PZEM-021, not worth it


Testing this unit for few ours now, it seems that low range readings are not right. Instead of showing 0,01A, it’s showing double value, 0,02A… Again, having device that draws more than 0,1A makes it completely reliable and precise. I finally opened it to see how to pull ttl out of it, and it’s definitely not worth time and effort. Serial controller is based on Mega88, I don’t know anything about this chip. and board is high density smd, not very suitable for further modifications.

Edit: now I used multimeter, low end readings are ok, just ps I’ve used for testing is not performing well. So if you want passive display for your up to 20 Amps applications, 021 is way to go.


Way to get ttl, this guy already did it:


It’s a real mess, so that’s why I think it’s not worth a try. It will work, but on board wiring connections are not very promising for further usage. It’s easier to use PZEM004 without display in space restricted conditions.


Looks too messy for me to implement the ttl hack but that aside are you saying the data is ok at low current?


Yes, everything fine, very precise instrument.


We will see how much demand there is for 20A energy metering and then decide if we should include support for it in the app. Personally as I hate hardware hacks then I would simply use the Pzem-004. I can’t say as I have tested the accuracy in detail as our priority has been whole house monitoring to date.

For whole house the Pzem-004 is less than 3% higher than the electric company’s meter, hence we have -3 set with the slider / step widgets on the tariff setup page.

Hopefully in the next few days I will post up a “quick start guide” for the parameters I set from a clean install for our Pzem. This will then be followed up with a more detailed guide.

Note to self, most parameters are held on the server but some are not.

Do you have a 004 or just 021’s at present?


I have just 021 now, ordered 004 few days ago. I can sent it to you with power strip if you want to test it together with 004.


It’s up to you but it might take me a little while to carry out the testing.
I have hundreds of web pages to build about smart energy meters and home automation :slight_smile: