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build this simple bat detector so that you will be prepared to go on safari for bat sounds in the spring.

The detector makes sounds at frequencies of 10-300 kHz audible to human beings. The conversion is ca ried out either by a superheterodyne circuit or a frequency divider. Although it enables listening to bats, and a number of other mammals, as well as insects, the detector isparticularly useful

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The main features and specifications are: hybrid analogue and digital circuitry, low current consumption - less than 5 mA in standby, selectable division ratio, etc.

rectifier circuit is at reference voltage and it moves towards the positive supply rail when a signal is input. The latter digital stages of the bat detector need the amplitude to be referenced to the negative battery voltage. In order to achieve this, a variable bias voltage is added to the positive input

that purpose. It is based on a special integrated circuit which contains an IR irradiance to frequency converter. In other words, the converter's output frequency provides an indication of the measured light intensity. A very handy and simple circuit!

The function of this circuit is to sound a buzzer, or, optionally, actuate a relay, when a certain moisture level is detected between a pair of probes.

Having an apartment in Cyprus, each evening I can see bats fly past my balcony on the way to their feeding grounds. I decided that it would be a good idea to ‘tune in’ to the bats as they flew past. The idea culminated in a bat detector that’s possibly the most refined of its kind published in

Here’s a novel way of listening to bats over the Summer. Put the receiver — powered by four AA (R6) cells — on a window-ledge, for example, preferably aiming the ultrasonic detector towards an outdoor light or some trees. Run out a few metres of cable so as to install the small loudspeaker

This audio peak detector allows a pair of stereo channels to be monitored on a single LED.Identical circuitry is used in the left and right channels. Use is made of the switching levels of Schmitt trigger NAND gates inside the familiar 4093 IC. The threshold level for gate IC1.A (IC1.B) is set with