3.2 DME tester - my newest project

[ischmitz]

I finally got my newest project to work satisfactory - a 3.2 DME test station. I built it into an old discarded power supply box I got out of the junk pile where I work.



The tester simulates all inputs to the DME and is able to test all outputs. Here are some specifications. It can simulate the following inputs:

- reference and speed sensor 0 - 8000 RPM
- cylinder head temperature (CHT) sensor full range
- O2 sensor signal rich, stoichiometric, rich
- idle switch
- wide open throttle (WOT) switch
- intake air temperature (IAT) sensor full range
- air flow meter signal (AFM) full range
- cranking signal

The monitored outputs are:

- injector stage into an inductive load simulating the injectors
- Ignition into an ignition coil and spark plug
- RPM signal
- DME relay signal into a relay and indicator
- Idle control valve signal into an ICV

All important outputs and the reference signal are available on BNC connectors on the front panel for easy access with an oscilloscope. Let the testing begin. With this tester I can visualize and display the idle feedback behavior, spark advance in relation to the RPM and AFM signal, cold start enrichment, the O2 sensor-related mixture control, deceleration fuel cutoff, WOT spark advance and many more things.

Ingo

[88-diamondblue]

That is just awesome.

I'll be the first in line to send mine if you need another one to test since I am having a problem with my car running rich and haven't found anything that tests bad yet.

[saint914]

Hi, that's great, think of the fun you can have simulating different temp and load paramaters.....

[gregwils]

I am envious. I wish my brain was capable of producing this type of stuff, but I don't believe I have the aptitude and I definitely don't possess the knowledge. I am sure you enjoy sharing this skill set since most of us appreciate it, but it's also great that you are willing to share - like so many others. Thanks.

[dw1]

Man, you just saved me a buttload of work, as I was starting to engineer a system like this!

(Well, my enclosure was a different shape, but it was also "recycled" from some obsolete equipment at work.)

If you would be so kind, can you e-mail me a schematic?

Thanks much.

[ischmitz]

Sorry dw1 but I don't have a dedicated schematics of any sort. I simply whipped up a couple of waveform generators based on the ICL8038 for RPM and O2 signals and then used two 74ALS169 synchronous counters as a frequency divider to get the reference pulse derived from the engine speed pulse. I used the data sheets and some generic PCB board and soldered little wires to it. It ain't looking pretty but it works. I didn't create any documentation.

I can post a picture of the inside of the box when I get home tonight but it'll take away from the beaty of this. It looks MESSY...

Ingo

[ianc]

That is about the coolest thing I think I have ever seen. Well, almost...

So can we all send you our DME's now for test?

ianc

[KTL]

Originally Posted by ischmitz

Sorry dw1 but I don't have a dedicated schematics of any sort. I simply whipped up a couple of waveform generators based on the ICL8038 for RPM and O2 signals and then used two 74ALS169 synchronous counters as a frequency divider to get the reference pulse derived from the engine speed pulse. I used the data sheets and some generic PCB board and soldered little wires to it. It ain't looking pretty but it works.

Ingo

You make it sound like, "Meh, I just cut a few pieces of wood and screwed it together. It's a bit crude, but it works....."

Guys like Ingo that understand all that stuff are a huge benefit to those of us who don't have a clue how these things work!!! Hey, somebody's gotta know how all the electrons make magic

[GH85Carrera]

If I go to Radio Shack and ask them for a couple of waveform generators based on the ICL8038 for RPM and O2 signals and two 74ALS169 synchronous counters as a frequency divider how puzzled do you think the employees will be?

[charlesbahn]

Very cool. Another option is a break out box. With the one shown as posted below I can monitor all functions of the DME in real time in the car and while driving. Watch EBAY/craigslist for the box and cable, they come up from time to time for not much $, but you have to know what you are looking for.

DME breakout box - where can I get one?

[Joe V]

Ingo,

Do you see a cruise control brain tester in your future? ? With all the "accelerates, but won't hold speed" issues, you'd make a mint in diagnosis, and possibly repair.

[911st]

Cool.

Wish someone would come up with how to add a TPS and convert it to a MAP system like Proto. dose.

[Wavey]

Wow, nice work Ingo! If Loren was still here, he'd be having a stroke right about now.

[KTL]

Originally Posted by Wavey

If Loren was still here, he'd be having a stroke right about now.

I was thinking the same thing when typing my response.......

[nesslar]

Wow. Nice work, to say the least! It's the DME Frankentester!

[rick-l]

How did you simulate the two variable reluctance sensors?

[ischmitz]

Originally Posted by rick-l

How did you simulate the two variable reluctance sensors?

An ICL8038 with 0-20 kHz variable square wave output coupled to the inputs via small capacitors to remove the DC component for the speed sensor.

Then two 74ALS169 cascaded counters to get a reference pulse every 129 pulses. I had to play a little bit with some RC network to get a nice zero-crossing. It turns out the 3.2 DME isn't very picky for both signals.

When it comes to the 60-2 signal for the later DME it is a whole different ballgame. That DME cares about the polarity of the zero-crossing for the missing tooth signal.

Ingo

[rick-l]

Is this the way the DME ignition controller charges up the coil (the output of that differential pair and darlington)?

In THIS THREAD he says he measures 4.5 volts across the coil. Is this what he sees? 32 watts in the coil and 70 watts in the darlington with the key on engine off seems kind of high.

The arbitrary behavioral voltage source applies either 13.5 volts or the error of the current compared to 8 amps. Of course in the DME it is on the low side.

[88911coupe]

I can't even begin to comprehend what you've accomplished...I just wish I knew how to do that sort of thing.

[spencejm]

Originally Posted by GH85Carrera

If I go to Radio Shack and ask them for a couple of waveform generators based on the ICL8038 for RPM and O2 signals and two 74ALS169 synchronous counters as a frequency divider how puzzled do you think the employees will be?

I think a more "realistic" (anyone get the pun?) question would be to ask how confused they would be if you asked for a simple resistor!