D-Jet Bench Setup, Let the experimenting begin (again).... Options

[JeffBowlsby]

The wire to the center cavity of the 5-pole TPS connector goes to cavity 11 at the ECU connector.

Cavity 12 at the ECU connector is the center wire at the trigger points

[BeatNavy]

That would do it. I'll check again. Thanks Jeff!

[pbanders]

I've posted in the past about the issues with replacing the MPS with a modern electronic pressure sensor, I'll briefly summarize. It wouldn't be a simple task, because the two coils in the MPS are an integral part of the multivibrator circuit in the ECU, and also because the MPS itself is the system element that handles mixture enrichment and transition under full load conditions. Now that rebuild kits are available, it's easier to rebuild an MPS that to build an active microcontroller and sensor system to simulate its operation. If anyone disagrees and wants to prove me wrong, I'll probably the first guy to buy your new replacement system!

I thoroughly read your explanation of how the system works, and I believe trying to simulate the MPS output is overkill.
(posting your very own picture here)

(IMG:http://www.914world.com/bbs2/uploads_offsite/members.rennlist.com-10819-1448134653.1.gif)

As you explain, the MPS outputs a wave form (SC+IM bias) that 'returns to zero' in some amount of time (based on manifold pressure and temp) and controls the width of the injector pulse.

To trick the system, we don't necessarily need to simulate the MPS output exactly.
All we need to do is detect the beginning of the injection pulse (TL trigger goes low), and swing our simulated SC_IM_bias low (to below the trigger threshold = ~-0.7VDC ).

Then the simulator waits until it wants the injector pulse to end, then swing back to zero.

The fact that the simulated output does not look like the real MPS output is irrelevant.

So all the MPS simulator needs to output is a negative going square pulse that swings to below the trigger threshold, then returns to zero when the injector on duration has been reached.

So the MPS simulator output would just be a inverting opamp with a -1.0 VDC negative rail and a 0VDC positive rail.

You could even drive it with a discrete output and don't need to even mess with an analog signal.

It is entirely possible that I am missing something, but I believe it is that simple.

So the MPS simulator would have an analog input connected to a modern 0-5VDC Manifold pressure sensor, an intake air temp sensor, and an input trigger connected to the MPS input from the ECU.

It would use a lookup table to determine the desired injector pulse width.
When the MPS input pulse is detected, it just drives the MPS output to ~-1.0 VDC and holds it there until the injector pulse duration has been reached then drives the signal back to GND.
(in fact the signal could mimic the waveform in your diagram labeled 'Injection pulse duration')

The ECU will see the signal cross the threshold and end the injector pulse.

Am I close? (IMG:style_emoticons/default/blink.gif)

I've thought through the same thing, it should be possible, I lacked the skills to implement, though I've been working on that! I assume the lookup table would encompass the full-load enrichment function, too? If you can mock up a prototype I can test it on my simulator and do a direct comparison to a stock MPS.

[pbanders]

stugray, which pressure sensor are you thinking of using? I2C or 1-wire? I could also give your design a try.

[Tom]

Brad,
Did you get my PM from a day or so ago?
Tom

[stugray]

I've thought through the same thing, it should be possible, I lacked the skills to implement, though I've been working on that! I assume the lookup table would encompass the full-load enrichment function, too? If you can mock up a prototype I can test it on my simulator and do a direct comparison to a stock MPS.

You could test the theory.
Do you have an arbitrary function generator?
If you can configure it for:
Single pulse, adjustable duration squarewave.
Amplitude 1.0VDC, Offset -1.0VDC
Negative going pulse
External trigger input connected to 'TL Trigger' (input excitation signal into MPS)

Connect waveform output to MPS Output to ECU


Now test the system while varying pulse durations on the arb gen, and you should be able to control the injector pulse duration just like adjusting the vacuum on your MPS vacuum pump

stugray, which pressure sensor are you thinking of using? I2C or 1-wire? I could also give your design a try.

I just grabbed something simple off of ebay that I could actually find the datasheet for (or thought I could...)
I ended up with a Denso TN079800-3280 5V PS-30
I also found a small DC-DC converter from Digikey for the neg DC voltage.

If the experiment above with the -1.0VDC pulse works and we don't need to simulate some funky waveform, then an Op-amp wouldn't be required and we could just use an opto to pull down to the neg DC rail for the output signal.

If you really want to experiment, I could send you the MAP sensor, an arduino beetle, the DC-DC converter, some 1-wire temp sensors, and I even have some high speed optos laying around.

