simple traffic light controller

[jabboo]

hello,
I need I want to build a traffic light controller
ive looked around on the internet and cant find any suitable schematics
ive found this product though
http://www.trafficlights.com/P3ad.htm
if you have a look at the picture of the controller on that board it looks
relatively simple
like a 555 timer or something like that with a bunch of resistors ?

would anyone have any idea how they did it ?
or where I could find a schematic to do something similar to that ?

green for 35seconds
amber for 5 seconds
red for 20 seconds
or something along those lines

I don't need the option of flashing caution mode so that rules out the
switch.

any ideas ?

 

[Ken Taylor]

hello,
I need I want to build a traffic light controller
ive looked around on the internet and cant find any suitable schematics
ive found this product though
http://www.trafficlights.com/P3ad.htm
if you have a look at the picture of the controller on that board it looks
relatively simple
like a 555 timer or something like that with a bunch of resistors ?

would anyone have any idea how they did it ?
or where I could find a schematic to do something similar to that ?

green for 35seconds
amber for 5 seconds
red for 20 seconds
or something along those lines

I don't need the option of flashing caution mode so that rules out the
switch.

any ideas ?

It's probably a 556 (dual 555). However you should use a decent search
engine, there's heaps out there if you search on +"traffic light controller"
+circuit

The 555 is certainly popular for this, but if you want to control several
light sets at a time (as in a real intersection) you probably should go for
some programmable logic, as in a PIC or a micro. What does the lab note tell
you to do?

Ken

 

[jabboo]

hi ken
this is not for a lab nor an assignment
just for my own personal experience
its only a single traffic light nothing complex
doesn't have to interface with anything just flash in sequence.

I think im going to go for a 555 timer connected to a 4017 decade counter

connected like this
out1 - green
out2 - green
out3 - green
out4 - green
out5 - green
out6 - green
out7 - amber
out8 - red
out9 - red
out10 - red

and have a 555 timer set for 7 seconds
effectively giving me
42 seconds for green
7 seconds for amber
21 seconds for red

a question now
anyone see any flaws in this ?
and how easy is it to set a 555 timer to 7 seconds ?

 

[James]

I have a circuit laying around somewhere that I designed years ago for
realistic control of an intersection with adjustable phase times & "green
extension" time (time taken for vehicles to clear the intersection between
the adjacent green phase), and all done using 4000 series ICs...it was a
real pain in the ass! Much easier to write a few lines of code for a PIC or
similar to perform the same task.

Running only one "traffic light" the easiest and cheapest way for sure would
be to use a 555 & a decade counter.

Do you want to control "real" traffic lights or just LEDs etc? Noticed that
the circuits obtained from a web search use triacs to switch mains
voltage....not needed for traffic lights in aus, they operate at low
voltage, typically rated at 10vAC for incandescent & 12V for LED arrays
(have built in switching regs).

James

 

[Ken Taylor]

hi james

i think they are real traffic lights ? im not sure i get them tommorrow, but
i would like to try and get them to run off 12vDC, so i was thinking of
using halegon downlights ? anyone care to comment?
im not sure
they looked like real traffic lights.
know of a cheap way to convert them to 12vdc? or something low voltage. i
think they are 240v globes in them if i remember correctly. so id have to
replace them.

One of the first sites I found with a Altavista search used three 555's [
deluxe version! ] to run a set of LED's.
http://etakappanu.eng.buffalo.edu/trafficlight/TLC.html
There were a number of university sites which used the example of a traffic
light controller for showing how state machines work.

There were another couple of sites I found last night with single-555
circuits, but oddly enough I can't find them from this PC even though I'm
using the same flavour Altavista search engine. Hmmmm......

Cheers.

Ken

 

[Ken Taylor]

Did you find those sites with the 555 circuits?

Ken

 

[jabboo]

hi ken
yes, thankyou for the site you posted, was an interesting read.
ive searched on google turning put quite a few sites but that one didn't
come up?

