MicroSquirt.com read only forum (Jan.15,2018)

Hi all,

I'm planning a MS + EDIS system, and I've been studying the V3 schematics. I understand the convenience of a one-size-fits-all approach for the TACH input, but for myself the VR system looks overly complex for the PIP signal from EDIS. And I'm a tinkerer at heart, so I wanted to try something new.

My idea is to just use a simple 2N3904 grounded emitter stage. Basically it would be the same as the V3 LED indicator circuits (e.g., Q6 and friends), with the input coming from PIP and the output taken from the collector. The only changes would be :

a) Replace the series input resistor (c.f. R26) with two 500 ohm resistors in series; where they join add a cap to ground to filter crud from the input.

b) Add a zener diode for protection.

Anyway, I feel pretty sure I can make this all work fine on the bench, but I'm concerned about the unforseen gremlins that live under the hood. Are there any traps I've overlooked ? Is the PIP signal fairly clean and well-behaved ?

TIA

That ought to work ok. If you do that you can omit all of the opto and VR components (as I'm sure you've figured already)

EDIT: This will work ok on MS2, but provides the wrong polarity for MS1.

James

Wow, thanks for the speedy reply. I just figured out how to get my ideas into an image. FWIW, here's what I was trying to describe :

(hope this works ...)