The ports used in this ultrasonic remote-control transmitter are TTL, requiring a 5 V supply. The transducer is a piezoelectric type, not very common today.
This circuit activates a fan when the temperature exceeds a certain value, sensed by diode Q1. The...
This circuit generates sine low-frequency signals. The frequency depends on the twin-T network....
This circuit has four-time programming keys, according to the table given next to the diagram. The circuit...