Speed Control-Traffic light

Thread Starter


Joined Jul 25, 2007
I am thinking about implementing an automatic electric car speed controller

when it sense a the light of a traffic light signal. this implies that when the car

is at a distance from a traffic light emits Red it should start to decelerate and

stop a minimal distance from the traffic light and if the light goes to green it

should re-accelerate. Can this be implemented without the help of

micro controller, if yes can you suggest how?;)


Joined Jan 10, 2007
Im not good at electronics at all but if I've had to do this, i would use a kind of phototransistor filtered to only see red and when it sees red it activate a dimmer or something to de-acelerate the motor. Then other phototransistor but green filtered and it will re-activate the dimmer.
I really dont know how to do this, but this is my opinion.
But i'm not sure if they are filtered phototransistors to red or green.



Joined Apr 20, 2004
For an individual car, this is probably just possible to do. Practical problems are things like detecting the traffic light against full sunlight or in the presence of conflicting illumination sources. Not all traffic lamps are alike. Placements are not standard, nor are they all using the same lamps/LED's.

There is an outfit called TAOS that makes cheap light to voltage converters. They are sensitive from IR up to UV. Much better than phototransistors. Now all you have to do is figure out if the traffic lights are overhead, or corner post mounted.


Joined Aug 15, 2007
I fear you'll need to deal with a lot more variables: the gross weight of the vehicle, the stopping power of the brakes, maximum comfortable decelleration (don't want the passengers to go through the windshield!), velocity of the vehicle, distance to the intersection, and other vehicles also stopped at the light.

And what will happen if the light turns red when you are too close to the intersection to stop outside of it? An amber-light detector may work, but there are sodium strret lamps of the same hue as the amber traffic lights! <grrr!> You will also need to filter out cars' and trucks' tail lights as well as decide which is the "correct" light when (a) there is more than one light at an intersection, or (b) there is a light at several intersections, each a block apart, or (c) the light is out, or any combination thereof.

Also, what if there is a stong wind and the light is swinging, only showing red (or green) sporadically? In such a case, humans know that the hidden red light has not turned off, but will a simple detector?

(Gee, drivers deal with a LOT of information, don't they?)

So, in response to your question, "Can this be implemented without the help of [a] micro controller," I would say I'm not sure it could be implemented without a number of microcontrollers!