How to Make a Traffic Signal Circuit Design

Creating the Circuit Design

• 1

  Determine the timing sequence. Traffic circuits switch between three different-colored lights: red, yellow and green. Generally, the circuit illuminates the yellow light for a shorter amount of time than the other two lights. Determine precisely how long you want each light to stay on.

• 2

  Draw a circuit diagram for the traffic timing circuit on a piece of paper. There are many different ways to design this kind of circuit, but in any configuration, you will need a 555 timer circuit, a 4017 decade counter, resistors, capacitors and LED lights. There are many traffic light circuit diagrams available on the Internet. One such free circuit is published by The Electronics Club.

• 3

  Draw the circuit board layout in a computer-aided design program.

Creating the Circuit Board

• 4

  Print the circuit drawing. Once you have created your CAD file, use a laser printer to copy it to glossy magazine paper.

• 5

  Transfer the circuit diagram to a blank printed circuit board. Place the printout of the diagram face down on the blank PCB. Then press a hot iron to the paper and the board for one minute. Soak the board in water for one minute and peel the paper from the surface. You should see that the toner has transferred to the board.

• 6

  Etch the circuit onto the PCB. Submerge the PCB in an etching solution such as ferric chloride for 15 minutes. When you remove the PCB, all the copper should have dissolved away except for the copper under the toner. Rinse the board thoroughly and remove the toner with cotton wool and nail polish remover.

• 7

  Drill holes into into the PCB according to the schematic. These hole are where the wire leads for each electronic component will be soldered to the board.

Assembling the Traffic Signal Circuit

• 8

  Connect the passive components including the resistors, capacitors and potentiometer. Fit the leads of each component into their appropriate holes and use the soldering iron and solder to join the component lead to the PCB.

• 9

  Connect the semiconductor components. Both the diodes and the LEDs used in this circuit are semiconductors. Solder them to the PCB in the same manner as the passive components.

• 10

  Connect the integrated circuits. Due to their sensitivity, do not solder the integrated circuits directly to the PCB. The heat from the soldering iron will cause the chip to malfunction. Instead, solder the IC socket to the board and insert the chip into the socket.

• 11

  Solder the 9-volt battery clip and the on/off switch to the PCB. Double-check the polarity of the battery clip. The black wire is negative and the red wire is positive.

• 12

  Test the circuit. Plug a 9-volt battery to the clip and flip the switch to the on position. The lights should cycle through red, green and yellow; with yellow being the shortest interval.