This 1968 Mullard circuit detects fire by smoke using LDR-type sensors. The circuit makes use of transistors of the time that admit equivalents.
This bargraph or moving bar with LEDs is from a Radio Electronics magazine from June 1978. The...
In the figure below we have two triggers made with the LM3900 transconductance operational...
This circuit for musical instruments was found in a 90’s Elektor. The circuit still applies, as the...