Hi folks, hope someone can help me. The rev counter on my 1973 Daimler V12 has given up the ghost and the chip (I'm assuming that is the fault) is unidentifiable - the numbers on it are MIC 7303 (Smiths instrument). Does anyone know anything about this?
I have now decided to try to make my own. First I tried using a 555 monostable but the signal from the coil is too erratic and I found it difficult getting the needle steady. Now I'm trying with a LM2917 using the circuit below (taken from Texas Instruments data sheet) but it breaks down above 540Hz - on a V12 that's 5400RPM. Although the car rarely gets driven at those speeds I would like it to work reliably up to minimum 7000RPM (fsd). Is that the frequency limit for the LM2917?
I have tried playing around with some of the resistor values but they don't have much effect. I am still testing it on a breadboard using a square wave oscillator - still have to try it on the car with the coil signal. The ignition is electronic but the tach signal behaves like a points system with 60 or 80V spikes.
I have now decided to try to make my own. First I tried using a 555 monostable but the signal from the coil is too erratic and I found it difficult getting the needle steady. Now I'm trying with a LM2917 using the circuit below (taken from Texas Instruments data sheet) but it breaks down above 540Hz - on a V12 that's 5400RPM. Although the car rarely gets driven at those speeds I would like it to work reliably up to minimum 7000RPM (fsd). Is that the frequency limit for the LM2917?
I have tried playing around with some of the resistor values but they don't have much effect. I am still testing it on a breadboard using a square wave oscillator - still have to try it on the car with the coil signal. The ignition is electronic but the tach signal behaves like a points system with 60 or 80V spikes.