We don't merely need inversion, we need the circuit to be off when the CPU is off.

When the CPU is inactive, its output pins are hi-z. A PNP won't conduct unless it's got negative base current, and that won't happen with the CPU tri-stated.



It'd be nice if Grace Park had been waiting in my hotel room when I got back from dinner.

Didn't happen.

So why can't you use a PNP instead of the NPN that drives the diode?

Oh, and sorry, if I'd known you were into her, I wouldn't have gone there. I'm sure she's looking for a shoulder to cry on since I haven't returned her calls....

Fucking hell. My 460s would give the pop on start up once every 2 weeks, but the RC750s are doing it every time the car sits overnight. I need to do this now. -.-

Show me a schematic of what you have in mind. I may just be mis-understanding what you're saying.

In regard to using a PNP instead of the NPN transistor in the original circuit. Can't we connect the output of the CPU to the base of a PNP with its collector connected to ground and the emitter connected to the -ve side of the LED. Then if we bias the base to the ground with a resistor we should be able to drive the transistor to conduct when the output from the CPU is low/floating. The output to the ignitior should then follow the output from the CPU.

I couldn't find a tool to draw circuits on my mac, hence the wordy description of the circuit.

Disclaimer: I am not an electronics expert so pardon me if this is wrong or stupid.

My name's Joe, and I'm a PC. We've got an app for that. :D

Seriously, I think this is what you & Abe are describing:

http://img29.picoodle.com/img/img29/...Pm_7db9d9b.png

The reason I've had concerns here is that you need a small enough resistance to reliably turn on the transistor when the CPU is in la-la land, yet as the value of R goes down, the current which the MS is pissing away out of PTC0 / PTC2 to ground (when on) goes up. I've just been too damn lazy to look up the minimum IB needed to drive the ZTX553, which I'd assumed to be quite high, given its max IC of 1A (and the fact that PNPs usually suck in this regard). Having done so just now, I see that it is in the μA range.

Might work. Try it and find out. Take your pick- desolder a pair of transistors, clean out the holes, and replace them with two other transistors and a couple of tacked-on resistors, or add two additional transistors and resistors in the proto area.

What program do you use PC?

That's the circuit I am talking about.
Can you calculate the resistor values please?

I am still building my MS2 for my 91.
I am in the process of trying to figure out all the different mods I want and how to assemble them.
I will try the PNP circuit while I assemble the spark output circuit.

Thanks.

Eagle CAD will run on Mac, Linux, and Winblows:

CadSoft Online: Download

If the CPU output is 0-5V, then 470 ohms for the upper right hand (pullup) resistor is plenty, and 4.7k-10k for the base to ground resistor will be fine. The leftmost horizontal resistor is unnecessary.

Just about any TO-92 PNP will work, such as the 2N2905 or the 2N5551.

I use the free schematic editor that comes with the ExpressPCB package, for which Abe criticizes me on the grounds that Eagle is better.

The leftmost horizontal resistor is part of the standard 3.0 layout. It's R26 / R29 on page 7 (R3.0).

Bear in mind that the lower the better for the +5 pullup, since it dictates the current available to drive the igniters which as we've shown from past experience, are hugely capacitive. 220/330 is preferred here, as little as 100 is really ideal when you're dealing with a 2222 or similar.

The Toyota and Nissan COPs I tested didn't have capacitive loady inputs. I've posted how much current they require in the big COP thread.

I didn't create this mod only for people with COPs.

In my personal opinion, the NPN design is more robust, and not significantly more complex.

Without thinking it out, basically, yeah - stuffing the different part in the same hole. Of course, a small, surface mount resistor would comfortably attach to the bottom of the board to pick up both pins, so no wires to run.

Well, the idea is for fresh builds, if it's put this part in instead of another, ok. You're right, tearing apart an existing board is more work and slightly risky (lifted pads, etc)


Actually, I've been using KiCAD - reminds me a lot of orcad. Eagle has really annoying limitations. And it's cross platform, so you can share with weird open-source/linux people. Maybe it works on mac? I dunno. Anyway - one package all the way through fab, why not?


Seriously, it's all about COPS, they are such a joy to work with. Everyone should buy them next time they need cables, costs about the same and you're set for life.

This, from the man who failed to implement this freely available design on his NB PnP board (and who still hasn't paid me any fucking royalties on the A/C circuit that he stole)

I never have issues with 'premature ignition' in my car. Maybe you should speak with a doctor about it?

Since my car is not driving anyway, I've decided to go ahead and order the parts I need for this mod.

2x 2N2222 TO18

Data sheet:
http://www2.produktinfo.conrad.com/d...219_2N2222.pdf

I've expaneded the write up from Matt. This is correct right?

Looks good...

Oh? Whose igniters have super capacitive inputs? Miatas?

Explain please?
Does this mean remove the two red wires below the surface of the board? Ex. PAD1 and IACB2B en PAD3 and X ?