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Recent content by ziploc

  1. ziploc

    Spark plug wire inductive pickup for RPM

    Sorry for the delay guys. I'll try to respond to your questions here. I sure appreciate the tips. >> Grounding could still be a problem, because if your ground reference bounces up enough, the 5V signal will look like a 0V signal. Hmmm... It's probably a 5" wire between uC and display Gnd...
  2. ziploc

    Spark plug wire inductive pickup for RPM

    Thanks for the tip. I don't think that's an issue for two reasons. First, it works perfectly until I fire up the ignition system that it's measuring, and secondly because I'm not using the LCD backlight. But I can certainly measure the draw and voltage of the LCD and check the specs on the...
  3. ziploc

    Spark plug wire inductive pickup for RPM

    I think it's reporting RPM correctly because I'm recording the time periods between pulses and they're now very well behaved. I've been meaning to put it back on the scope and verify the periods recorded are in agreement with the pulses I see - but it seems unlikely I'll find an error there...
  4. ziploc

    Spark plug wire inductive pickup for RPM

    Or... https://www.dropbox.com/s/ba91zt1tez1uue9/As-built%20circuit.gif
  5. ziploc

    Spark plug wire inductive pickup for RPM

    Looks like that attachment didn't work. Let's try this:
  6. ziploc

    Spark plug wire inductive pickup for RPM

    Well, I've got the spark sensor working and I think it's reporting RPM correctly. But when I use it on my paramotor the LCD display goes completely bonkers. I imagine the noise of the spark is running through the circuit and doing horrible things. I'd appreciate any thoughts on how to solve...
  7. ziploc

    Using thermocouples?

    Yes, my CHT runs in the 200-240 deg-C range. I think I'm really liking the idea of putting the thermocouple through a simple op-amp (already ordered), and compensating for the cold junction using the temperature I'm already getting from the BMP085 (which I nominally use for altitude and...
  8. ziploc

    Using thermocouples?

    How do you feel about this op-amp: http://www.datasheetcatalog.org/datasheets/166/49945_DS.pdf
  9. ziploc

    Using thermocouples?

    Great. Thanks again. I've got some instrumentation amps from a previous projects, but they're very small surface mount components - so I'll pick up some DIP op amps. This is a 2-stroke engine that's running at relatively high performance, so it tends to run near enough to the edge that a 45...
  10. ziploc

    Using thermocouples?

    Thanks for the response Gunnar. I wondered about using something simpler, and there is in fact a Maxim IC that provides temperature compensation and A2D conversion. I would have to read that as I2C instead of analog (which I think is OK), the only down-side is that it's only available in a...
  11. ziploc

    Using thermocouples?

    I'm building a relatively simple circuit based on an Arduino to serve as a console for my powered paraglider. I want it to monitor RPM, cylinder head temperature, altitude, etc. At this point I have some questions about interfacing with the thermocouple used for monitoring cylnder head...
  12. ziploc

    Spark plug wire inductive pickup for RPM

    Thanks again for all the great info. This project is on hold for me again as I'm completely focused on the upwind cart thing. This weekend and next we've got the North American Land Sailing Association out to observe our record attempts to go directly upwind faster than the wind. Hopefully...
  13. ziploc

    Spark plug wire inductive pickup for RPM

    Thanks again. There's a surprising amount I don't know still. I'm reading up on this business of biasing and gain setting in the manner you describe. It seems like it should be obvious to me, but it's taking me some effort. Should I be asking these basic questions on a different part of the...
  14. ziploc

    Spark plug wire inductive pickup for RPM

    That's very interesting. If I'm understanding you correctly, you believe that the first pulse is the actual spark. Then there's a significant gap, followed by ringing in the ignition circuit - not in the detection circuit. I have to confess that I don't understand why there would be ringing...
  15. ziploc

    Spark plug wire inductive pickup for RPM

    Alrighty - a new (and now obvious) factoid was pointed out to me... No need to limit the positive voltage to the base with a diode - since the B-E junction IS a diode.
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