Ultrasonic Transducer
Calectro J4-815 

1970s Vintage ~ New Old Stock
(Originally sold by You-Do-It Electronics, Needham, MA)

The Calectro J4-815 is a classic, inexpensive 40 kHz 0.1Watt ultrasonic crystal transducer.
Operating as both a transmitter and receiver, it has historically been used in hobbyist electronics projects (like intrusion alarms and blind-spot detectors) and early research prototypes.

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