Low power NBFM transmitter

The transmitter is a crystal-con-12 trolled, battery-powered, one-chip narrowband frequency modulation v(NBFM) model for operation in the 27- m band, primarily as a wireless microphone*. The circuit is an application of Motorola’s MC2833 single-chip VHF narrowband FM transmitter IC, designed to work in the 27-MHz band. The transmitter output power is about 10 mW (+10[…]

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State of battery indicator

Many battery-operated appliances have an LED indicator that shows the state of the battery. If the battery is almost flat, the LED flickers. The circuit described enables this facility to be built into apparatus that has no indicator. The drop across D1 (LED) depends on the type of LED and is normally around 2 V.[…]

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