Elenco Upgrade Kit SC300 to SC750 - Manual (Page 27)

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Project #361
OBJECTIVE: To use a transformer for a louder buzzer.
Turn on the switch (S1). The speaker (SP) generates a buzzer sound.
As in project #353, the relay (S3) is rapidly switched on and off. This
causes an AC voltage on the left side of the transformer (T1). The
voltage is stepped-down and applied to the speaker, generating the
sound.
To make the sound a little louder, replace the 0.1 μ F capacitor (C2) with
a 3-snap wire.
Buzzer, Relay, &
Transformer
Project #362
OBJECTIVE: Make a relay buzzer with speaker.
A speaker (SP) and capacitor (C2) are placed across the coil of the
relay (S3). When the slide switch (S1) is turned on, the relay’s
contacts open and close as in project #353. As the capacitor (C2)
charges and discharges, the speaker generates a buzzing sound.
Buzzer & Relay