This humidity sensor indicates the different levels of conduction of the sensors through an LED bar. The circuit is from Popular Electronics and must be powered by cells or battery.
This 1-transistor reflex receiver was found in a 1963 publication. The coil is for the mid wave...
Found in a European magazine from the 90s, this circuit emits beeps that are several seconds apart to...
This interface or shield circuit for instrumentation was obtained in a publication from the 90's....