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Modification of Honeywell HR25 thermostat

to do

Needed Parts

You need a Honeywell Rondostat HR25 thermostat. It costs about 30,-EUR, but used items away for sometimes as low as 15,-EUR at ebay/amazon .

Partlist (in buildup order)

Amount Part Picture
1 Honeywell HR20/HR25 thermostat parts
1 Connector ISP 2×3 pin connector_isp.jpg
1 Transceiver PCB RFM12B ic_rfm12b.jpg
1 Antenna (82,2mm wire) antenna.jpg

some thin short flexible wires to connect ISP and RFM12B with the PCB of the HR25 thermostat.

Integrate it into a housing

The RFM12B fits well inside the thermostat housing between display and PCB. If a 2×3 PCB-pin connector is used for ISP, it is possible to hide it behind the turn wheel. This way it it easy accessible for reprogramming and there is no need to modify the housing or PCB1).

Wiring of ISP and RFM12B

to do

Flashing the firmware

to do

An other option would be to sacrifice the JTAG connector, cutting and wiring some connections.
hr25_thermostat.1383556935.txt.gz · Last modified: 2013/11/04 10:22 by GoHoHa