How to Design a Traffic Light with a DC Power Supply

[Shahil]

Hi guys!

I need to design and build a traffic light with an accompanying DC power supply. The DC power supply must be a 5V source obtained from a 240V AC (50 Hz) mains source with a short circuit current of 200mA. This will be used to drive a digital logic circuit controlling the traffic lights.

The traffic light intersection is a 4-way intersection with timings as follows

Daytime
N-S
Red 16 sec
Green 12 sec
Amber 04 sec
W-E
Green 12 sec
Amber 04 sec
Red 16 sec

Nightime
N-S
Red 16 sec
Green 40 sec
Amber 04 sec
W-E
Green 12 sec
Amber 04 sec
Red 44 sec

Also-no programmable ICs (except op-amps) can be used.

I do have some ideas (for the digital part mostly - I'll put up a schematic of the circuit as soon as I draw it in Paint!) but the power supply is giving me some problems - I'm not too educated on the current regulation bit. Can anybody gimme some pointers please??

 

[saltydog]

Surely you made a typo with 240V. I'd make a DC power supply from 120V, 60Hz (USA) AC strictly on the basis of safety. Can't you just buy a 5 V DC power supply or do you need to build that too? They're not difficult to build but I'm saying that only on the basis of doing so with 120V NOT 240V Ok?

 

[Shahil]

No typo - specs say 240V 50Hz so that's why I can't buy one!

I'll post a pic of what I've got in mind in a bit (MSPaint again...)

 

[Shahil]

Power Supply circuit (so far)

Here's a diag. of the power supply I got so far. Problem is it's O/P is 12V not 5V (which is a bit of a problem). The diag. is from Protel and it ain't simulating but it ain't simulating! Circuit does work though I'm sure! Also - will the circuit regulate the O/C current to 200mA? Help anyone??