How to talk to the emonTX V3 via the serial monitor

Hi,  So the emonTXv3 works, but I want to have a play.  Plug in the USB to UART cable, and expected the TX to run off of the USB power so I could see the serial output, but the RF transmission isn't running and nothing on the Serial Monitor in the Arduino IDE.  The docs say to remove the AC power, which I have, but the board seems dead.  How do you get to see the debug log on serial output to see the emon working?  I tried removing the AC - DC jumper but still no life.  Removing the USB to UART cable and a reset and it's back to life. I don't want to force upload the latest firmware incase it's not setup correctly and that destroys it.

Using a MAC with the UART driver loaded, it comes up as either /dev/cu.SLAB_USBtoUART or /dev/tty.SLAB_USBtoUART, tried with both but I was assuming the tty one is the right one.

The reason I'm wanting to play is I assume I need to calibrate it?  The readings are a little high, the Vrms is over 255 and the clip on meter I already have on the mains shows about 20% less power usage than the emon does.

Cheers, Darren

dkeverne's picture

Re: How to talk to the emonTX V3 via the serial monitor

Ah, facepalm!  Had the header plugged in the wrong way round.  Assumed the LED was meant to be up.  Seems to be doing a lot better now...

glyn.hudson's picture

Re: How to talk to the emonTX V3 via the serial monitor

Good to hear you got it working, we'll do some testing ourselves next week and check the voltage calibration

dkeverne's picture

Re: How to talk to the emonTX V3 via the serial monitor

Cheers.  I've set Vcal to 269.66 after some checks with my MM and the figures are closer.  I also tested 2 CTs on the same wire to a 100W bulb (with 3 windings) and they were showing different values, 310 - 318.  Is that normal?  I remember seeing a page with comparrison figures, do you use that to set Ical?  I'll do some more calibration tomorrow and see what it needs on each CT to get them to read the same.

Another odd thing I noticed, the 1wire doesn't work.  I tried with 2 different DS18B20's neither are recognized. Should the OneWire DS18x20_Temperature example sketch work with the emonTXv3?  I set the OneWire pin to 19 although that seems to be Analogue 5 for the power, so also tried digital 5, which seems to be data.  Not sure if I'm using the right port, or maybe I have that wired in wrong too :-$  I tested with VDD coming direct from the 5V supply also...

Robert Wall's picture

Re: How to talk to the emonTX V3 via the serial monitor

You can expect 3 CTs on 3 inputs to have slightly different Ical values. There's a 1% tolerance on the burden resistor and a 3% tolerance on the CT itself, so two CT's calibration values might be 8% different.

dkeverne's picture

Re: How to talk to the emonTX V3 via the serial monitor

Hi Robert, Since the 3 CTs, 1-3 on the V3 use the same Ical, is it worth trying to calibrate each CT fixed on a specific input to account for individual variations or is that going a bit too far ;-)  I think I ended up seeing +6% on one input and -5% on another, which might be stable over a wide range of powers so easy to balance out.

Robert Wall's picture

Re: How to talk to the emonTX V3 via the serial monitor

I'm answering pretty much the same question here: http://openenergymonitor.org/emon/node/3292

Yes, I think you do need separate calibration constants, and I've writtten to Glyn.

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