lectronic Construction

Tone generator project

In order to record the information about an electronic circuit, you need several different things:

• Schematic diagram (a diagrammatic representation of the circuit)
• PCB layout (A diagram showing where the warts should be placed)
• Parts list (A list of all the parts that go into the circuit)

Schematic diagram

How it works
At the centre of the circuit is an IC or Integrated Circuit (labelled IC1), this part is a 555 timer. The timer IC outputs pulses, the duration of these pulses is determined by the voltage on the input threshold pin. When this pin reaches a certain voltage the output changes. The voltage on the threshold pin is gradually changing as capacitor (C1) stores charge. The speed at which the capacitor stores this charge is set my the resistor (R2) and the faster this is charged the quicker the output changes and the frequency that drives speaker is quicker. The faster this frequency the higher the pitch of the tone that is produced.

PCB layout

Parts list

PCB Ref(s)	Description	Quantity
R1, R2	10K resistor pre-set	2
R3	2K2 resistor	1
R4	220 resistor	1
C1	0.1 uF cap	1
C2	100 uF cap	1
Q1	BC337 - NPN transistor	1
IC1	NE555N	1
PL2	38 mm speaker (8R)	1
PL1	PP3 battery clip	1

Operating instructions

• A tone will be produced when the switch (PL1) is closed
• The frequency of this tone is determined by R2 and can be from 0Hz to 8Hz
• The volume is set by R1

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