Page 82 - The Basics IA by ETron Circuit Labs

ETron Circuit LabsAdvanced BuildsThese next few pages challenge you to take what you’ve learned and build the labs using only the schematic diagrams.Police SirenTheory:This project uses the 555 Timer IC which works as a VCO (Voltage Controlled Oscillator). When you hold down switch S1, the capacitor C2 is charging, causing the pitch to rise. When you release the push button switch, capacitor C2 slowly discharges and the pitch goes down. You can control how high the pitch goes by holding down the push button switch until the pitch is where you want it to be. You can make a very realistic siren sound with this simple circuit.Procedure:Assemble the circuit and connect a 9-volt battery to the Batter Snap, press switch S1 and you will hear a steadily rising tone in the speaker. When you release the switch, the tone will steadily decrease in frequency. This is the sound of the local police siren.Continuity TesterTheory:This project uses the 555 Timer IC as a source of pulses which are sent to a transistor which drives a speaker. R1, R2, and C1 control the frequency and duty-cycle (duty- cycle is the amount of time the pulse is on compared to the time that the pulse if off) of the pulses coming from Pin 3 of the 555 Timer IC. When you touch the probes to something to check continuity, if there is continuity, the speaker will put out a tone.Procedure:Assemble the circuit and connect a 9-volt battery to the Battery Snap and touch the Probe wires together. You should hear a tone from the speaker. This circuit can be used to check light bulbs, fuses, wires, and resistors for continuity. It is a very common circuit used by electronic technicians.Audio GeneratorTheory:This project uses the 555 Timer IC as a source of variable frequency of pulses which are sent to a transistor, which drives a speaker. R1, R2, R5, and C1 control the frequency and duty-cycle (remember, the duty-cycle is the amount of time the pulse is on compared to the time that the pulse is off) of the pulses coming from Pin 3 of the 555 Timer IC. When you adjust the potentiometer you adjust the frequency of the tone that the speaker will put out. Q1 amplifies the amplitude of the audio signal.Procedure:Assemble the circuit and connect a 9-volt battery to the Battery Snap. You should hear a tone from the speaker. You should be able to adjust the frequency of the tone by adjusting the potentiometer.80