Tui has two Raymarine Autopilots. Autopilot A is a Raymarine 6001 which has a motor bellow driving the steering directly, the older Autopilot B is an ST4000 and requires a drive unit to be fitted to the wheel using some clamps and is there as an emergency back up. Tui does not have a wind vane steering system so having this redundancy is welcome.
Both have their own compass.
The way they were installed lead something to be desired to say the least. They could not be connected on the same bus as they would both be transmitting the same Seatalk commands, and so they were on separate circuits. As neither was connected to the wind instruments they could only be used on a compass heading and could not steer on the wind.
Fortunately Thomas Knauf has reverse engineered the Sea Talk protocol, and this had lead Jon Fick to develop a remote control using a PIC microcontroller. Now Russell has some experience with PIC projects, and had the necessary kit to program one and we were able to use Jon's c-code. Russell designed and made his own circuit board.
We only need to send two commands, to engage the autopilot and to switch it back to standby. As a side effect the unit also has a serial output which puts out the Seatalk sentences to a PC, which was handy for debugging some of our other Seatalk problems. More on that later perhaps.
Here is the unit Russell made
Here are the two waterproof buttons (Auto and Standby) mounted by the wheel. The switches are waterproof from the top, but one of them gave up after a season due to water ingress from below. Fortunately we bought a packet of 10 switch and they are now sealed from below. We also didnt use screened cable running from the control unit to the buttons. This is a mistake as stray RF from the SSB can trigger the remote on or off.