Prototype an Electronic Coin-toss Step 4: Complete the Circuit
In order to complete the electronic coin toss prototype, you will complete the circuit by connecting the power supply. Your prototype won’t literally toss a coin. Instead, one of two lights will stay lit, indicating whether the result of the coin toss is heads or tails. Which light stays lit will be essentially random.
Here’s how to connect the power and complete the circuit:
Connect the battery snap connector.
The leads on the battery snap connector use stranded rather than solid wire, so you'll need to prepare them a bit before you insert them into the breadboard.
Use your wire strippers to strip off about 1/2″ of insulation from the end of both leads.
Use your fingers to twist the leads as tightly as you can, so that no individual strands are protruding from the very tip of the wire.
Insert the red lead into the last hole of the topmost row and insert the black lead into the last hole of the bottommost row.
Connect the 9 V battery to the snap connector.
The red LED should immediately light up.
You can now test the circuit by touching both of the two free jumper wires. Pinch them both between your thumb and index finger, but don't let the wires actually touch each other.
The resistance in your skin will conduct enough current to complete the circuit, and the LEDs will start alternately flashing, red, green, red, green, and so on. They will continue to flash until you let go of the jumper wires. Then, one or the other will stay lit. When you touch the wires again, the flashing will resume.
Notice that if you squeeze the wires tightly, the rate at which the LEDs flash increases. If you squeeze tight enough, the LEDs will flash so fast that both will appear to be solid on. The LEDs are still flashing alternately, but they're flashing faster than your eye's ability to discern the difference, so they appear to be on constantly.