Random CT Readings on emonesp



I used the arduino shield as my input for the CT sensors. I got the kit where I had to solder the components on.

All seemed to go ok, set up a nodemcu board as the wifi interface, but my CT readings don’t change, they just stay at what the screenshot above shows. Even when nothing is connected, Have I screwed up somewhere?


Edit - moved picture from 3rd party site to OEM. BT

Do you have a usbserial programmer?

If so what output are you getting at the 6pin header of the emonTxshield when you disconnect the emonesp? This test should tell you if it’s the emonTx shield or the emonesp that isn’t doing it’s thing correctly.


Unfortunately I don’t, will look into getting one :slightly_smiling_face:

Also realized I’ve soldered the connectors on the wrong side :pensive:

You’re not the first. There is an alternative quick fix to avoid removing all the connectors that basically involves soldering some small link wires to the pcb at the (upsidedown) connectors to link the ring and tip pins.

[edit] - See First open energy monitor project (PART 2) | Archived Forum there is a picture of a pcb with the links drawn in about 2/3 of the way through)

[edit2] - better still, here it is

Sorry for the delay in actually getting back on this, I managed to get the CT1 and CT2 connectors orientated the right way. but it still shows the same values :frowning:

The silly questions first:

Can you check continuity between the connector tags and the burden resistor (the larger next to the back of the connector), just in case you have damaged a track?

Was the c.t. plugged in before you powered up?

Do you get the same result with all four inputs?

If you put a multimeter across the burden resistor, you should read 33 Ω without the c.t., and about 25 Ω with the c.t. plugged in.
When you power the Shield, you should read 2.5 V d.c on both ends of the burden (and both tip and sleeve of the socket). You should also have 5 V on the pin of the 3x2 header nearest the a.c. input.

Hi,thanks :slight_smile:

The restance values check out on CT1 and CT2 with 33 then 25 with it plugged in.

I get the 5V on the 3x2 connector, but no voltage across the resistors, if the sensor needs connected for this then thats probably why (i hope).

I flashed the serial only arduino code to see if that helped, can see the results below with the AC adapter connected. Is a CT connector in CT1 and none in CT2


[Edit] I’m guessing this means the issue is with the esp/uart output rather than the shield/arduino?

I was being an idiot, connected the AC adapter to the jack on the Arduino not the shield… Apologies

Revised figures

First no AC adpater
Second with AC adapter


Yes, you do need the c.t (or even just a plug) plugged in to see the midpoint voltage.

It does look as if the Shield - Arduino combination is working correctly. At this point, I must bow out, because I know nothing about the emonESP, and leave this to someone who does know.

Thanks, you’ve been a great help checking all the bits and narrowing it down to a specific part. much appreciated

Done some more fiddling about with it, seems the TX pin wasn’t connected (probably my bad soldering) so ran a cable from the arduino’s TX connection pin to the UART one and its working now :slight_smile:

Now just to try and work out the ESP, and getting it all connected up. With the cloud etc, what i don’t get is how the vrms is 280, surely that should be like 230 for the uk?

That’s a calibration issue. Ideally, you should calibrate the Shield with all its sensors in place on whatever will be used as its host, because accurate calibration depends on the sensors, the components on the Shield and the reference voltage of the host Arduino. The last is most likely the major contributor, because although the stability is good, the uncertainty in the initial value is about ±10%, followed by the a.c. adapter at ±3%. All the instructions are in the ‘Learn’ section.

(Note: the “standard” UK voltage is still 240 V - mine has varied between 231 and 245 over the last week. )