Micro siren (CB21234E)

This circuit with the LM3909 can be powered with voltages from 3 to 5 V. We found it in a Popular Electronics from the 90s.

2 LED flasher 2 (CB20422E)
This version is a variation of the previous circuit, inverting the position of the transistors to have the...
Band Pass Filter 741 (CB15619E)
A frequency range determined by the network of resistors and capacitors with negative feedback and input...
Car Battery Monitor (CB4374E)
This circuit was found in an English magazine Radio & Electronics Constructor of February 1977....