This circuit uses an LDR as a sensor to trigger an LED indicator at a preset lighting level. The power supply does not have to be symmetrical.
This traditional two-tone alarm configuration with the 4011 integrated circuit was found in a 1998...
This extremely slow circuit produces one pulse per month and can be used in a timer. We found it...
This circuit is from an 80's documentation, making use of PUTs that are not currently common...