Hi Wood Gassers,
I have been beating on the automixer and I am convinced it is ready for others to play with a.k.a. I haven't been able to break it yet.
If you want one just send me a note. The lead time will be several weeks because I need to have more custom boards made. Pricing will be $350 plus shipping for the board, O2 sensor, servo, and mixing valve assembly. This is without the Arduino since many people probably have one. If you need an Arduino Uno it will be another $35.
Please note, The automixer uses an unheated narrow band O2 sensor so it needs to be in a running exhaust stream for about 2 minutes before it starts reading valid data. That is why on the 4kW I have a manual mixer for startups and the automixer for operation. The startup can be on gasoline or wood.