Electronics > Projects, Designs, and Technical Stuff

Transients in Automotive Inductor Signal

(1/5) > >>

SugerSquirrel:
    Thank you for taking the time to view my post. I have a few questions regarding a project that I am working on. In this project I am monitoring the signal from an automotive inductor negative terminal via a microcontroller. I am monitoring the signal, at the microcontroller input, on my analog oscilloscope. I have built the circuit, see attached files, on a custom breadboard which is able to handle higher currents and voltages.  I am able to run this circuit connected to a "high energy ignition" on a distributor test machine to simulate a real world application. The circuit is 3ft away from the machine during test and I am using 20 AWG wire from the inductor minus terminal to the circuit as well as the 14.3V and ground leads from the ignition to the circuit.
      Above about 6400 rpm all the way through 9000 rpm the signal is solid w/ no problems.  Below about 6400 rpm I have a good signal but I am getting transient  triggers that I can see occuring on my oscilloscope between the expected cylinder firing times. I am not sure what I can do to fix this.  Is there any additional filtering that I should be adding to this circuit? I am looking for suggestions on avenues to try to solve this as this is getting above my skill set.

      Thank you in advance for all your help.

        Squirrel

bdunham7:
Are you looking at the pickup coil on a GM HEI distributor?  If so, is it fully operational (plugged into the HEI module, HEI module energized and connected to the coil where it produces a spark someplace...) ??  Or is it just the pickup coil without the other stuff installed?

SugerSquirrel:
This is coming from a fully operational HEI as it would be in the car (Pick up coil, module, wire harness, in cap coil).  I am not taking the signal from the pickup coil, I am taking it from the in cap coil minus side.  I need to do this from the coil minus side of the coil.   I understand it is a bit easier to do it that way(pickup coil) but I know you can do it from the coil minus side and I was up for the challenge.
   Thanks for your reply.

    S

floobydust:
The coil primary waveform is complicated, it spikes up to around 400Vpk and then there is the plateau depending on the spark duration, and ringing afterwards, then starting over again repeating the dwell period. So your circuit must tolerate 500V spikes, and debounce the ringing. The debounce time depends on the #cylinders and max RPM.
I use a couple transistors to do this. If you are really worried about cost, you can run it into the MCU after a voltage divider/clamp/RFI filter, and debounce in firmware.

Your signal filtering circuit I would say is missing a -ve clamp diode for the transistor E-B, you don't need an EMI filter after the transistor and the 100R resistor is wrong. I find 5W zeners don't work as expected because they have large capacitance. Anytime I tried to trigger off the HV spike, it was difficult because the ringing can go over the initial spike, say 125Vpk and it triggers twice.
So I have best luck looking for fast +dV/dt portion and ignoring anything after that for a several msec.
edit: schematic jpg was corrupted, fixed

Circlotron:
One approach that worked well for me is have a comparator that triggers at +200V from a resistive voltage divider (no zeners) then feed the comparator output to the micro. Have a micro output trigger a 555 monostable that drives a transistor to clamp the comparator output to ground for 1mS or slightly greater immediately the circuit is triggered. This will make it ignore any noise pulses until the monostable times out. You could increase the monostable time to just a little bit less than the pulse repetition period at max rpm. Ignitions are fun!

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod