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Easy Electronics Projects With Two Semiconductors

Easy electronics projects with two semiconductors can be made using LEDs, transistors and photocells. LEDs are constructed to emit light when powered by a current. Transistors have roles as amplifiers or as electrical switches. Photocells are light detectors usually made from cadmium sulfide.

Use a solderless breadboard for the following projects. Attach the black lead battery holder to one row of the circuit that is ground, and the other red lead to a row that will be the voltage source. Add a 9V battery to the holder after the circuit is built.

LED Series Circuit
- Build a series circuit with two LEDs. Insert a 1k resistor into the breadboard, where both of its leads are in different columns. Add a jumper wire between the resistor's left side and the voltage source. Connect the positive lead of the first LED to the resistor's right side, and place its left end into a different column. Connect the first LED's negative side to the positive lead of the second LED, and insert the negative lead of the second LED into an empty column. Place a jumper wire between the negative lead of the second LED and ground. When the battery is placed inside of the holder, both LEDs will light.
Light Detector
- A light detector can be made with a photocell and an LED. Insert a photocell into a breadboard. Attach one of its leads to the voltage source, and its other lead to one end of a 270-ohm resistor. Attach the other end of the resistor to the positive lead of an LED, and attach the LED's negative lead to ground. Add the battery to the circuit, and shine a flashlight on the photocell. The LED will then light.
Tone Generator
- Create a tone generator with two transistors, a piezo buzzer and a potentiometer. One transistor must be an NPN type, such as a 2N3904, and the other a PNP type, such as a 2N3906. Insert the PNP transistor into the upper section of the breadboard so that it is parallel, with each of its leads in separate columns. Add the NPN to the lower section of the breadboard. Attach the base of the PNP to the collector of the NPN. Connect the PNP's emitter to the voltage source, and connect the NPN's emitter to ground. Add one end of a 0.01uF tantalum capacitor to the NPN's base. Connect the capacitor's other end to the PNP's collector. Insert a 1k resistor parallel into the breadboard, and place a jumper wire between its left end and the voltage source. Connect the left lead of the potentiometer to the resistor's right end. Place the potentiometer's middle lead to the base of NPN transistor, and its right lead to ground. Finally, use a jumper wire and connect the plus side of a buzzer to the PNP's collector lead, and set the minus side of the buzzer to ground. Add the battery to the circuit, and turn the potentiometer's knob to hear the different tones.
Touch Circuit
- Obtain two 2N2222 or two 2N3904 transistors. Insert one transistor into the upper section of the breadboard, and add the other to the lower section. Add a jumper wire between the base lead of the first transistor, and the emitter lead of the second. Attach the emitter lead of the first transistor to ground. Add a 100k resistor so that one end is attached to the base lead of the second transistor, and the other end is inserted into an empty column. Place a jumper wire between the collector lead of the first transistor, and the collector lead of the second transistor. Connect the negative lead of an LED to the collector lead of the first transistor. Attach one end of a 330-ohm resistor to the positive lead of the LED, and the other end of the resistor to the voltage source. Add a battery to the circuit. Place a finger on one end of the first resistor, and another finger on the end of the second resistor, and the LED will light.

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