attiny in car delay then send a 12v pulse

Using Arduino General Electronics
#1

I am trying to put together something that will work at 12~13vdc (car battery) that when the key is turned, and it gets 12v, that it waits 3~4 seconds (timing is not all that critical) then sends a 12v pulse (maybe 500ms). I think it is a logic pulse and 20ma should be enough.

I have tried a 555 but after the delay it is a solid signal, and that isn't what I need, I guess I can use a 556 one timer is delay and other is trigger, but I would rather use an ATTiny, so I figured I can:

use a 78L05 to get 5V use an ATTiny85 with a wait for 3~4 seconds (or whatever I need to tweak it for the clock speed) then set the pin high or low for .5 seconds.

I have tried sending a 5v signal and that doesn't work, it needs to be closer to 12v.

But I guess I need to use some sort of relay for the 12v signal? I would rather not use a relay as it will be too big for the packaging I want to do. This is for a couple of applications, like turning off the sound on a Nissan Leaf and disabling traction control (both of which default to on every time, and always feeding a trigger to them do not disable and set faults).

#2

An attiny makes it too easy :)

Use a resistor divider to split the 12v signal to say 4v for a logic high, when you see it, delay (4000); then digitalwrite to a transistor to send the 12v signal back...

#3

Use an NPN transistor? I can put 12v on the emitter and get 12v on the collector? I thought I could only do ground on the emitter and get ground on the collector.

#4

bangster: Use an NPN transistor? I can put 12v on the emitter and get 12v on the collector? I thought I could only do ground on the emitter and get ground on the collector.

You need PNP if you're going to connect it to the 12V side.

#5