wdperry@ducvax.auburn.edu (05/11/91)
I need to build a device, using an inductive pickup like a timing light, that will give a single clean pulse each time the spark plug fires. Pulse needs to be at least 3.5 volts. It must be used on the spark plug side of the ignition not on the coil side. I have looked at the signal from an inductive pickup on the plug wire and it is pretty messy. Is anyone aware of acircuit that would cleanup this signal and output a single pulse for each firing of the plug? +5 volts is available to power any chips if necessary. Any and all suggestions would be appreciated. Thanks, W.D. Perry wdperry@auducvax.bitnet wdperry@ducvax.auburn.edu
whit@milton.u.washington.edu (John Whitmore) (05/12/91)
In article <1991May10.164429.4146@ducvax.auburn.edu> wdperry@ducvax.auburn.edu writes: > >I need to build a device, using an inductive pickup like a timing light, >that will give a single clean pulse each time the spark plug fires. Pulse >needs to be at least 3.5 volts. It must be used on the spark plug >side of the ignition not on the coil side. The problem is not so much lack of signal as it is the waveform (lotsa jaggies). So, use a one-shot (monostable multivibrator, like a 74HC123). The first transition will start the output pulse, and until the pulse is finished, NO OTHER TRANSITIONS on the line will have any effect. For something like a spark plug, there is a fairly slow firing rate (7000 RPM on a four cylinder engine would only be 17 milliseconds, and more cylinders or slower revs would be longer time). Just set the monostable time constant to 10 ms, and you'll get clean pulses from dirty input. Of course, you should be sure that the transformer secondary is loaded with a low impedance (so the spark won't be slowed by the transformer). Best way to do that is with a diode-clamped transistor inverter; when the transformer output is (+), the base-emitter diode is forward biased; when it is (-), the clamp diode (connected from base to emitter) is forward biased. John Whitmore
tomb@hplsla.HP.COM (Tom Bruhns) (05/14/91)
whit@milton.u.washington.edu (John Whitmore) writes: >will have any effect. For something like a spark plug, there is >a fairly slow firing rate (7000 RPM on a four cylinder engine >would only be 17 milliseconds, and more cylinders or slower ^^^^ John, I think you're slipping... >revs would be longer time). Just set the monostable time constant >to 10 ms, and you'll get clean pulses from dirty input.