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Metronome – Easy/Moderate

Building the circuit:

To build this circuit you will need: A pack with all these parts is available here

Ω      One 9V battery

Ω      One 9V battery clip

Ω      One 555 timer

Ω      One LM386N Low-Voltage Audio Amplifier

Ω      One diode

Ω      One 27KΩ resistor

Ω      One 1.8KΩ resistor

Ω      One 100KΩ potentiometer

Ω      One 1KΩ potentiometer

Ω      One 10μF capacitor

Ω      One 220μF capacitor

Ω      One 100nF capacitor

Ω      One 8Ω speaker

Ω      One breadboard

Ω      Some hook-up wire

 

The circuit:

Metronome Project Circuit Diagram

In the above circuit you can see the 555 timer in the centre, with the 10μF capacitor and the 100KΩ potentiometer to adjust the tempo of the metronome. The output is then fed through the 1KΩ potentiometer and into the amplifier, which amplifies it and sends it out to a speaker.

 

Once you’ve hooked yours up on the breadboard it should look something like this (but you may have hooked it up differently to ours! part of the fun is working out your own breadboard layout)

Metronome Project Circuit Breadboard assembly

Metronome Project Circuit Breadboard assembly

Once you’ve built it, feel free to mess around with the values of the resistors and capacitors and see how it changes the operation of the circuit!

Overview/How it works:

This circuit uses a 555 timer, along with a capacitor which charges through D1 and R2 and provides the interval for the pulse, changing the 100K potentiometer changes this interval and so means you can change the speed of the pulses. Because the beat is always steady it can be used as a metronome to provide a tempo.

On its own this circuit does not produce enough sound to be helpful because you can barely here it. We put the output of this circuit through an LM386n low voltage audio amplifier and a potentiometer so we can adjust the volume. The amplifier is configured to a gain of x20 which is the standard gain of the chip, adding different value RC circuits (Resistor Capacitor circuits, which are simply just a resistor and a capacitor in series) across pins 1 and 8 will change the value of the gain. E.g. a 10μF capacitor with no resistor across these boosts it to a gain of x200, or a 10μF capacitor with a 1.2KΩ resistor gives it a gain of x50.

The output from this chip is then sent through a 200μF capacitor, which is used to smooth out any ripples in the voltage and improve sound quality and finally out to an 8Ω speaker.

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