# The 555 Timer IC

The 555 timer is an Integrated Circit that is most commonly found as a DIP (Dual in Line Package) with 8 legs. It has many different different applications but it is primary use is often in trimming or oscillating circuits. In this example we are going to make a circuit that turns an output pin on and off rapidly so that a device such as a speaker can make sound by moving back and forward to create sound waves that we can hear.

Video:

Instructions:

1. Identify all of the parts required for all three circuits bellow in the parts list:
2. Before starting ensure power supply is not connected
3. Use the Fritzing Breadboard Layout and Schematic Diagram images to connect the components with prototyping wires to complete
4. Record findings in learning journal.

Diagnosing problems:

• If any component is getting hot disconnect the battery.
• Ensure a resistor is used in the circuit or LED will be burned out and damaged
• Ensure LED positive leg (longest) is connected to positive side of circuit
• Check battery voltage with multimeter in Volts DC mode
• Try a different LED in case it has been burned out (ensure you are using a resistor!)
• Look at breadboard picture bellow and ensure all connection are correct.

Parts List:

Part Qty Name
VCC1 1 4.5V – 6V Battery Supply
R1 1 1k Ohm Resistor
R2 1 10k Ohm Resistor
R3-5 3 1K Ohm Resistor
C1-2 2 10nF Cap
C3 1 10uF Electrolytic Cap
J1 1 Piezo Speaker

Fritzing Breadboard Layouts and Schematic Diagrams:

Frequency Calculation:

f = frequency in hertz (Hz), R1 & R2 = resistance in ohms (Ω), C1 = capacitance in farads (F).

To calculate the stylus touching position A:
R1 = 1kΩ = 1000 Ω
R2 = 10kΩ + 1kΩ = 11,000Ω
C1 = 10nF = 0.01uF = 0.0000001 F

f = 1.4 / ((R1 + 2 x R2) × C1)
f = 1.4 / (1000 + 2 x (11,000)) x 0.0000001
f = 1.4 / (23,000) x 0.0000001
f = 1.4 / 0.0023
f = 608.7 Hz

Try calculations for Position B and C.

Extra Teaching Material:

• What happens when you add a second capacitor of the same value in parallel to C1.
• What happens as you add more resistance to R2 in series? Why?
• Use an instrument tuner (or mobile app) to listen to the sound that is being generated and determine the frequency. Some multimeters can also measure frequency
• Consider why the results of the formula does not have exactly the same frequency results as the measured frequency?

Quiz:

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Finished? Lets have a go at the Solder the Stylophone Project

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