Ultrasonic remote control transmitter (CB8397E)

Found in a 90s Popular Electronics, this circuit excites a 40 kHz ultrasonic transducer. The transistor can be a BD135 or other medium power.

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Hand Dryer (CB18786E)
With this circuit it is possible to use a common hair dryer as a hand dryer. The circuit is timed...
8 Channel Encoder with 4017 (CB4530E)
This circuit was obtained from an English magazine from 1979, but can be easily assembled today...
Continuity Tester (CB10617E)
This circuit was obtained in a 1975 magazine, but it can be easily assembled using BC548...