D16 Shift Light

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Rick Finsta
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D16 Shift Light

Post by Rick Finsta »

I'm looking to run an Autometer 5330/5331 shift light off of D16. Will I need to replace the Q8 transistor with a ZTX450-ND to get a little more current capacity? If I am reading the data sheet right on the 2N3904FS-ND it is only good to 0.2A (though I have read several sources saying that the circuit is good to 0.5A) whereas the extra ZTX450-ND I've got from Q4 should be good for 1A? I can't imagine the shift light is going to draw more than that...

Or am I better off just using it to drive a relay that turns the light on in its stock form by taking the top of R29 out of SPR4 to ground a relay (since the 30A Bosch units need <0.2A to close the contacts)? If I do that, is it like the Spark A output I'm using off of the top of R26 where you just leave the rest of the LED circuit in place?

This seems really rudimentary but I've been digging through the documents and my notes for some time now and I'm seeing several ways to skin this particular cat.
Rick Finsta
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Re: D16 Shift Light

Post by Rick Finsta »

Okay so I stuck the ZTX450-ND into Q8 and ran the top of R29 to SPR3. I get 5V at the DB37 SPR3 now when I want it. Should I just do an external pullup or should I wire the 12V pullup into the proto board?
Rick Finsta
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Re: D16 Shift Light

Post by Rick Finsta »

Okay better question. Would it be easier to just use the new transistor to ground the shift light? If so which pin of the new Q8 would I run to SPR3 so I can turn on the shift light by grounding it through MS? Now that I think of it that's the easier way, correct?
Rick Finsta
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Re: D16 Shift Light

Post by Rick Finsta »

I feel like a retard with electronics. Okay, how about I remove R28, and run 12V+ from the banded side of D9 through a 1-10k resistor (start with 10k) to the D16 side where R28 was, where I'll also connect out to SPR3, which should send 12V signal out SPR3 when D16 lights? Or do I need to replace D16 with something like an 1N4001?
Rick Finsta
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Re: D16 Shift Light

Post by Rick Finsta »

Will this work?

Image

Anyone?
Matt Cramer
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Re: D16 Shift Light

Post by Matt Cramer »

That will work without removing any resistors.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
Rick Finsta
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Re: D16 Shift Light

Post by Rick Finsta »

Thanks a lot for the reply, Matt.

Don't I want to disconnect D16 from 5V? The only way I could figure to get the 12V to D16 through a resistor was by removing R28 and putting a resistor in line from 12V to the D16 side of where R28 is on a stock 3.0 board. Otherwise do I just leave it hooked to 5V and the D16 LED just won't light anymore (it will just function to keep the 12V flowing back into the 5V header when the circuit is activated)?
Six_Shooter
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Re: D16 Shift Light

Post by Six_Shooter »

D16 will function as a shift light then. It's an active low circuit, so when the shift light is commanded, the LED will also turn on.
Tha Toy: 1973 Datsun 240Z Turbocharged, and loads of fun, now MS'd
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Rick Finsta
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Re: D16 Shift Light

Post by Rick Finsta »

But if there is 12V on the Q8 side of D16, how would 5V flow through D16 to ground through Q8? Wouldn't there be a negative potential there? I think I'm just going to hook up the Cathode side of D16 to SPR3 and use that to ground the shift light and not worry about whether D16 still lights or not. It doesn't really matter other than to my OCD brain.

Thanks for the help - maybe a dumb question but I learned how to recognize a grounding transistor circuit at least.
Six_Shooter
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Re: D16 Shift Light

Post by Six_Shooter »

No. Think of Q8 as a switch here, simple on/off. Once it turns "on", then ground is connected through Q8 to the LED and the shift light (relay). Q8 simply grounds those two points.

I can see why you'd think the potential is different, but the load(s) is where the voltage drop happens, in this case the shift light relay coil will drop very nearly the full 12V (there's a slight drop across CE of the transistor, but small enough to be ignored in this case), and the combination of R28 and D16 is the other load. Each node has its own potential and do not effect each other in this circuit.
Tha Toy: 1973 Datsun 240Z Turbocharged, and loads of fun, now MS'd
Tha Otha Toy: 1923 T-bucket Hot Rod, Currently Sniper'd
Tha Daily: 2005 Chevy Blazer
Tha Summer Daily: 1987 Buick Skyhawk hatchback
Tha Long Term Project: 1985 GMC S-10 Jimmy, hasn't been fun for a while
Rick Finsta
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Re: D16 Shift Light

Post by Rick Finsta »

LOL well in any case the shift light works. Thanks again for the help on this - I have a lot of trouble with circuits.

I took the opportunity to install a MapDaddy and upgrade the DB37 socket on the board since my case had been apart so many times I'd stripped the stamped sheet metal threads on the old one. The new ones come with the nice thick nuts on the backside. I also upgraded to thumb screws now that I'll likely not have the ECU out for awhile...
Rick Finsta
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Re: D16 Shift Light

Post by Rick Finsta »

Incidentally I got this hooked up in the car and it didn't work anymore...

...because the Shift Light is also an LED and therefore directional. LOL

I swapped leads and it works great now. So in conclusion, I replaced Q8 with a ZTX450 and then connected the Cathode of D16 to SPR3 and then out to the shift light, which is getting 12V+ supply when the fuel pump is energized.
Rick Finsta
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Re: D16 Shift Light

Post by Rick Finsta »

I just fired the car after converting to MS3+3X and now my shift light seems to randomly activate, and if I kill the ECU when it is happening the light stays on. This never happened on the MS2. Should I look for a short to ground somewhere or is there something in how I wired this that could cause that issue? Maybe if voltage drops below a certain point it is acting like the alternator charge light does where the potential difference is enough for current flow?

Ya got me, but I do need to fix it. Nothing in my tune that would cause this I already checked all that so it is either the modification or a ground short somewhere...
Rick Finsta
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Re: D16 Shift Light

Post by Rick Finsta »

Alright the light seems to be flickering on when AE is triggered... what do I have to do to stop the MS from trying to use D16 as an AE trigger indicator?
Rick Finsta
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Re: D16 Shift Light

Post by Rick Finsta »

Ha! I'm an idiot. I had D15 set as the output. I got confused about which I had hooked up because I remembered issues with different manuals referring to D15/D16 as WUE/AE incorrectly. :RTFM: :RTFM: :RTFM: :RTFM: :RTFM: :mrgreen:
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