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|1||Honeywell HR20/HR25 thermostat||parts|
|1||Connector ISP 2×3 pin|
|1||Transceiver PCB RFM12B|
|1||Antenna (82,2mm wire)|
some thin short flexible wires to connect ISP and RFM12B with the PCB of the HR25 thermostat.
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).
Other resources dealing with hacking of HR20/HR25 thermostats: