Sound triggered flash (CB8703E)

Found in 90s Popular Electronics, this circuit fires an old camera flash of the type with a xenon lamp from the sound captured by a microphone.

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Thermal monitor (CB9307E)
This circuit was found in an Elektor from the 90s. The integrated circuit is uncommon today. This...
1 kHz Bandpass Filter (CB24388E)
Found in July 1975, Radio Electronics magazine this circuit can use any operating circuit,...
Touch on off switch (CB9519E)
Found in a Hands-On Electornics, this touch biestable can control loads that depend on the SCR....