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.
In fact, we can say that this circuit found in documentation from the 90s, consists of an intercom...
The basic integrated circuits of this 1988 multimeter are no longer very common today, but if...
This circuit is from an old publication of the 70's. It can be implemented with modern transistors like the...