Traffic Light Using 74LS93 and GAL


January-May, 2013

General Description:

This is my project for Digital System Theory class last semester. I had to made something by using IC counter and IC General Arithmatic Logic(GAL). I made this in a group with my friends.


-Soldering iron
-Solder wire
-Altium Designer

Materials and Components:

-Breadboard/simulation board
-Red 7 segment common cathode
-Green 7 segment common anode
-LED(s): Red, Yellow, Green
-IC counter 74LS93 and 74190
-IC BCD to 7 segment 74LS47(for 7 seg common anode) and 74LS48(for 7 seg common cathode)
-IC JK-FF 74LS76
-IC GAL 16V8
-IC timer 555
-IC 4071(OR gate)
-IC 7401(NAND gate)
-Resistor 10K ohm
-Capacitor 10 uF and 47 uF
-9V Battery

We did not make this traffic light by using the microcontroller, as you can see in this article's title, we made this traffic light just using mod 16 counter 74LS93, so this traffic light miniature had limitation in its counter. We had to divide the counting time into 3 part, and set the frequency of output clock from IC 555 to produced 1 Hz signal, it means one pulse at a time, you can use the calculator for IC 555 in here. So, we could set 12 seconds for Part 1(Red Countdown), 1 second for part 2 (Yellow Countdown) and 3 seconds for part 3 (Green Countdown). I used IC GAL just to separated the output from 74LS93 for 1st and 2nd way and 3rd and 4th way.

Traffic Light Concept

Final concept for the traffic light

Traffic Light behavior produced by 74LS93

The Schematic

Green Light Countdown

To make the countdown for green light, I assembled the JK-FF as you can see above

Traffic light red countdown

Traffic light 1st and 2nd way

How it works:

The timer 555 produced the 1 Hz signal to make every IC(integrated circuit) works. The IC counter 74LS93 would start counting from 0 to 15. The output from 74LS93 would be divided into 4 traffic light in cross roads, how was it divided? Look at the picture of Traffic light behavior. By understanding its behavior, I can make the countdown for the traffic light. As you can see, the red light will be on for 12 seconds, so I set both 74190 to display number 12(by cascading them), 74190a will start the countdown from 1 to 0 and 74190b will start the countdown from 2 to 0. Everytime the 74190b finish counting, it'll send a signal to make the 74190a counting.

74190a 74190b
1 2
1 1
1 0
0 9
0 8
0 7
0 6
0 5
0 4
0 3
0 2
0 1

I did almost the same thing for green light countdown, but because I used the different IC so I couldn't do exactly the same. I used the JK-FF(s) for green light countdown with mod 3 up counter schematic, but I reverse its logic so it became a down counter.

What did we do with the GAL?
Look at the schematic of traffic light without countdown. We programmed the GAL as that circuit.
By doing so, we made the traffic light circuit more simple.

Originally published in my previous blog on 13/05/13

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