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I'm building a thermostat and could use a little help

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danrogers

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Hi all. I am building a thermostat for my new place. I'm using an arduino nano and a 20x4 lcd screen, with thermistors placed in about 6 rooms.

I have two questions at the moment - should I connect my low voltage ground (5v) to the ground on the mains feed?

Also, I want the wall thermostat to be powered at all times, looking at the schematic (attached) I think the power (at junction labelled LIVE) will only be available when the timer is operational? SO I will have to run 5 wires to my stat, permanent live, timer live, neutral and switched return and gnd?

I have also included the PCB layout if anyone is interested.
 
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What I might do,is convert the system to work like a normal wall termostat. Take a look here: https://wiki.xtronics.com/index.php/Thermostat_signals_and_wiring and take a look at the small pic. You would likely have to add a relay for this to happen.

Instead of using thermistors consider using Dallas 1-wire temperature sensors.

Check X2 (pin 1) and X2 (pin 4) and see if one side isn't grounded. One side of the transformer would be (C) and the other side (R, Rc or Rh)
A connection to (W) from (Rh or R) would turn on an added 24 VAC relay for heat. The contacts going where the X4 jumper is.

Your little box, can be considered a zone controller. Usually these are powered separately because they power dampers.

Think about your system, you could have a master controller and individual room controllers. The master can control all of the siblings, but the sibling can only control itself. Possibly just display current temp and setpoint and allow overrides up to 2 hours in 15 min increments. The master is responsible for scheduling.

RS485 is usually used for this with power supplied separately and usually DC. 4 wires. Half duplex RS485 and power. There is only one master.
 
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