reverse engineering-copying

[kinarfi]

I've had this switch on my dash and finally decided to see how it works, but need some other opinions besides my own. Attached is what I came up with, but it won't sim properly. Mainly, what do you think Q2 & Q3 are?

 

[ronv]

What does it do? Just light the LEDs?
My guess is that Q1 & Q2 make a latch set by the brown switch and reset by the FET.

 

[kinarfi]

it is the on - off switch for the Audiovox after market cruise control that I started off with a year or two ago, on powers the system up and off shuts it down. Set and resume are self explanatory and if the system is operating, set accelerates and resume coasts.
I can see how closing the brown contact gets things running, but how does the stop contact make it stop, my first thoughts were that it shorted base to emitter and caused it to shut down similar to turning off and SCR. Any one else have any ideas?
Kinarfi

 

[ronv]

You got it.
Q1 is off, Brn switch puts a + on the base turning on Q2. Q2 drives the base of Q1 negitive holding it on. M1 shorts out the base to emitter of Q1 turning it off.

 

[kinarfi]

OK! but it won't sim, either spice can't handle the logic or I need to choose a different fet for the sim, thanks.

 

[ronv]

Take a look at the changes around the reset switch and see if maybe it is wired that way.

 

[kinarfi]

Looks the same as my drawing and mine is simming just fine, now that I made a few changes. This is a circuit I'll have to remember for when I want a high current SCR