Found in a 90s R-E Experimenter Handbook, this circuit has a greater gain than the previous one for presenting two stages. The integrated circuit used is uncommon today.
January 2017 - Omron G7L-x relays for PCB mounting can now be purchased from Mouser Electronics. These...
The circuit below is from National Semiconductor's Linear Applications Handbook. Integrated...
This circuit appears elsewhere on this site. This is from an American 80's circuit manual....