Hi, am kind of new to this forum, pleas take it easy on me and help me out. I am required to build a traffic light using LEDs as my school project. the timing sequence required is 6o seconds for Red, 55 sec into the time Yellow come up and glow along side with the RED for about 5 seconds, then goes of for the Green to come up for like 60 seconds and 55 seconds into the time the Yellow comes up again and glow along side with the Green then give way for the Red to come up just like the normal traffic light.

I've tried building two different circuit configuration using 555 timer and a decade counter but could not achieve the rquired result.

I've also tried using series of capacitors and variable resistors in adjusting the timing frequencies still could not give me the exact result.

The power supply unit I've built, produces 12V regulated DC, Using 220V to 12V transformer.

I'll appreciate every effort towards helping me get the required result.
Please, also provide circuit diagram to help understand the connections.

Thanx,

Hudson

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...Always looking out for the best!

 

Hi:

Here is something you can try. Build a 5sec period clock (use a 555 at 12V), and feed it into three cascaded decade counter/decoder(4017 at 12 V). First 12 OP's of the counter chain feed a resistor each into an NPN with red LED (and resistor) in the collector). Next 12 OP's feed a second similar arrangement for the Green LED. The Yellow LED is fed from the 11th, and 23rd OP's. If you wish the Green to be off during the yellow period, it is fairly easy to figure it out too. The main advantage of this approach is you have one clock source. Another alternative is to do it with delays (monotables), but then you will have to adjust each delay separately.

Jem

 

i don't know if your project requires you to build this device using integrated circuits or not, but if not, you could us contactor relays and timers configured to drive the lights. it would be easy enough to design and build. message back if you want further explanation or schematics

adam

 

If they will let you use a microcontroller, you can do this with 1 chip and your leds. It is also quite a bit more flexibly than discrete 74XX based designs. A traffic light is best modeled as a finite state machine. In this case, the timing situation (and particularly how to generate it) complicates the state machine. You could easily do this state machine in a micro however.

 

I agree! (Provided you are allowed to use a uC). My personal favorite is the AVR series. With careful management, you can get everything done for under $50.

Good Luck,

Jem

 

My personal favorite is also the AVR -- with just a few parts, I built my own programmer (with better line drivers) in an hour or so that fits entirely inside a d-sub and provides the ISP header.

 

I use a Pony Prog for projects requiring ATMega8, and a simple parallel programmer for the 2313, 8515 type devices. Mostly I program in assembly (the Atmel assembler has its quirks, but I am used to it).

Jem