Prototype an Electronic Coin-toss Step 3: Connect the Finger-touch Circuit

By Doug Lowe

A good first project for the aspiring electronics hobbyist is an electronic coin toss. It doesn’t literally toss a coin. Instead, one of two lights stays lit when the user removes his finger from two metal contacts, indicating whether the result of the coin toss is heads or tails. Which light stays lit will be essentially random. In this step, you will connect the finger-touch circuit.

The user activates the coin toss by touching the two metal contacts. For the purposes of this prototype, you connect one end of a pair of jumper wires to the circuit and leave the other ends protruding from the end of the breadboard.

Touching the bare ends of these wires with your fingers will simulate touching the metal contacts that you use in the final version of the circuit. The two jumper wires will be inserted into holes in row 9.

  1. Insert resistor R1 from pin 7 of the IC to the +9 V bus.

    Resistor R1 is the 1 kΩ resistor, which should be connected between pin 7 of the IC and the +9 V bus. This resistor has stripes in the following sequence: brown, black, and red. Insert one end of this resistor into hole J15 and the other end into the nearest available hole in the topmost bus strip.

  2. Insert capacitor C1 from pin 2 of the IC to the ground bus.

    Insert one lead of the capacitor (it doesn’t matter which) into hole B15, and then insert the other into the nearest available slot in the bottommost bus strip.

  3. Insert resistor R2 from pin 7 of the IC to one of the metal contacts.

    This resistor is the 10 kΩ. It should be connected between pin 7 of the IC and one of the metal contacts that the user will touch with his finger to activate the coin-toss action. This resistor has the following sequence of color stripes: brown, black, and orange. Insert one end of it into hole H15 and the other end into hole H9.

  4. Connect a jumper wire from pin 2 of the IC to the other metal contact.

    Insert one end of a short jumper wire into hole B15 and the other end into hole B9.

  5. Insert the two jumper wires that simulate the metal contacts.

    Pick out a couple of jumper wires long enough to reach from row 9 and dangle an inch or so over the edge of the breadboard. Insert one end of these wires into holes E9 and F9 and leave the other ends free. Separate the ends of the two jumper wires to make sure they’re not touching; they should be about 1/2″ apart.


These instructions identify specific holes in the terminal strip area of the breadboard using numbers and letters. You might encounter a different numbering system. If so, you can use this template to translate the numbers given in the steps for the breadboard you’re using.