Hi Hendrya,

What sensors are you using for RPM counting ??

There can be mainly two problems which are corrupting your micro.

1. The noise in the power supply.

2. The noise in the sensor interfacing cable.


Let's discuss the things one by one.

First use the dry battery cells as you are already using. Put the circuit in a metal box, sheilded, as already suggested by others.

Now use opto isolators at the 8951 input from sensors. (depends what sensors are you using.)

If and when this isolation solves the problem then use the car's battery for the power supply but use it with the filter as suggested by Khalid Bhatti.

Hope above helps

Simon


PS:

Don't give your locked micro to Khalid, he will copy your code. hehehheheheheeee................