Page 86 - The Basics IA by ETron Circuit Labs

ETron Circuit LabsAdvanced Builds 3Variable Speed LightsTheory:This project uses the 555 Timer IC as a variable speed “clock.” As you adjust the amount of resistance between Pins 6 and 7, you adjust the speed of the pulses exiting Pin 3.When Pin 3 is HI, LED 2 lights up, and when Pin 3 is LO, LED 1 lights up. The 220 Ohm resistors keep the current from being too high and burning out the LEDs.Procedure:Assemble the circuit and connect a 9-volt battery to the Battery Snap and you will see the LEDs blink back and forth. The speed of the blinking can be adjusted by rotating the shaft of the potentiometer.Nose BeeperTheory:This project uses the 555 Timer IC working as a clock, putting out pulses from Pin 3. Transistor Q1 amplifies these pulses and sends them to the speaker. The loudness of the speaker can be increased by mounting the speaker in an enclosure or adding more stages of amplification.Procedure:This experiment uses human bodies like wires. Assemble the circuit and connect a 9-volt battery to the Battery Snap and hold one of the probe wires between your fingers while a friend holds the other. You can make a chain of people as long as you want, extending from each wire, and the circuit will work the same. When you reach across and touch the nose of your friend, the circuit will beep. That is because by touching your friend you complete the circuit and make the speaker sound.Insanity AlarmTheory:This circuit is a two transistor oscillator with a speaker. When the resistance of the photocell is sufficient for the oscillator to being working, you will hear a sound from the speaker. As soon as light hits the photocell, the resistance reduces and the oscillator turns off. The 10 Ohm resistor prevents too much current from flowing in the speaker.Procedure:Assemble the circuit and connect a 9-volt battery to the Battery Snap and there should be no sound emitting from the speaker. Now, find a dark location and put this circuit in it. The speaker should put out a high-pitched sound. As soon as you turn on the lights, the sound will stop. This is fun as a game. Hide the insanity alarm in a room and turn out the lights and see who can find it.84