I’ve finished (eventually) the pics and write-up of Keith Doxey’s interface between my central heating and HomeVision…
“The switch mounted LED’s are fed from the 12 volt supply via resistors R1 (Downstairs Zone) and R2 (Upstairs Zone). HomeVision pulls Port A3/A4 low when the heating is OFF which short the LED side of the resistor to ground, this extinguishes the LEDs. The relays are fed from the 12 volt supply and are grounded by Port A1/A2 going low to operate the relay. This turns the heating ON. The mains side of the relays are wired in parallel to the existing programmer contacts and the programmer is set to OFF. In the event of HomeVision or Relay failure the existing programmer can be switched on and conventional heating control is instantly available. As the relays are connected to 240V AC is important that all connections are insulated using heat shrink sleeving and the enclosure containing the relays is only accessible by means of a screwdriver.”
Click here to see all the pics, circuit diagram and write-up HomeVision Heating
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