Flashing Traffic Lights

This Instructable will show you how to make simple flashing traffic lights with just four components (Flashing LED, two bright LEDs and 9 V battery). Flashing LEDs might cost more than bright LEDs. You only need one flashing LED. The rest of LEDs can be bright LEDs or even normal LEDs. I used 10 mm (1 cm) thickness LEDs.

The first video shows the flashing traffic lights for 11 seconds. The second video shows photos of all the step in making the flashing traffic lights for about 50 seconds.

Components: 10 mm Flashing LED - 2 (you might need spare), 10 mm yellow bright LED - 2 (you might need spare), 10 mm green bright LED - 2 (you might need spare), 9 V battery harness, 9 V battery, cardboard, transparent sticky tape, electrical tape, lead free solder, bottle/jar lids (for drawing on cardboard).

Tools: 60 W soldering iron, soldering iron holder, wire stripper, pliers, scissors, pen/pencil, ruler, pin (for making holes).

Optional tools: circuit holder, drawing compass.

The sum of the voltage across the three LEDs is equal to the voltage across the battery.

Vs = Vled1 + Vled2 + Vled3

Vs = 5 V + 2 V + 2 V

= 9 V

The 9 V is the voltage across the 9 V battery.

The flashing LED that I used has a forward voltage of 5 V according to the electronics store specifications listen on their website. Some flashing LEDs have forward voltages of only 3 V. Then you would need a 7 V power supply. Not 9 V power supply. You can use 7.5 V five AA/AAA switched battery holder.

This circuit would work with 6 V power supply (four AA/AAA batteries) but each of the four AA/AAA batteries needs to be fully charged to 1.5 V. The circuit would not work with four 1.2 V rechargeable batteries because the total voltage would be only 4.8 V not 6 V. You can watch the video of the circuit connected to 6 V power supply here: https://www.youtube.com/shorts/OFAUB28dW9Q

Use pen/pencil, ruler and scissors to draw and cut out 15 cm by 3 cm rectangle.

Use the lead free solder spool or bottle/jar lid to draw three circles and cut them out with scissors.

Use scissors and transparent tape to make cones from the three circles and put them next to each other in a row as shown in the first photo. You can use those cones as reference to draw the dots with a pen. Then make holes with a pin.

Insert the LEDs and connect them as shown in the circuit diagram. Not that the longer LED pin (the anode) should be placed on top as shown in the diagram because the longer LED pin is the positive pin, the shorter pin is the negative pin.

Use wire stripper to strip the 9 V battery harness wires.

Connect 9 V battery harness to the circuit and the 9 V battery to the battery harness. Test the circuit.

Attach the circuit to circuit solder and use the 60 W soldering iron to solder the connections. This step is necessary to prevent poor contacts due to rust.

Seal the contacts with electrical tape to avoid short circuits.

Roll the 15 cm by 3 cm rectangle into a tube and seal with transparent tape.

Widen the cone holes with scissors by rotating the scissors in clockwise and anticlockwise direction.

Insert the cones into LEDs. The final step is making a larger cone from a large jar lid to make a bigger cone (draw a circuit and cut out with scissors) for the traffic light stand as shown in the second photo.