Amplify a signal from an inductive capacitive probe

[diif]

I've been handed a Hantek HT-25 inductive capacitive probe. http://hantek.eu/auto-ignition-probe-ht-25.html
My friend bought it as he has a motorcycle dyno and his old probe for detecting HT pulses failed.
Not knowing much about circuit design I'm wondering if it's possible an op amp circuit could be used to boost the signal so his current dyno can read the pulses ?

Any input would be appreciated. Thank you.

[eccerr0r]

Re: Amplify a signal from an inductive capacitive probe

Appears to be for an oscilloscope, so it should be just fine to build an op amp circuit.
Since it's for a scope, probably best to try to maintain a 1MΩ input to the op amp.

Unfortunately not enough info about what the expected output voltage should be, so no design guidelines available other than the input impedance.

If you have a scope, then this would make it easier to design a circuit... and also knowing what the target device/output requirements are is the other problem.

[Bill122a]

Re: Amplify a signal from an inductive capacitive probe

OP AMPS gain is set by the ratio of the feedback resistor and the input resistor from the output to the negative input.I suggest an npn transistor instead. you need two stages to avoid inverting the ignition spike

[Bill122a]

Re: Amplify a signal from an inductive capacitive probe

Try using a regular scope probe, holding it against the plug wire insulation, tape the probe tip and place it near the plug coil or wire for loose coupling. ITs no tcalibrated but it will show a fouled plug

[stj]

Re: Amplify a signal from an inductive capacitive probe

hantek only makes one scope for a car - download the manual for the input range.

[diif]

Re: Amplify a signal from an inductive capacitive probe

I spoke to the guy last night, his custom dyno machine has 5v on the plug connector. He was saying he's like the signal to be as close to the 5v as possible taking into account loss. He also said when he did a quick test with the probe on a bike with his oscilloscope it was showing "a blip one square high, 50mV ?" he was a little under the influence but it's not very big.

This circuit is just required to amplify the signal so the pulse can be picked up by the dyno for timing, the specific value of the voltage is not important.

Thanks for your interest so far.

[eccerr0r]

Re: Amplify a signal from an inductive capacitive probe

Losses aren't that big if you're using copper wire since the current is very low. If it's 50mV and you need 5V P-P then you need ~100x gain (probably a bit less than this is still okay), so it shouldn't be too difficult to build an op amp circuit with this gain.

[stj]

Re: Amplify a signal from an inductive capacitive probe

feed the opamp into a schmitt triggered buffer like a 74ls14 - that will give you a clean 5v squarewave.

[redwire]

Re: Amplify a signal from an inductive capacitive probe

The Hantek probe is linear with 1000:1 attenuation, so 1V/kV into a scope. Not sure if x10 or x1 1MEG scope.

If you just need a trigger pulse, I think you already have a few volts of signal (kV) at low current, enough to turn on a transistor or Schmitt trigger gate or 555 timer.

A problem is ignition firing voltages are full of ringing and RFI, they are not a nice pulse by any means. So you need some filtering.

Some ideas here: http://www.sportdevices.com/rpm_readings/index.htm