Problem: How to add automation to existing HRV systems where no CAT5E cabling exists. The HRV has connections for Low-Med-High speeds, and the statets would be Off,Low,Med,High
Solution: Use RF-Solutions 008 series radio link
Issues
For the system to work with the transmitter not continuously operational the relays need use the latching option. This means that on each signal from the transmitter the relays will toggle state. As we know, toggling with no feedback is not deterministic, therefore we need a way of resetting all the realys before we send any commands (i.e. we always start from a known state).
RF-Solutions use the KEELOQ protocol which is a rolling key approach. If RF communication is lost whilst the TX is sending codes then there is a potential lost of synchronisation. In tests we found that the limit was 16 lost TX codes. However, once communication is re-established the RX will re-sync in one TX code. This means that one operation is lost and the next is sucessful.
Known State Solution
Route the 12V through the NC-COM connections of relay 4. In this way whenever relay 4 is operated the receiver will power cycle to a known state, all relays de-energised.
TX lost solution
If commands are sent thus:
- Operate Relay 4
- Wait 1 Sec
- Operate Relay 4
- Operate required relay
This means that the first operation is sacrificial, in that if an RX has been powered off for some time, the RX will synchronise and be in the right state for the required relay operation.