Hi all,
Hoping I could get a little assistance. I'm trying to design what I’d expect to be a pretty simple circuit, but as this is my first one ive tried to custom design I'm struggling a little. I know the basics of electronics, but the last time I used a 555 timer was in high school!
What I'm trying to do, is design a circuit which can handle 12-14v (for use in a car), can take a specific input signal (like seeing 12v on a particular pin) and then latch a relay. The relay latch time needs be variable and set by a potentiometer, time range between 0.5 and like....3-4 seconds would be fine.
The circuit should only perform this action once each time it sees the 12v input signal.
My initial thought was a 555 timer, for which I've built the following (probably horrifically wrong) circuit using various examples of tutorials ive found.
![](https://photos.smugmug.com/General-Images/i-RHHc9hq/0/2f043ea2/M/Capture3-M.png)
My issue is (aside from the fact this likely is wrong) is that I need it to latch the relay once, then ignore the command until the 12v signal goes away again, wait for say 5 seconds, and then be ready to listen and perform the action again, I don’t think a 555 timer can do this (just run the instruction set once basically).
I'm aware such a thing is possible to do with an Arduino and a relay PCB, but this isn't desirable as I want a low cost of parts (I don't see the point running a microcontroller like an arduino, when I need fairly simple actions) and also because I want to design a PCB for it all, not have various modules dotted around linked together with jumper wires.
TO make it simpler, what im actually trying to do, is detect when my car is put into reverse, then dip the electronic side mirror for X amount od seconds to aid in paralel parking.
The module needs to ignore the second “Dip” command as theoretically if you kept putting the car in reverse quickly, you could run out of travel on the motor.
Also, as the mirrors are electronically controlled, it would need a way for me to splice in thje existing mirror wiring to allow the OEM controls to still work. There are modules that do this (and are wired up like the below), but the asking price is too hign for something so simple, and it would be fun to build my own!
![](https://photos.smugmug.com/General-Images/i-5MLJB7j/0/5522007f/M/Capture2-M.png)
Any help is appreciated
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/xsmiley.gif.pagespeed.ic.R8GFI-pF6f.png)