Electronics > Beginners

Traffic light circuit with 556 timer?

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phennessey:
I don’t have any EDA software (yet). I plan on getting a copy of Fritzing soon.

SmokeyTheElectrician:

--- Quote from: james_s on December 22, 2019, 06:59:26 pm ---... As I mentioned earlier, this is an unusual way of doing a traffic light.

--- End quote ---
Yeah,
I mostly agree,
but I would bet a pack of Big League Chew
  ( and  as a matter of trivia of sorts )
that at least some of the first traffic light circuits
had more in common with the OP's original schematic
than most of what was given as advice ( that is not
to say there was anything wrong with any of that
advice, quite the contrary, you all totally pointed the OP
in the right direction for when they become interested
in tackling more complex circuit applications).

In those original traffic lights I am thinking of,
you'd likely find pneumatic delay relays functioning
as the timer elements in a string of one shots connected
in a ring (think of a ladder logic implementation).

cheers
&&&
Merry Christmas to everybody

schmitt trigger:
Back in the early 70s, I worked for a summer for the city’s traffic light department, in maintenance.

There were a couple of systems, that I remember:
-Relay ladder logic as you described.
-A camshaft driven by a 1RPM geared synchronous motor.

james_s:
There's lots of information out there about traffic light controllers, at least the stuff used in the US. Eagle, Econolite and Crouse-Hinds were some of the big makers here. Early systems used motor driven timing wheels and solenoids, then in the early 80s microprocessor based controllers started taking over.

https://northstarhighways.wordpress.com/2016/09/10/how-traffic-signal-controllers-work-part-1-an-overview-of-controllers/

Ed.Kloonk:

--- Quote from: schmitt trigger on December 21, 2019, 06:15:45 pm ---Traffic lights are classic classroom example when learning about state diagrams and/or truth tables.
I have made a fictional intersection in a pair of streets: Second avenue and Main street. Please check the attached Excel spreadsheet.

To keep things simple, I've arbitrarily made them one way, and have not included turn signals.

The circuit has four states, which repeat endlessly and six outputs, one each for each light color on a street.
Fortunately, four states can be realized with a two bit counter, with a single IC dual flip flop like the CD4013.
 
Then using sums of minterms, you decode each output. For instance, the Second ave green light is simply A * B/

The fact that the yellow light has a different duration than the other lights complicates things a little, but with additional steering logic you could change your astable's time constant.

Of course, doing this with a microcontroller is trivial.

--- End quote ---

Part of the enjoyment of visiting England and driving around there is that country's feature of the traffic lights facing you goes amber/orange prior to turning green. This gives the motorist time to extract a finger and put the vehicle in gear.

Returning home, it's always a disappointment that we cannot implement such an innovation here. I once asked someone who works in the transport ministry why we can't manage it? A blank, short-circuited look for a few seconds and then the response: "Oh, cost."

 :palm:

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