This circuit was found in a Dutch documentation from 1970. The circuit makes use of semiconductors that have current equivalents and is indicated by a 0-5 mA milliammeter.
This circuit is given in two versions, having been found in a publication from the 90s. The second...
This circuit was found in an ancient American documentation. Used integrated circuits are uncommon...
This Texas Instruments circuit uses a phototransistor to fire a TTL trigger port. Other...