Beginner needs circuit design help for 555 timer project

Thread Starter

RigidCollision

Joined Dec 10, 2018
8
Hi Guys,
I am embarking on a new project to design a circuit for an automatic vehicle signal actuator.

The goal of the project is this:
The problem.
I have a car that has indicators operating on a standard 12v on-off-on toggle switch. As you can imagine this switch gets left on occasionally. Both misleading and potentially dangerous.
The solution
Replace the toggle switch with a 2 way momentary switch and create a circuit that supplies 12v to the correct circuit for 5 seconds. In addition, the timer is continually reset when 12v feed from the brake circuit is applied. As soon as the brake this feed stops, the 5 seconds starts again.

Effectively, this allows a a lane changing signal as well as a solution for waiting at junctions or to cross a stream of traffic.

I would imagine a 555 timer would be the way to start with this (or a 556 dual timer).

From what I can tell I need to use 'Monostable' mode.

Where do I go from here!?
Is the 555 (556) the right choice?
Is it a robust solution?
 
Last edited:

Alec_t

Joined Sep 17, 2013
11,414
Before you start on this project, have you checked that modifying the car's electrics in this way is both legal and insurer-approved where you live?
 

Thread Starter

RigidCollision

Joined Dec 10, 2018
8
Before you start on this project, have you checked that modifying the car's electrics in this way is both legal and insurer-approved where you live?
Yeah, we're cool. :)
As you can imagine, a car with a toggle switch indicator system is not a standard thing anyway.
 

brezel1111

Joined Dec 19, 2018
3
You could divide the brake signal to ttl level and lead it to the reset pin. You'd have a pullup/puldown resistor depending on high active/low active brake signal. This way you would have one timer for the blinking - astable - and a timer set for 5 sec or whatever you want - monostable. There might be a better way but I this way you would need 4 555 timers: 2 for left and 2 for right.
The monostable will enable the astable timer.
 

Thread Starter

RigidCollision

Joined Dec 10, 2018
8
Hi, Thanks for the diagram.
I was going to use a 556 (effectively a doubled up 555 timer) and inject the new circuit to 'hijack' the current toggle switch and provide a power feed to the existing blinker in the wiring loom. I would also imagine that the sensible thing would be to use a couple of relays to handle the vehicle current?
 
I would also imagine that the sensible thing would be to use a couple of relays to handle the vehicle current?
If you hijack the toggle switch, you dont need the astable timer or realys - mosfet might be better here anyway. There are many many ways to go for it, you just have to make up your mind: )
 
Last edited:

Thread Starter

RigidCollision

Joined Dec 10, 2018
8
I assumed a 555 timer was the only real solution, so any advice is always appreciated. The MOSFET is a real simple solution but I am concerned about heat. Any other options?
 
Top