3.2 DME tester - my newest project

[ischmitz]

Rick, I assume what you plotted is a spice simulation, right.

The 3.2 ignition works just like a simple Kettering ignition. The only difference is that the points are replaced by the darlington transistor in the DME. It switches GND to the coil for the dwell time (charging it) and then turns off. There is a current feedback to limit the charge current through the coil.

Once the darlington turns off the magnetic field collapses and that is what produces the high-voltage spike on the secondary.

You shoud not measure any voltage across the coil with the engine not running since there is no current flowing through it. But both sides of the primary should measure 12 volts towards GND.

[James Brown]

closest thing I have to "realistic" is my "zenith".......cool stuff, keep it up

[rick-l]

I was wondering what the stuff in yellow did. To me, after some arduous calculations, I figure it limits the current to about 8 amps.

When you turn the ignition on is there a constant 8 amps going through the coil? (Before the engine runs)

EDIT: let me rephrase that. When you turn on the ignition does the DME wait for speed sensor inputs to charge the coil or is it always on?

[ischmitz]

The coil is only charged for the dwell time when the DME receives a signal on the speed sensor input. Else the Darlington is off the and the coil isn't charged. So with the ignition ON but no cranking the coil isn't charged.

And yes, the yellow box is a current sense-driven current limiter. The 0.05 Ohm resistor measures the current.

[rick-l]

Originally Posted by ischmitz

The coil is only charged for the dwell time when the DME receives a signal on the speed sensor input. Else the Darlington is off the and the coil isn't charged. So with the ignition ON but no cranking the coil isn't charged.

So the guy in the other thread you can conclude his DME is Tango Uniform if he sees 4.5 volts across the coil primary.

The other thing I was trying to figure out is that network down and to the right of the yellow box. It is obviously a network to keep the Darlington from going into deep saturation but I haven't seen anything like that before.

When you change T504 what parameter do you look at to choose the Select In Test (SIT) resistor R517? At least I think Abgleichwiderstand translats to SIT.


I can see R526 and R508 (both have A on them) would be selected to adjust the current.

[Wavey]

You guys are just making all this up, right?

[ChrisBennet]

Years back a started/tried to make something similar only using a PIC processor to make the timing and reference signal. Hat's off to you!
-Chris

[ischmitz]

I have seen PIC-based solutions from the Megasquirt crowd before. Quite nice but I simply don't have the patience to learn programming for these little buggers. See here for a superb example: http://jbperf.com/JimStim/index.html that can actually be configured without programming skills.

It makes my signal generator look like a stone age tool in comparison.

I also used the sound card for a 60-2 wheel before but then I always needed the PC next to the tester. Cumbersome, but it worked. See here: http://www.megamanual.com/router/crankwheelpulser.htm

[Joe Bob]

Smoke and mirrors.....he just does miracles.....

[McLovin]

Originally Posted by Wavey

You guys are just making all this up, right?

LOL.

That creation is damn sweet.

The function is unbelievable, but I also like the retro/mad scientist look of the contraption!