connect this 2x emonTx with ethernet (RJ45) to my Raspberry Pi?
QUESTION 2: This way can communicate with Home Assistant? Or you recommend to run on my Raspberry Pi EMONCMS and Home Assistant will communicate / read from EMONCMS?


I found here more details:
“EmonTX - Serial - Pi - EmonHub - HTTP API or MQTT - Emoncms Server (not necessarily on local Pi).”

So possible to connect with Serial, wired connection to my Raspberry Pi and that’s all?


3 pcs emonPi? For measure 6 node? Or 4x emonPi for meausre 8? It’s expensive, and nice scalable architecture.
QUESTION 3: It will works, and can I read all of 6 or 8 CT sensor’s data using Ethernet?
QUESTION 4: Any way to use only 1 emonPi and connecting 1x or 2x emonTx to this for process 2+4 or 2+4+4 energy measure? Only possible connect in wireless? Or possible to connect with etheret (RJ45)?


2 pcs emonTx V3 + ethernet shield = my Raspberry Pi with installed EmonCMS + Home Assistant process data and all done, because only wired, ethernet connection?
QUESTION 5: Possible to use emonTx with any Ethernet shield?

More simple solution?
QUESTION 6: Any already done solution to do this, with less developing, less DIY? What only use Ethernet and do the same measurements with 6 or 8 CT node?

UPDATE: After very nice comments I changed topic from “Cheapest Ethernet Sensor node with at least 6 (CT) energy consumption sensor + Home Assistant” to current one. Seems like wired connection is surprisingly more expensive, but it’s ok. 6-8 sensor will be nice. After I found the solution with strong help I will try to share my plan, hardware and software solution. I try to solder and develop less and using more complete modules, solutions if possible… in our DIY World… :slight_smile:

Thank you guys.

cheapest network and easiest method is buy two emontx shields and two wemos d3 and follow this. you have space for 8 cts but it is wifi and not ethernet – but natively works with home assistant, emoncms, and other home automation software

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Sounds like it’d work for him, except…

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You could move to the emonTx Shield and an Ethernet-equipped Arduino, or a plain Arduino with both Ethernet Shield and emonTx Shield. I’m not an Arduino expert, the Shield and its software are designed for the Arduino Uno, so I’d imagine that most Arduinos that have Ethernet and are Uno-compatible will be usable - but note the warning in the Wiki about compatibility. If you’re using an Ethernet Shield, bear in mind the emonTx Shield only stacks as the top one. And make sure you solder the connectors on the correct side of the p.c.b.

Or, have you seen this: Simplified emonTx Arduino Shield + Ethernet Shield - Guide

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Thank you for answer.

So, I get:
2x emonTx Arduino Shield SMT with No RF.
2x UNO+WiFi R3 ATmega328P+ESP8266 Module 32Mb Memory USB-TTL CH340G.
Soldering, software, firmware changes and I will connect this emonTx with UNO.

And I need connect with WIFI. Thank you, this is my first PLAN now, what can work. If I find no other without WIFI, I will choose this.

Thank you again to helping me. It also can be more expensive is using Ethernet not WIFI.

I will put all of measure devices to same place, like 1x1 meter in wall and also the Home Assistant, router, switch also in this area inside. I have many negative experience about WIFI STOP working, packet loss, etc. For this usage I see no point to use wireless communication. Maybe if I have 2 or more power source, no question, wireless communication good idea. Or if my Home Assistant server far from power measure place, etc…

Thank you for share this solution. I’m never used any Arduino, only Raspberry Pi for few projects. Can you or anyone recommend me exact hardware what will works together and need LESS soldering, changes for work? Like already soldered or made in one officially Arduino + Ethernet connection what is compatible with emonTx.

Hey! :slight_smile: Not possible to connect in any proper wired way easily any Arduino to Raspberry Pi? This can be a solution? Like serial or usb connection? I no need extra communication layer if not necessary, I just finding a wired, stable solution for 6-8 CT sensor. What do you think, a Raspberry Pi 3B PLUS enough strong to read / process emonCMS? And with Home Assistant too? Or Raspberry Pi 4B 4GB recommended?

No one in the World want to use this Open Energy Monitor with wired connection + 6 or 8 sensor? So strange for me to not have yet any out of box product or easy kit for that. Please make 1 for me yay! :slight_smile: I can wait 2 months for that product! :slight_smile: Just I getting components (2-3-4 nodes, 1 main controller device optional and 6-8 CT sensors + cables, etc), connecting devices/modules, software setup and done!

I think the simplest solution would be 2 emonTx’s connected to a Pi, one via the GPIO serial port (aka serial-direct) and the other via a serial to usb adapter (aka usb programmer).

