I'm trying to build a tachometer from the electromagnetic noise emitted from a car's ignition coil... I've had some success in separating the signal from the noise but I'm kind of stumped...
After some experimentation with an oscilloscope it seems I get the clearest signal using one loop of wire, half-inch diameter. I'm connecting only one end, since it seems the signal becomes very weak if I ground the second end, and plugging it into the circuit like in the attached figure. I place the coil 5 to 15 cm from the car's spark plugs and connect it to the circuit via shielded cable.
The signal in question is made of very high frequency spikes which happen every time a spark plug is fired. On the scope they're so quick I can barely notice. I'm having a hard time because if I try to make the antenna more sensitive (winding more loops into the coil) it attenuates the spikes and they get lost among the noise... If I make it less sensitive the signal will be too weak to work with...
I did found another circuit using a similar approach, here: https://www.redcircuits.com/Page23.htm Unfortunately that configuration didn't produce good results for me...
What do you think? Is that a reasonable setup or is there some antenna or circuit configuration that could yeld better sensitivity to this signal?
After some experimentation with an oscilloscope it seems I get the clearest signal using one loop of wire, half-inch diameter. I'm connecting only one end, since it seems the signal becomes very weak if I ground the second end, and plugging it into the circuit like in the attached figure. I place the coil 5 to 15 cm from the car's spark plugs and connect it to the circuit via shielded cable.
The signal in question is made of very high frequency spikes which happen every time a spark plug is fired. On the scope they're so quick I can barely notice. I'm having a hard time because if I try to make the antenna more sensitive (winding more loops into the coil) it attenuates the spikes and they get lost among the noise... If I make it less sensitive the signal will be too weak to work with...
I did found another circuit using a similar approach, here: https://www.redcircuits.com/Page23.htm Unfortunately that configuration didn't produce good results for me...
What do you think? Is that a reasonable setup or is there some antenna or circuit configuration that could yeld better sensitivity to this signal?