Getting Started, a few simple questions

Hi, complete newbie to this, but experiance in electronics, PICS and programming in general.

Just putting together my raspberry pi, emonglcd and emontx, for a solar PV/pool monitoring setup, once I have it working on the basics I want it to do the following:-

emontx number 1 monitors solar PV and house power use (2 x ct clamps), located next to pi

Monitor solar output, and if it is > 3kw (regardless of house consumption) then turn on something for a minimum of 15mins, then turn it off when output drops...

have a second emontx some 40meters away to monitor a few (6) temperatures and another solar PV input and heat pump current consumption (2 x CT), this is also the location of the switch that I need turning on/off.

What is the range of the emontx and assuming it is < 40m, can I cable them together over that range and how?....can I switch something on/off on the second emontx based on the first emontx values?

also, where do I look to set the switching code/programming, on the emontx or on the pi?

I am sure it all all get simpler once I have it soldered and running.

Thanks in advance.

Robert Wall's picture

Re: Getting Started, a few simple questions

It would be a bold person who could say what range you will get. See here. It depends on whether you have a clear line of sight (when you should be OK for 40 m) or whether you have walls to go through - and then it depends on the material and thickness. And whether there are interfering signals in the locality. If you dig deep into the programming of the RFM12B module, you can slow the data rate and improve the range, but there's an obvious trade-off there.

The emonTx will receive, but it must (due to limited battery life) run on mains power to do so. You'd need to develop your own communications protocol and software sketches to exchange the data, as all the RF uses the same channel and collisions mean lost data. In the standard setup, the RF links are:

  1. EmonTx -> emonBase + emonGLCD (power, current, voltage, temperature)
  2. emonBase -> emonGLCD (time)
  3. emonGLCD -> emonBase (temperature)

I would generate the on/off command in the emonTx where you measure the solar power, and send an on-off command. If you must use wires, then that should be easy enough - I'd run a twisted pair of wires (telephone cable). There are spare I/O pins and provision on the emonTx PCB for header pins or sockets - just add a socket (or a plug). That should be good for well more than 40 m. At the receiving end,  I would drive a triac via a zero-crossing driver IC - exactly like Calypso-rae's immersion controller to switch your load - either driven directly from the remote emonTx if you're using wires, or if the radio works then from the emonTx that's local to the load.

mattnj's picture

Re: Getting Started, a few simple questions

thanks. i will keep you posted

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