------------C97520791D2377 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit I will protect my power supply against surges because this car is a really old one, a Lada 1500 if you know this model. I have a 12MHz portable scope so i went to the car, pulled out the wires from the car's battery and the distributor and attached is a sample of what i got when measuring the signal. It goes up from time to time to 40, 60v and also under 0 like you can see from the picture. It has no MSD or EFI. It is an old carburetor-based engine made in 1979. I will try to implement a simple CNY17 to protect the PIC input and try to count the frequency, see where it leads me. Thanks for your answers guys, you are great ! You have always guided me on the right track. P> Sounds like you're asking for 2 things -- power supply and ignition signal P> pickup. For the power supply, a 7805 can work well depending on how much P> current your circuit needs. But no matter what power supply you use, make P> sure you protect it against positive and negative spikes/surges, which can go P> to over a few hundred volts in an automobile, especially older automobiles. P> For the ignition pickup, you will need to experiment a bit as the ignition P> signal has positive and negative spikes, etc. You'll need to attenuate the P> signal, filter it, etc. A scope is very helpful here. But a better option P> is to take a tach signal off an MSD or similar if the car has one. I'm P> assuming you don't have an EFI system to get a signal from. P> One other thing you'll run into on older cars is a lot of ignition noise (from P> the spark plug wires), so you'll need to protect your PIC circuit properly P> and filter/decouple the power supply lines, etc. I've seen applications P> where this noise/EMI would shut down the PIC circuit. You'll also want to P> place the circuit in the cockpit rather than the engine bay to help reduce P> this noise. 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