I went ahead and ordered this piezo pickup from a chinese vendor:
http://www.ebay.com/itm/350928303408Guitar bridge style. Stick rather than disc piezo. I've heard of watchmakers building a jig to rest the crown of a watch on the middle of one of these to do beat analysis.
Anyway, I'm guessing that if i hook this up to one of my oscilloscopes i will be able to view injection pulses and derive exact timing.
Further, I bet i could plug it into a PC microphone input and use pc o-scope software.
Surely others have tried something like this?
I've been working on getting an arduino to sense the TDC and injector pulse.
But the line pulse detector only works up to about 2000RPM,.. I believe it's because the line doesn't have time to shrink and expand at higher RPMs.
I've been thinking about a light sensor in the glow plug hole or a sound detector on an injector.
Why isn't anyone else trying something like this? Well, we don't have oscilloscopes for one. Number 2 is that some of us have laptop computers that are needed for work and taking them out next to the shake rattle and rolling diesel engine bay is not going to happen. If it goes slippy slide off the fender, my goose is cooked. No more paycheck until it gets back on line. #3 skillset, I came about the thickness of a thin capacitor away from going to school to become an electrical engineer but liked breathing fresh air and the woods more. So Forestry got my attention.
So keep working on this and let us see what you get. Could be really valuable to some.
Fatmoblie: Not sure I agree with the pulse line detector working up to 2K and then not. The TinyTach pickup on the injection line gives firm and great readings, increments of 10 RPMs way up to 4K. Then I take my toe out of the firewall. If you want to try the photo method I will wish you luck. The SnapOn Lumey tool went the way of the dino and was replaced by that there pulse line method. I have the adapter you speak of and the conversion box to fire off the inductive timing light. I found it on Craigslist a state away from a guy that was selling out his automotive repair business. He wouldn't sell it to me unless I called him first because it was a tool he purchased like 25 years ago and used once. So he wanted to be sure I knew what, how and why it worked. He didn't want negative feedback. The trick to that tool is that there is a piece of glass glued into the stainless steel tube and can withstand the pressure built up in the cylinder without blowing the glass out or apart. Something few seem to have mastered.
So you might have better luck going the sound method.
Later
I've been working on getting an arduino to sense the TDC and injector pulse.
But the line pulse detector only works up to about 2000RPM,.. I believe it's because the line doesn't have time to shrink and expand at higher RPMs.
I've been thinking about a light sensor in the glow plug hole or a sound detector on an injector.
My diesel pulse adapter with piezo injector line pickup will give an accurate pulse up to the rev limit, as will the Tiny Tach with piezo line pickup.
I'm not familiar with the Tiny Tach pickup. I'll have to look into it.
I'm not a real EE i just play one from time to time. But i do have multiple o-scopes for some reason.
I wonder how clean of a signal i will get from the piezo stick attached with just a rubber band or something to one of the injection lines.
I also wonder if it'll be too long for that in it's stock configuration, but i have a suspicion that a high speed abrasive wheel can cut it down without rendering it inoperable. At any rate, it is cheap.
Well the piezo pickup arrived yesterday. It's a steel channel with six sticks of piezo material attached inside with double-sided tape, probably soldered to a strip of metal, and then over top of them is a strip of copper. I guess it's hard to visualize and i should take a picture.
Been looking at the clamp-on pickups that diesel tachs and timing adapters use and I'm not really clear on how they are designed. The early snapon transducer has four flat sides where it clamps around the injection line, the rest seem to have two half circles.
anyway, 1 or 2 of the chips in the 3-inch stick may be enough, zip tied to an injection line, to hear the nozzle do it's thing.
If i were really good at electronics, perhaps i could build a simple circuit that amplifies the signal from the piezo to pulse a big white LED. Simple timing light. Who knows.
Lotta sensor/pickup info in the patents over the years, easily found at uspto.gov.
The simple trigger sounds nice, but I'd be concerned about noise and calibration, so an arduino might be the ticket.
I've been working on getting an arduino to sense the TDC and injector pulse.
But the line pulse detector only works up to about 2000RPM,.. I believe it's because the line doesn't have time to shrink and expand at higher RPMs.
I've been thinking about a light sensor in the glow plug hole or a sound detector on an injector.
My diesel pulse adapter with piezo injector line pickup will give an accurate pulse up to the rev limit, as will the Tiny Tach with piezo line pickup.
I'll have to work with mine again.
I rebuilt the 4-stage op-amp circuit inside the ferret and ran the result to the arduino.
It loads into excel using PLX-DAQ, where it gets plotted.
It registered at lower RPMs but got weird at higher ones,... I figured it was because the line wasn't shrinking enough between pulses.
I haven't really looked at how the ferret operates at higher RPMs with the timing light.
Haven't worked with it much this summer. More of an indoor project.