To achieve faster throttle response and less air resistance we replaced a standard Air Mass Volume sensor like this:

in a Porsche 911 (964 3.6L engine) by a newer type Bosch Air Flow sensor (HFC unit) like this:

Unfortunately the output signals don’t match and at that moment reprogramming the Motronic was not an option. So I decided to make a programmable converter which took the signal from the HFC unit and emitted a signal the Motronic would accept as valid input.

The converter unit was made with a PIC16F84 microcontroller connected to a Philips I2C PCF8591 8 bit AD/DA converter mounted in a sturdy metal box.

With a laptop and some special written software (with Xforms under Linux) the curve for the signal was adjustable by mouse and after some hours of tweaking, CO measuring and testdriving the best settings were found.