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Simple Mini Alarm Circuit

2015-01-12 09:34  
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Here is very simple alarm circuit. This novel buzzer circuit uses a relay in series with a small audio transformer and speaker. When the switch is pressed, the relay will operate via the transformer primary and closed relay contact. As soon as the relay operates the normally closed contact will open, removing power from the relay, the contacts close and the sequence repeats. The speakers tone is thus proportional to relay operating frequency. The capacitor C can be used to “tune” the note. The nominal value is 0.001uF, increasing capacitance lowers the buzzers tone. Here is a schematic drawing:

Simple Mini Alarm Circuit 400x295 Simple Mini Alarm Circuit








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