emonTX wierdness - works in lab, not in production

Hiya all,

Got my emonTX, built it and hooked the ct up to a 425W (rated at 230V, we have 240V here) heater sat next to me in my lab.

Had to figure out which pin to what CT connector and orient myself with the Arduino pin mapping, etc, etc. Once I got that sorted and understood I was receiving readings. Visited the calibration page and after a short while I was getting pretty accurate readings. Changed the load to about 1500W to check on linearity and all was good. I don't have access to an expensive instrument but the readings I got were pretty damned accurate for my needs. I get the readings back to a JeeLink module. All working very, very nicely indeed.

So, all fired up and happy with progress, I moved the unit to my house db board, clamped the ct, made sure we were safe and as unhindered as could be installing. I found an old 5v, 1.5A power supply that I modified to run the board from (connecting 5v and GND to pins 3 and 1 respectively on the FTDI header. Tested this rig in the lab before to ensure all OK and it was.

Fired it all up and rushed to my JeeLink to watch the incoming packets. I transmit a packet every 10 seconds. Packets start coming in BUT - with zero values ie. invalid data! This is the EXACT same rig hooked up to a heater in the lab that is now hooked up to the mains, but with zeroes instead of data. At the time, the Effergy shows an instant energy reading of around 1.1kWh.

At one point I was 'fiddeling' with the CT connector on the board and did get a reading or two/three. So, back to the lab and make absolutely sure all the solder joints were good and nothing untoward on the board. Then back to db board, connect - and still zeroes! When I hook it up to my lab setup it works perfectly, no issues, dramas or any other problems.

I took readings over the load resistor (just over 0v), over the divider network next to it, 1.6xxV, analog pin (1.6xxV), cleaned up (resoldered) the ct plug. All to no avail.

Please help by pointing me in a direction here. I fly off very soon and would dearly like to get this working before I go that I can build up 2 months worth of data to analyze when I get back. The 'other' meter is just too damned inaccurate, and they don't want to give me any info to help finally decode their stream - so the hell with them! I've got most of it decoded already, but really irrelevant because of it's inaccuracy.

Thanks in advance, appreciate any help.


Robert Wall's picture

Re: emonTX wierdness - works in lab, not in production

I am thinking r.f. problems.

Over what distance did it work in the lab, compared to in the field - is it within radio range?  Is there anything else nearby on the same frequency jamming the transmissions (the Efergy meter is alleged to be on 433 MHz)? You have an 868 MHz emonTx? (and in the sketch - I've found that setting 433 MHz in the sketch with an 868 MHz module will transmit to an 868 MHz receiver - badly over a few cm only!).

You might get some ideas here: http://jeelabs.org/2011/05/15/rfm12b-range-testing/  (You'd need to modify the sketch to use the serial output via USB, not the LCD of course). I've never used a JeeLink so I can't help much.


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