Next question, to power the emonTX via the RPi (so I only use 1 power supply), do I need to do anything other than remove the DC supply from the emonTX and connect the 5V from the RPi to the emonTX?
That’ll ensure each component gets enough current, but it’s also a good idea to bond
them all together via their respective “ground” connections to ensure a common earth.
The idea is to tie the components together via a single connection from each component, then
earthing that connection. The “connection” is usually a chassis or “frame,” but lacking that, the negative power terminal on each component can be used. Doing that keeps all of the voltages referenced to a common point.
It’s a lesson I learned when I did GPS testing for the USAF.
“Component” means the Pi, the emonTx, and anything else that is powered.
Connect the grounds from each device to a common point.
e.g. connect the negative leads of all your power supplies to that common point.
Bonding the various components to a common point ensures all of the signals are referenced to the same “ground.” That can help keep serial datacomm (as well as other electronic devices) from acting strange.
Grounding, or earthing, is for safety. Given the low voltages involved in an emonTx and RaPi,
there’s not much of a safety hazard. Nevertheless, it’s not a bad idea to connect the common point
to earth to keep static charge buildup to a minimum.
But practically, how would you do that? All 3 power supplies are plugged into the same power strip and the ground pins are connected. I cannot see that I can do any more.
What you must not do is ground one side of the a.c adapter if you’re using an emonTx V2, because that’s connected to the 1.65 V rail, though you can use one a.c. adapter with many emonTx V2’s (but not a mix of V2 & V3).
For all the rest (emonTx V3 & emonPi), the barrel of the a.c. connector is GND to the p.c.b., hence to any other device that’s connected via the RJ 45, the FTDI connector or the screw terminals.
I should have been a bit more specific with my description.
When I mentioned connecting the negative side of the power supplies together,
I took it you’d understand I was referring to the DC side of the PSUs.
Providing you have connected both the rx and tx lines of the serial comms, you can simply add a chip reset wire and use avrdude with rpi-avrdude as described in the rfm2pi wikis. I used to do it all the time at one stage.
Are you saying you are powering the zero from the ac:ac adapter via the emontx? I’ve never tried that as I expected the zero to significantly deform the voltage waveform at the very least.
IMO in all aspects the zero is superior to the esp method and factoring in the price and the sdcard, it’s still a winner. Even more so when hosting emoncms on it too (i know you prefer to seperate them though) for an all in one solution like an emonpi with 4cts for considerably less money.