The emonTx’s already output via serial (for use with emonesp) and using usb and GPIO means there would be no confusion between device addresses as one would be /dev/serial0 and the other /dev/ttyUSB0, therefore no editing the sketches to write a node I’d would be needed.

No soldering, no programming, just use the emonSD image and make some settings changes to emonhub.conf and you’e all done.

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I was trying to tell Stephen you don’t want to use WiFi.
I agree with you about WiFi. I’ve not had the best of luck with it either.
Like you, I prefer Ethernet over WiFi.

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Hi Stephen, I now getting closer the solution! :slight_smile: Thank you!

I get 2x emonTx,

  1. emonTx will connecting with serial to Raspberry Pi, details here. It’s correct info and manual to do this?

  2. emonTx will connecting with USB to Raspberry Pi. I not yet found instructions how to connect emonTx to Raspberry Pi’s USB? Can you link me any hardware parts / cables or what else needed to do this?

Also possible to connect 2-3 emonTx with serial or 2-3 emonTx with USB? What is a limitations?

Anyone have any specs / experience about sensor reading speed limitations in different data bus, like serial or usb? And connection limits? Like how many possible in same bus what is still usable and works fine?

hi the emon tx they are referring too in the document is this one it different then the emontx shield – you could still do it will the shield but you still need either 2 basic uno or the the above mentioned wemos D3 - and firmware that imitates the emontx serial output- I am sorry i can not help you there as i am not so familiar to emontx serial output format

and for usb serial
instead of this in the above mention config you provided

    type = EmonHubSerialInterfacer
      com_port = /dev/ttyAMA0
      com_baud = 9600

it be more likely this and you would just use a normal usb cable an connected to the uno/wemosd3

    type = EmonHubSerialInterfacer
      com_port = /dev/ttyUSB0  
      com_baud = 9600

but also here i am not so familiar as i have not work very much emon software

the only problem with multiple usb serial are them switching at boot
device1 = /dev/ttyUSB0 device2 = /dev/ttyUSB1
at the next boot
device1 = /dev/ttyUSB1 device2 = /dev/ttyUSB0
you just have to make them static - but I never tried but here a how to how to

but instead of com_port = /dev/ttyUSB0 you would use the name that you gave it… example /dev/emontx0 and /dev/emontx1

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Thank you.

This random USB port issue if I have 2 is not nice, so I can use only 1 USB port for sensors, it’s ok.
Can I use multiple serial ports?

Also not clear: If I want use ac-ac voltage adapter what is recommended, like this, recommend to use for both emonTx? It uses any additional port? If I use 1-1 ac-ac for 1-1 emonTx, it’s ok, good plan?

About different sensor input:
3 x single-phase CT current sensor inputs
1 x high sensitivity single-phase CT current sensor input channel (18.8A / 4.5KW @ 240V max)


Optical Utility Meter LED Pulse Sensor: Where should I use it? Recommended?

I show 2 type of CT sensor:
SCT-013-000 - max 100A what is recommended to high sensitivity single-phase CT input channel
and I see not in shop, but found in learn side:
YHDC SCT006 - max 20A? - recommended to NOT to high sensitivity single-phase CT input channel? In my view: SCT006 better, more precese for smaller than 20A measurement, it’s true? And this cannot measure more than 20A fine, only with mistakes?
SCT-013-000 recommended for main power line measure, like “all of energy usage” cable?
And advantage or good idea to use this SCT-013-000 for measure 0-16A? Or if I know all behind a 10A or 16A circuit breaker, I should use SCT006?
And on 2. emonTx at high sensitivity single-phase CT current sensor input channel I must use SCT-013-000 and I should measure what maybe will use more than 20A, right?

Sorry for lot of question.

The link Stephen provided explains how you can use more than one USB port.
It’s easy to do, and is reliable. Here it is agan:

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The port for the a.c. adapter is already fitted and available on the emonTx. It uses a d.c. barrel connector. The connector is “9 V” in this photo:

You can power the emonTx either with 9 V a.c. or 5 V d.c. To measure the a.c. mains electricity voltage, you must use a 9 V a.c. adapter.
You must use one a.c. adapter for each emonTx if you use that to power the emonTx.
If you use one 5 V d.c. adapter to power both emonTx’s, then you can have one a.c. adapter feeding only a voltage to be measured (not power) to both emonTx’s.
I advise you to keep it simple, and use one a.c. adapter for each emonTx.

You can add a resistor inside the emonTx to convert the high sensitivity input to 100 A, or any current you like greater than 18.8 A.

