Good Day All,
I have constructed a tachometer circuit using an LM2907 and it seems to be working when I have it hooked up to the coil in my car and the engine running (the voltage output varies with R.P.M. like it should). I wanted to calibrate it since I cant rev the engine to 7000 while in the garage so I built a signal generator from an NE555 to simulate the frequency output by the coil ,and that circuit works fine (I checked it with a real working tachometer).The problem is , when I try to use the NE555 circuit to provide pulses to the LM2907 tach circuit, it doesn't output any voltage and I dont know why or how to fix it. I think it may have someting to do with the signal shape but I'm only guessing.The tach circuit is shown below and any help would make my day.
I have constructed a tachometer circuit using an LM2907 and it seems to be working when I have it hooked up to the coil in my car and the engine running (the voltage output varies with R.P.M. like it should). I wanted to calibrate it since I cant rev the engine to 7000 while in the garage so I built a signal generator from an NE555 to simulate the frequency output by the coil ,and that circuit works fine (I checked it with a real working tachometer).The problem is , when I try to use the NE555 circuit to provide pulses to the LM2907 tach circuit, it doesn't output any voltage and I dont know why or how to fix it. I think it may have someting to do with the signal shape but I'm only guessing.The tach circuit is shown below and any help would make my day.
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