Ultrasonic Proximity Sensor (CB21312E)

This circuit was found in a Popular Electronics from the 90s. The circuit uses a ceramic capsule as an emitter and detector.

High Impedance Microphone Preamplifier (CB18257E)
This high-gain circuit uses junction FETs (JFETs) and must be powered by somewhat high voltages. The...
Binary Display 7400 (CB22436E)
This circuit counts 1 per second, displaying the value in binary. The circuit is TTL and must be...
Sensitive Geiger Detector (CB5925E)
Critical components of this project are the Geiger tube and the 300V battery. The battery can be...