Well, thanks to some excellent reverse engineering work by OldPokey, I finally decided to get off my dead end and start the project I've been thinking about for two years, designing a replacement for the Tach Amp we all love to hate.

I've decided to use an 8-bit RISC microcontroller as the heart of the project. I have the breadboard complete, and have written the code to get the microcontroller talking to the tach gauge. I can sweep the needle to any value, and dwell at any point for any length of time.

Photos are below

1) Rough breadboard complete
2) Sensor interface built on a separate board.

Next step is to optimize the magnetic sensor interface circuit, then write the code to bridge between the sensor and the tach.

As an adjunct to this project, I'm thinking of designing a tachometer diagnostic tool. The tool would plug into the tach amp socket, and perform the following diagnostic tests:

1) Sweep the needle around the gauge to test the gauge and wiring
2) Indicate supply voltage within range with a green LED
3) Check magnetic sensor and wiring for open circuit - indicate with a yellow LED
4) Visually indicate pulses received from the pickup with a red LED that flashes at an engine speed dependent rate.

Using this tool, it would be possible to diagnose about 90% of the possible problems with the tach circuit. Would there be any interest in this as part of the tool rental program?

More updates as they develop.

Attached Thumbnails

   

__________________
Bob
'82 300D Petrol B-G Metallic