Hi,

The sensor that I am using is made by Allegro with part number: A3240EUA. It is wired as they suggest in the datasheet with a 100pF capacitor across ground and supply. After the trouble with interference in the garage, I decided to solder a second 100pF capacitor across ground and supply. For some reason this sorted out the problem and it isn't doing its own thing anymore. When I wave a magnet in front of the sensor, it seems to be giving a sensible reading.

After this (small) success, I decided to hook the tachometer up to an engine to see what it would do. I have installed a small magnet in the flywheel of the engine. When I flick the engine over by hand, it reads as it should, but as soon as I start the engine, there is another problem. For some reason the LCD basically just turns off, or the display goes extremely dull and it stops reading the RPM. One slightly 'suspect' part of the installation is that it is quite close to the ignition points on the engine. These points do have a tendancy to spark and I don't think that helps much. Tomorrow I will try and set something up to test the tachometer without the 'violent' ignition points right next to the sensor (using an electric motor or just a human powered device).

Does the hall sensor that I am using seem suitable for the application? The reason I ask, is because I honestly had no idea about them, so I briefly looked at the datasheets and then selected one from the list...

Warren