I also can't figure how Gray codes would be used. That's quite a bit of work you've outlined Roger!!!!
I'll add the things I've been thinking about.
1) Moving the code to the RP2040 from the Raspberry Pi foundation. This would make it easy to add a WiFi interface for remote control and display. The RP2040 is not very expensive, $4 without and $6 with WiFi.
2) Double up on a couple of the relays to approx. double break-down voltage on the higher impedances.
3) Build a 100 watt attenuator into the circuit. When tuning, the signal would pass through the attenuator with about 1 watt radiated when 100 watts is input. This makes sure the radio never sees high SWR and that the relays are now switching under high load/voltage. A circuit would compare the impedance on the input and output of the attenuator to do the tuning. The SWR bridge would be used to check the tuning when the attenuator is out of circuit. For an example of this, see the Icom AH-4. See ?. I believe the service manual is available on the groups.io site.
4) Maybe separate the tuner onto two PCBs. The one PCB would be the tuner and handle all the RF stuff with space left open for some of the RF enhancements. The second PCB would contain the logic. That would allow changes to be made without having to throw populated boards away.
5) The best place for a tuner is at the antenna feed point. So anything to support that is good.
The Yaesu interface is quite a bit more complex than the Icom. It relies on CAT commands blasting back and forth between the radio and the tuner. Sending serial data over long cables needs to be considered.?
73,
Chris, K9EQ
