Battery-operated alarm clock - has electronic buzzer using transistor oscillator connected to drive coil for vibrating membrane

摘要

The membrane is vibrated at an audio frequency by an electromagnet having a drive winding and a control winding, the drive winding connected in the collector circuit of the oscillator transistor and the control winding connected in the base circuit of the transistor. A capacitor and a resistor are connected in series with the control winding, which is shunted by a further resistor. - A third resistor is connected in parallel with a series circuit comprising the latter capacitor, an alarm switch and the battery, with the collector capacitor, an alarm switch and the battery, with the collector-base path of a second transistor of opposite type, connected in series with a diode across this resistor.