I went out this morning and bought the parts I needed.
and ive read through some sites about how to use 555 timers
so now im off to give it a try on a breadboard to see if I can make it work
if indeed it does work then ill put together a more permanent circuit.

 

[Rudolf Ladyzhenskii]

I actually had to do traffic light as an assignment in the Uni, so I
automatically assume this.
Sorry, if I offended you.

The one I built in Uni was a bunch of flip flops (a big bunch!). Basically,
an exersise in building a state machine.

I would really suggest using a microcontroller. The result would be a simple
(less chips) solution, while quite flexible. Any changes can be integrated
with a firmware upgrade.

If you want to use 555 timer, you will need few of them (one for each time
intervale) with some logic around it to make it work.
Or you can use a single timer to generate, say 1s interval and use counters
and flip-flops to create a state machine responsible for the controlelr
behavour. In any case, I beleive, it would be more complex than using a
micro.

At some stage, Motorola was selling 68HC705JA1 kit for about $50A. Something
like that is all you need. And it had nice books with it too. Other
inexpensive (in terms of development cost) chips would be Zilog Z8 and TI
MSP430. All have nice easy-to-understand literature and plenty of examples.
With micro, all you will need is a micro itself, crystal (in case of TI you
can run without one), power supply and interface circuit to run the lights.

Rudolf

 

[Jabboo]

hi KLR
thanks for your reply
to be honest i wouldnt have a clue how to use a pic nor how to program it..
ill just stick to this simpler version since its more suited to my level of
knmowledge
but im always open to learning.

i will however take into consideration your idea about switching on extra
resistors to the 555 with the output pins.

thanks for your feedback, greatly appreciated

 

[Jabboo]

hi james

i think they are real traffic lights ? im not sure i get them tommorrow, but
i would like to try and get them to run off 12vDC, so i was thinking of
using halegon downlights ? anyone care to comment?
im not sure
they looked like real traffic lights.
know of a cheap way to convert them to 12vdc? or something low voltage. i
think they are 240v globes in them if i remember correctly. so id have to
replace them.

 

[David Sauer]

I actually had to do traffic light as an assignment in the Uni, so I
automatically assume this.
Sorry, if I offended you.

The one I built in Uni was a bunch of flip flops (a big bunch!). Basically,
an exersise in building a state machine.

I would really suggest using a microcontroller. The result would be a simple
(less chips) solution, while quite flexible. Any changes can be integrated
with a firmware upgrade.

I've made one with a PLC with input detection, when one input went
active and had red it would swap the lights over to green.

Then you have to re-program in the event that two cars arrive at
opposing lights at the same time they don't swap over immediately, but
wait a few seconds for the car with green to pass before swapping
over.

Once you get the whole thing going, then try and reprogram the thing
so that the thing is fail-safe, as in that it's impossible for both
lights to have green at the same time, which if it does happen should
trigger a watchdog and flash the lights amber until manually reset.

PLC/PIC same thing really. PICs are lots cheaper.

 

[Matteo]

On Tue, 1 Jul 2003 12:35:48 +1000, "Rudolf Ladyzhenskii"
I've made one with a PLC with input detection, when one input went
active and had red it would swap the lights over to green.

Then you have to re-program in the event that two cars arrive at
opposing lights at the same time they don't swap over immediately, but
wait a few seconds for the car with green to pass before swapping
over.

Once you get the whole thing going, then try and reprogram the thing
so that the thing is fail-safe, as in that it's impossible for both
lights to have green at the same time, which if it does happen should
trigger a watchdog and flash the lights amber until manually reset.

basically what i had is the lights going in sequence, with 5s delay
inbetween each change, just to see it working

eg:

NS - GREEN / EW - RED
NS - AMBER / EW - RED
NS - RED / EW - GREEN
NS - RED / EW - AMBER

then restart the sequence
the input detection for the cars would keep which ever intersection NS
or EW green for another 5 seconds, plus the 5s delay between each
sequence

so this way it is impossible for the lights to be green at the same
time, i was going to program in a timer to basically see if there was no
traffic detected for a certain amount of time, then it would just freeze
the sequence until there was traffic at an intersection