pcmhacking.net

I am looking into suitable optical interrupters but only one which is the style I used in my VP is this one from RS. Its a darlington type though. That just amplifies the output right?
This is a vertical slot, all others are horizontal which wont fit in the tiny space if I had to make a 90º bracket for it.

http://australia.rs-online.com/web/p/sl ... s/6666508/

Done-diddly-done.
Screenshot is also in zip file.

oh yeah, btw that 560R on the relay contacts is not suppose to be there. it was initially for a resistor that is used for the cruise control (- set) signal line. Since its just going to the cut out line its just a straight switch on the brake pedal. I will be wiring in parallel with that. Yeah excuse my schematic. The final circuit was changed a little with some improvements. I recall a polarity safety diode before the 7812 too but I am thinking with 13.8 then 0.6 drop over the diode there is only 13.2 ish before the 12v reg so thats no much. I am not sure what the min input should be for a 7812?

For car stuff I use a series 10R 2 watt resistor feeding a 470uF cap and 1 watt zener diode across it to protect stuff from transients. Never ever had a failure. With the 7812 there you must have been lucky.

i don't know how it even works. I must of used a lower voltage red, coz even a low dropout 12V reg doesn't have enough head room on 13.8. I maybe using 7809 ?

the 4093 can operate all the way to 15v but obviously much lower as well.

Righto, have a look at this.
I ditched the 12V reg and replaced it with a 10R 2W surge rated resistor, 470uF and 16 V 1W zener. Bulletproof.
All relay contacts are now available.
The 10R 2W has an element 14 part number.
The 1W zener is available from Jaycar.
Sensor pcb done also.

Sweet! thanks heaps.

Do you have the schematic for the relay board? I just want to make sure value of some of the resistors are correct as this how be running at car system voltage without the reg. And the 16v zener clamps it at max 16v in a surge condition?

I did it without a schematic but could soon chuck one together. What might be a good idea also is if you trace it out yourself, because I am more likely to draw up what it is *supposed* to be... but if you do it independently you can be more certain that it is right.

The zener will clamp at more or less 16 volts, depending on how far *continuously* overvoltage you go. In an automotive environment you are most likely to get very short duration transients and the 10R and 470uF take care of these. 99.9% of the time the 16V zener is not going to conduct at all. It would be at max dissipation if the input voltage was continuously at 17.6 volts. Continuous overvoltage situations are very rare.

Watch out for the possible reverse polarity current. Adding a diode will fix that and also let the 470uf cap work properly. A 16V zener also allows the logic IC to be operated extremely close to its absolute voltage ratings in an over volt situation, 15V is its max normal operating voltage.

So a 15V zener would be ok? its getting close to system voltage though.

Its kinda why I was thinking 9v reg would be good. I never intended the reg for protection, just for keeping stable voltage for the sensor and IC. Extra protection in front of the reg would be ideal imho