This circuit is from a 1991 publication. The integrated circuit used is an integrated radio from that era.
This low-frequency circuit for alternating signals is from an early American 1980s documentation. The...
This circuit uses a voltage comparator and can produce signals up to 20 MHz. The resistors R are...
This 3-step level indicator uses only passive components. LEDs are common and trimpots can be 4k7...