Is there a serial input available to connect the emonTx? Not as far as I can see.
(I’m looking specifically at the TP-Link “nano router”, not OpenWRT in general.)
I think you will find it has an USB port.
Thanks for all your comments guys. I have another question 
Am I right in thinking the voltages on the uart connector are out 3.3v ? I seem to remember reading that on a wiki somewhere.
In which case can I safely interface the emontx uart with a device that is based on TTL levels ?
I’m trying to create a test environment where I can connect the emontx to a windows pc and see the data flow.
https://www.rs-online.com/designspark/hacking-the-tp-link-tl-wr703n
Trust me it has a serial port, but you need to solder 3 wires to gain access to it. Very easy to do. The beauty is that you then have access to a small network connected Linux box that you can do so much with.
If you have a PC close by to your emontx then just plug the Serial Port into a USB UART and you should be able to read the serial port data directly.
That device can have OpenWRT loaded on it too. And I will bet it has a Serial port on board the PCB too, which is what the current USB is connected to.
I’m hoping to do some playing/testing with the data stream over the next few days.
Thanks to everyone who has offered me help on this so far. I now have a better understanding of what role the emontx actually plays in the open energy monitoring solution.
It has been quite a while since I did anything with this, but you may want to have a “programmer” as well - IIRC I used that to flash the EmonTX. Available from the OEM Shop for not-a-lot. Programmer - USB to serial UART - Shop | OpenEnergyMonitor
The thread that @borpin linked to above became hugely long, but in case it helps I did upload a How-To for Dummies guide here - Avoiding wireless connections - EmonTX serial RPiZero solution - #119 by haffle
Good Luck!
I second that. We always advise people to have a programmer. For the extra cost, it means that there’s a method available to diagnose faults or make adjustments.
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I just wanted to come back on and say “thanks” to everyone who responded to my question.
In the end I have gone back to basics and looked at what I was trying to achieve so I invested in an add on wifi module from the open energy shop (excellent service BTW). so I now have the emontx pumping data up to emoncms. Well, when I say data I mean readings with zeroes in because the emontx is on my desk and the clamps aren’t yet in place.
Understanding how this llot fits together is a big step forward to me so once again thank you everyone.
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