Found in a Popular Electronics from the 90s, this circuit uses common components with several operational options, including the use of an optocoupler that allows its application in a shield.
This amplifier, found in a 1980s documentation, should be powered by a symmetrical source. Modern...
This is a voltmeter with high input resistance. The transistor is germanium. We found it in an...
Up to some minutes intervals can be obtained from this circuit. The circuit can use a lamp (or...