This circuit was found in a Popular Electronics from the 90's. The CMOS integrated circuit used is not very common nowadays. The range depends on the infrared LEDs. R7 can be changed.
This circuit uses a ceramic transducer to emit ultrasound whose frequency depends on C2. The...
We found this Nicad cell charging circuit in an English publication from the 1970s. The circuit can...
This small transistor radio was published in Radio Electronics magazine in November 1957. The...