[pbanders]

stugray, which pressure sensor are you thinking of using? I2C or 1-wire? I could also give your design a try.

Out riding my bike and thinking - digital pressure sensor probably won't be fast enough, probably have to use an analog automotive sensor and sample it at about a 1 ms rate.

[pbanders]

I've thought through the same thing, it should be possible, I lacked the skills to implement, though I've been working on that! I assume the lookup table would encompass the full-load enrichment function, too? If you can mock up a prototype I can test it on my simulator and do a direct comparison to a stock MPS.

You could test the theory.
Do you have an arbitrary function generator?
If you can configure it for:
Single pulse, adjustable duration squarewave.
Amplitude 1.0VDC, Offset -1.0VDC
Negative going pulse
External trigger input connected to 'TL Trigger' (input excitation signal into MPS)

Connect waveform output to MPS Output to ECU


Now test the system while varying pulse durations on the arb gen, and you should be able to control the injector pulse duration just like adjusting the vacuum on your MPS vacuum pump

stugray, which pressure sensor are you thinking of using? I2C or 1-wire? I could also give your design a try.

I just grabbed something simple off of ebay that I could actually find the datasheet for (or thought I could...)
I ended up with a Denso TN079800-3280 5V PS-30
I also found a small DC-DC converter from Digikey for the neg DC voltage.

If the experiment above with the -1.0VDC pulse works and we don't need to simulate some funky waveform, then an Op-amp wouldn't be required and we could just use an opto to pull down to the neg DC rail for the output signal.

If you really want to experiment, I could send you the MAP sensor, an arduino beetle, the DC-DC converter, some 1-wire temp sensors, and I even have some high speed optos laying around.

If you send the stuff to me, I can't tell you when I'd get around to it. You'd be better off doing it and I could test it out if you want, unless you have everything you need to verify it. re: Denso sensor - yeah, that's what's needed. As for the proof of concept, I don't have an arbitrary function generator but could probably do a circuit with a 555 or two that could do the function you describe.

What sampling rate does the megasquirt use? I'm figuring this would need to be about on the same order.

[pbanders]

Brad,
Did you get my PM from a day or so ago?
Tom

Will check, just got back on here today.

[stugray]

Out riding my bike and thinking - digital pressure sensor probably won't be fast enough, probably have to use an analog automotive sensor and sample it at about a 1 ms rate.

I don't think we would need to sample the MPS and the air intake temp that fast, maybe 10 Hz?
Then throw in some digital filtering (average) in software and you would have less than a few tenths of a second latency.
I'd have to play with the MAP and an oscope on a real engine to know how fast it even responds.

You wouldn't even sample the input trigger, it would operate on a input channel event trigger (arduino attachInterrupt()).
So every time the subroutine is called by the input trigger (TL goes low) it:
drives the SC_IM_bias output signal to -1.0V. (or some negative voltage TBD by experiment).
latch a system time (start_of_pulse)
Read the time averaged MAP value (MAP)
Read the time averaged Input temp sensor reading (IAT)
Using those two values, lookup a pulsewidth from a lookup table (pulsew)

set the timer in the future for start_of_pulse + pulsew
exit from interrupt routine

When the timer goes off:
drive signal SC_IM_bias output signal to 0.0V
ECU stops the injector pulse.

This subroutine would run every time the TL input signal goes low

In the "downtime" between the subroutine running, it would collect & average the MAP & Temp sensor data.

If you send the stuff to me, I can't tell you when I'd get around to it. You'd be better off doing it and I could test it out if you want, unless you have everything you need to verify it. re: Denso sensor - yeah, that's what's needed. As for the proof of concept, I don't have an arbitrary function generator but could probably do a circuit with a 555 or two that could do the function you describe.

What sampling rate does the megasquirt use? I'm figuring this would need to be about on the same order.

You absolutely could do this as proof of concept with a 555 in monostable mode.
Hookup a +/-5VDC power supply and use the 555 to drive a opto/mosfet to pull the test signal up & down

[worn]

Brad,
Did you get my PM from a day or so ago?
Tom

Will check, just got back on here today.

Well, as I live and breathe you are one of my heroes! I am still chasing my Raby sort of webcam 73, and your work has been essential to me.
Thanks for all you have done.

[pbanders]

stugray, thanks, will let you know when I get to doing the POC. Resurrecting all the stuff I did on this 5-10 years ago is going to take me some time.