EmonTx v2.5 and throughhole kits

We've had quite a few people ask about the throughhole emontx v2 and emonGLCD's designs since we've moved away from stocking them in the shop and developed the pre assembled units. I've also had several conversations with people offline who said how much they enjoyed building the kits and encouraged us to keep supporting and stocking them. The challenge is the complexity of running an online shop with many different product lines and the additional workload of kiting and stock ordering - but it seems like it might be worthwhile for us to look into a way to make it possible.

The emontx v2 currently uses different 3.5mm jacks to the emontx v3 and emontx shield, It also required a different case which needed milling to use. To try and standardise on the components required I've been working on a new version that is designed to fit in the emonTH case that doesn't require milling and uses the higher quality 3.5mm jacks used on the emontx v3 and emontx shield.

As I got stuck in to the design I thought Id add the powering via AC circuitry that's on the emontx v3 and find a way of ensuring all spare IO is available + the addition of a row of terminal blocks with power, ADC's and digital IO breakout in much the same style the EmonTH.

The first revision of this new design is now available on github here:

and looks like this (im really quite pleased with how it turned out, there's something quite satisfying about designing and routing together a pcb, trying to find neat layouts and so on):

The main features are:

  • 2x CT sensor inputs using higher quality 3.5mm jacks used on the EmonTx v3 and emontx shield
  • 1x ACAC Voltage sensing and power input
  • Terminal block power, ADC's and Digital IO breakout + full spare IO breakout.
  • Onboard DS18B20 footprint
  • Based around ATmega328 + RFM69 core
  • Fits in emonTH enclosure

The main downside perhaps of this design is that in order to get it into the emonTH case I needed to drop the number of CT inputs down from 3 to 2, the thinking being that most applications are house consumption + solar pv. But Im aware that this does make is unsuitable for 3 phase application, we do want to develop a dedicated 3 phase board design with voltage sensing on each phase so perhaps that's the better option for 3 phase application than using the emontx.

I've sent off for a first prototype PCB from ragworm so will be building and testing this design hopefully next week. Id welcome thoughts on the design and any suggestions and may do another revision before getting these made in quantity.

Common component kit

The other idea we've had is that since the emonglcd and emontx kit share so many of the same resistors and capacitors we could potentially offer a general openenergymonitor throughhole component kit with enough of the common components to build an emonglcd or several emontx kits. Then alongside the common component kit would be the PCB and emontx/emonglcd specific components such as the LCD, connectors and perhaps the atmega. We're' just working out the pricing for this. This could be quite a good option for people who have good home electronics stocks of different resistors/capacitors and could simplify the kitting for us with just one kit with 10x 20x of all the different resistors and capacitors. Interested in hearing people's thoughts on the idea.


bruce_miranda's picture

Re: EmonTx v2.5 and throughhole kits

This is actually quite good. Could the inputs be protected like on the V3.4?

nrgbod's picture

Re: EmonTx v2.5 and throughhole kits

Keeping the option of building your own v2 is good to see but 2 cts and a pretty case v 3 cts is not a good decision imo. The reason I bought my 1st V2 kit was to monitor my standalone phase shift immersion diverter as it was not monitorable by the Current Cost monitor I had at the time. I wouldn't have bothered with the V2 if I had had to give up monitoring either pv or grid to be able to monitor the immersion. Form over function doesn't sit well with a self built kit imo.

Robert Wall's picture

Re: EmonTx v2.5 and throughhole kits

I see the phase of the CTs is inverted with respect to the original V2. Two effects: the installation notes become wrong, and should there be a fortuitous connection of the cable screen to the sleeve terminal in the plug, the screen will inject noise straight into the input, rather than into the 'earthy' bias chain.

The note says: "CT 1-3 23kW Max @ 240V with YHDC SCT-013-00 CT" Too much ctrl-C, ctrl-V !

What are your thoughts about including a filter to keep the digital noise from VCC away from AVCC? This seems to be the recommended technique for minimising the noise from the digital side - ref: AVR 042, AVR 465. In the first, the 'dirty' VCC is isolated from the rest by an inductor, and in the second, AVCC is cleaned up by a L-C filter. In both, the two supply rails are separately decoupled.

dBC's picture

Re: EmonTx v2.5 and throughhole kits

- ref: AVR 042, AVR 465.

And the datasheet for the part!  You can see some scope traces of it doing its thing in this thread:


davidoff's picture

Re: EmonTx v2.5 and throughhole kits

It looks really good! I like this design...

TrystanLea's picture

Re: EmonTx v2.5 and throughhole kits

Thankyou for the input everyone, Il take a look the CT phase, and review your thread dBC and will be looking again at the power supply via AC, test equipment on order (thankyou Robert). There might be a chance to squeeze the 3rd CT on there if I move the AC input to the bottom and extend the size of the board by the 5mm or so on each side as shown in the outline above. Well spotted about the notes on the schematic, I put a lot of work into the board design but less the schematic ;)

jmessenger's picture

Re: EmonTx v2.5 and throughhole kits

I am pleased that you're reconsidering the move away from kits.  Working on my installation renewed my skills in electronics construction from decades ago and I'd like other people to be able to benefit from the increased understanding and involvement which results from building your own unit.  Many thanks.

sheppy's picture

Re: EmonTx v2.5 and throughhole kits

I like the idea of something that exposes all the hardware for future add on's, maybe this could pave the way for a basic timer / relay add on, perhaps that's not economic as a kit but it could be an open source idea for those wishing to pursue it?

I have 3 ideas floating around in my head right now

1)separate inputs into EMONCMS for my fridge and PVR PC, so I can get a sensible standby power reading for checking everything that can be turned off is off when I go out

2)remote control of my SPA heater which is currently off overnight and during the daytime when the sun isn't out.- this would allows me to set a low standby temperature and only heat it when I'm about to use it

3)remote control of HWC heating from the grid so if its not warm enough at the end of the day as detected by a sensor half way up the tank, it turns on for just long enough

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.