You can attach it to your electricity supplier’s meter, if it has a LED that flashes to indicate energy used. But if you have PV or generate your own electricity another way, it will probably NOT record the energy you export. This is because the LED on your meter will either not flash when you are exporting energy, or if it does flash, you cannot know whether the flashes means imported or exported energy. If it does flash only when you are using electricity, it will accurately record the imported energy that your meter records.

It is true, but the difference is very small, because the input of the emonTx is not intended for the SCT006. If you do not have space in your switchboard for the SCT-013-000, then you can use the SCT006. The maximum current for the SCT006 and the emonTx on a 50 Hz supply is approximately 16 A, not the 20 A that it claims. You should not use the SCT006 on the high sensitivity input - it will overload the c.t. and it will give large errors. It will be less accurate than the SCT-013-00 used in the same place.

Edit: If you have not already read it, look at the Conclusions to my report on the SCT006


You must not be sorry - we are happy to answer your questions. I know there is much for you to learn, we shall help as much as we are able.

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just for completeness, you can also look at the iotawatt device. 14 devices can be monitored I believe, but still not Ethernet!

I too would like distributed sensors over Ethernet as I hate wifi, but haven’t reached a solution yet, so the posts here have been helpful.

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if all you can not figure out Ethernet and are concerned about wired connection rs485 works fine as a second wired suggestion… I use it and it cheaper then Ethernet and easier to set up for the most part …

here example code from a blog - I would probably set it up as a request/send — the master requests from emontx1 and then it sends data- then it requests data from emontx2 and it sends data so you do not run into issue of over lap

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Both emonLib and emonLibCM naturally take readings at defined intervals, normally 10 s. No data is stored in the standard sketch, if the option to send data via the FTDI port is chosen, it must be buffered in the RS485 device.

However it would not be too difficult to develop a sketch that would report when requested, it would then become the responsibility of the Master device to poll each emonTx as necessary.

In the case of emonLib, the sketch would report the “instantaneous” values of power at the time of the request and the energy accumulated since the previous request; in the case of emonLibCM, the sketch would report the average values of power and the energy accumulated since the previous request.

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Yes, this is the most “done” solution what is open source what I found… so for this just I connect my current Raspberry Pi 3B PLUS (what have already Home Assistant) and I connecting to web service like Emoncms and influxDB same time? Or recommended to upgrade my hardware to Raspberry Pi 4B 4GB? Nevermind, i will see it.

Seems like this Iotawatt so similar to Open Energy Monitor project (similar forum, similar CT sensors, Emoncms support, etc). This have any connection about this 2 project or rival? I don’t want flame or something just asking what I don’t know yet.

Thank you the answers.
All getting clearer now.
So for each EmonTX I should get AC-AC adapter.
About SCT006 and SCT-013-000: For 1 high sensitivity input I will use SCT-013-000. If put the sensor after 16A or 10A circuit breaker, so not possible to be more than 16A usage, you recommend to use SCT006 or still use SCT-013-000?

I asking maybe 2 strange questions:

  1. Possible to someone solder / setup my config what needed, like 6-8 or 14-16 CT like iotawatt?
  2. Possible to be available iotawatt with Ethernet connection without Wifi? Or someone can made this changes with that?

I think aloud: Or because sadly I’m mostly a “software developer guy” not a “hardware soldering guy”, it will be more easy to me to get iotawatt, I can use 14 CT what is perfect for me, and I will use this already done product or someone or the manufacurer for extra price made me a version with Ethernet connection (adding Ethernet shield and just by software disabled Wifi, it’s ok for me). You think it’s possible?
Soldering this devices and wiring maybe many weeks of work for me, because I’m not professional about this. I finding the good but more easy solution. For example: I soldering, wiring emonTx devices, etc… and somone not working… maybe weeks for debug, etc… but if just after years iotawatt dies, i just order a new one if cannot fix and all working again, no need to soldering and testing, debugging for weeks.

Please don’t be angry with me for questions and for finding the best way for me.
Thank you for helping me!

Few people here know about and can support iotawatt. I suggest The IoTaWatt forum is a better place to ask a question that is specifically about the operation and use of IoTaWatt. That is managed by Bob Lemaire, its creator, and he and the other users there are more likely to have the specific knowledge to help you.

You will not have satisfactory results if you use the SCT006 on the high sensitivity input, unless you modify your emonTx.
With the other 3 inputs, it is your choice. You will have slightly better results with the SCT006, provided that the current always remains below 16 A. Remember that a 16 A circuit breaker will carry 16 A forever, and more than 16 A for a time that depends on how much above 16 A it is.