UART - USB - stuck?


Just got a EmonTxV3 and I’m using UART > USB to talk to it.

Connection appears to work as I get

emonTx V3.4 Discrete Sampling V2.30 RFM69CW
POST…wait 10s

From it… but nothing more.

I’m using AC power adapter with JP2 in place.

I have one CT plugged in (but no cable through it)

Any ideas?

Sounds like the sketch is halting at the RFM initialization, have you changed the sketch or is it as supplied?

Does the LED flash after the emonTx has “stopped”?

You could try updating the firmware but If you have only just taken delivery and not changed anything there maybe a physical defect with the RFM circuit, if so you should email the shop support.

No changes from delivery

LED is constant

Oh dear ;-(

Hi Gary, it sounds like you have a faulty RF module. The sketch is hanging at the RF initialize section. We will send you a replacement on Monday morning. Very sorry about this. Please confirm this fixes the issue.

Please note that the new emonTx will have newer firmware which will talk at 115200 serial baud

I got a replacement unit which initially gave me


But after increasing the baud to 115200 it works correctly.

No EEPROM config
RFM69CW Node: 8 Freq: 433Mhz Group: 210

POST.....wait 10s
'+++' then [Enter] for RF config mode
CT 1 Cal 90.90
CT 2 Cal 90.90
CT 3 Cal 90.90
CT 4 Cal 16.67
RMS Voltage on AC-AC  is: ~265V
AC-AC detected - Real Power measure enabled
assuming pwr from AC-AC (jumper closed)
Vcal: 268.97
Phase Shift: 1.70
CT 1 detected
No temperature sensor

Fan heater on, half power, fan only.

Only question remains why is VRMS so high?

We’re normally about 248v here, I assume its a float as an int so 268.18 but even so its 20v higher than I’d expect…

Ideas or am I being silly?

How are you getting the a.c. voltage sample? Is it with a “shop” UK adapter or something else?
(Your assumption for the voltage is correct, it’s sent as an integer and scaled × 100.)
Can you measure the voltage from the a.c. adapter? - it should be 11.6 V ± 3% with a 240 V input on no load.


Yep ‘shop’ bought AC adapter

Shows 12.1V AC when I meter it which is above 11.6 V ± 3% (mains at the time was 243V)

Its not overly concerning unless it’s being used to calculate the watts (which I suspect it is…)

Spec on top of the plug says 230-240V AC so maybe just a case of to many incoming V’s?

The output is directly proportional to the input (until the core saturates), so at 243 V, I’d expect 11.75 V, so yours appears to be exactly on the upper limit of tolerance. Then there’s the tolerance of the divider chain inside the emonTx to take into account (1% resistors), so if both of those happen to have gone the wrong way, that accounts for another 1.83%, and the 3.3 V supply could give a further 1%. All that adds up to a possible error of 6.83% worst case, so if your numbers (reading 268.4 V with 248 V in are accurate, something somewhere is out of tolerance.

The voltage is used to calculate power, so if you’re sending the values to emoncms, the easiest place to adjust the calibration is there, either in emonhub.conf (if it’s a local emoncms) or in the Inputs section if it’s Alternatively, and if you have a programmer, you can go through the calibration procedure and adjust the calibration constants in the sketch.

I won’t flag this as a manufacturing fault just yet, as I’m using your [quote=“wuciwug, post:7, topic:2381”]
We’re normally about 248v here

at face value as the supply voltage when calculating overall error.