SparkFun Forums

[Quantum_Flux]

Greetings. I just changed a timing belt in a Geo Tracker, which was a huge joy (ha). I need to confirm and perhaps reset the distributor timing now though. I don't have $40 right now to get a timing light for 5 minutes of use, so I thought I'd waste $100 worth of time making one for $5. Which I think is possible.

My plan is to somehow switch a transistor to engage a white LED, which is bright enough to show the timing marks clearly. However this requires some kind of inductive coil around the #1 spark plug wire and the necessary electronics to get the impulse working well enough from that to switch the TIP120's base. (NPN).

I was wondering what might be needed in the way of coil turns, and additional transistors to amplify, or otherwise any other parts needed to tame the wild pulse (any pulse) coming off a plug wire. If anybody can suggest a route or contribute a diagram, would be super helpful. I made a mini-coil to wrap around the plug wire in a clampish sort of way, but there's no flick of my beast, and I could be sending > 5 V down the pipe too...for all I know. Or just .004 AC . I think it might need amplification. This is something I'm not experienced in.

A $5 timing light would be the do-it-your-selfer's pal. Any pointers to the correct path are welcome. I have tons of parts laying around, I just need a recipe, mostly for the impulse input circuit. (I think)

Thanks.

Robert

[LopeD]

the 555 can be good for that purpose. its trigger pin is very sensitive. if i were you, id set up a 555 in monostable mode, with a period of like 0.2 seconds or something, and run the trigger wire to a coil aswell as adding a big high resistance pot to it, like 100k ohm, 1m ohm, or 10m ohm.
remember to keep the trigger wire as short as you can.
might be able to just use a resistor instead of the pot, it should not be too critical.

ok, im just looking at my 555 book for you. they have a circuit (monostable) that gives pulses to one of those analog rev counters.
at 7000 rpm there is 4.3ms between pulses on a 4 cyllander car.
(2 pulses per revolution)

but it sounds like u only want to watch one spark plug wire, so i guess the minimum amount of time between pulses would be 8.6ms.

i guess you should set the period according to what RPM you're gonna be running while you're testing, longer periods are probably easier to see, so you might want to make it longer than 8.6ms.
anyway, the trigger section for their rev counter circuit (the part you need to copy) goes like this:

have a wire wrapped around the spark plug wire, (i dont know how long) with the end of it not hooked up to anything.
that coil is connected to the annode of a 1n4001 going to VCC, meaning if the trigger wire voltage goes above vcc, it get shorted to VCC.
then theres a 33k resistor going from the trigger wire to vcc.
and then theres another protection diode 1n4001 with its cathode on the trigger and annode on ground. that way if the voltage goes below 0 the trigger is clamped to ground.

pretty simple. you could use this small trigger circuit and hook it up to a PNP transistor. problem is the 555 needs the tinyest little current to trigger, so if you did it with transistors, you might need like 3. the ULN2004 might be good for that. personally id just use a 555.

hope that **** helps

peace

[upand_at_them]

Unless the Tracker is different than every other car, you shouldn't have to reset the timing.

In fact, the timing you're referring to is the ignition timing...The timing belt that you replaced ties the crankshaft to the camshaft. Completely different.

Mike

[Quantum_Flux]

Unless the Tracker is different than every other car, you shouldn't have to reset the timing.

In fact, the timing you're referring to is the ignition timing...The timing belt that you replaced ties the crankshaft to the camshaft. Completely different.

Mike

I'm very aware of the difference between camshaft and ignition timing, particularly after having done a big job like that. That does not change the equivalent fact that it's a good idea to verify it after as part of doing a thorough job. I'm just following the Haynes manual there.

However, more importantly from a maintenance aspect, the ignition timing on this vehicle has never been set nor checked once since I've owned the car (60,000 miles of my own over 7 years + 53K miles prior) and I'd like to know for sure that it is within specifications still, particularly after a big hernia operation like this one. Thus was begat the little mini-timing light project idea.

Robert

[Quantum_Flux]

the 555 can be good for that purpose.<snip>
ok, im just looking at my 555 book for you. they have a circuit (monostable) that gives pulses to one of those analog rev counters.
at 7000 rpm there is 4.3ms between pulses on a 4 cyllander car.
(2 pulses per revolution)

but it sounds like u only want to watch one spark plug wire, so i guess the minimum amount of time between pulses would be 8.6ms.

Big thanks for that handy info LopeD. That's a fine approach. This project doesn't have to just be for a car as here, but anywhere you need some inductively triggered something. Timing one's magnetic anti-gravity devices, etc.

As to car need, I would be checking the #1 wire.

The speed to check is actually at idle, 8-900 RPM, max 1800 or so. Another e-whiz I talked to suggested though that at the short pulse duration, I'd likely not get enough light out of an LED to even illuminate the timing marks. That's possible I'm sure. But I have a 3 pack from a mini-light that I think would do the chore if I can get them to flick. They are plenty bright and I don't need the sun here, since I'll be doing this in the dark.

Robert

[LopeD]

"Another e-whiz I talked to suggested though that at the short pulse duration, I'd likely not get enough light out of an LED to even illuminate the timing marks."

well, using the 555, you could add a POT to it to increase the duration that it keeps the LED on.
the inductive spike would trigger the 555, which would then stay on for it's timed period.
though you might not want the LEDs coming on for any longer than there is juice going into the spark plugs.

if the LEDs are on for too short a period, and they aren't making enough light, you could increase the current they are getting, the datasheet should be able to tell you the maximim current rating and for how long you can have this current flowing.
with the LEDs driven off the 555, you could set the 555 up in such a way(edge triggered) that the LEDs never stay on for longer than the timed period which you would set at some safe value so you dont blow them.
Some LEDs can take 1.5A for a few ms.

just a thought.
im an ex 555 maniac incase you didnt notice.

[LopeD]

if you really want to be able to see whats going on, do the 555 thing, get the xenon tube from an old disposable camera, one of the transistors from a old PC PSU aswell as the caps and rectifier... im sure you can figure out the rest