Bird Feeder Monitor Circuit

The first amplifier circuit is a bird phone. In this circuit, the electret mike (MIC1) is mounted in the neck of a large plastic funnel. The amplifier, built around an MC34119 (which is available from D.C. Electronics, P.O. Box 3203, Scottsdale, AZ 85271-3203; Tel. 800-467-7736, and elsewhere), is then placed outside of the funnel with the pickup facing a nearby bird feeder. The output of the amplifier is then connected to a 16- speaker. The amplifier`s voltage gain is determined by the values of the input resistor (Rl) and the feed-back resistor (R3 and R4, respectively).

The differential gain of the amplifier is given by: R2 + RJR} x 2. With the component values shown, the maximum voltage gain is about 270. This permits listening to the activity at the bird feeder.

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