This circuit was found in an American 1980s documentation. It analyzes the exhaust gas of a vehicle using a special sensor. The indicator is a milliamperimeter.
Found on Popular Electronics this circuit has variations found throughout this site and section....
This effect for guitar was found in an English magazine from 1978. The transistors can be the most...
This circuit was found in a 90s Popular Electronics. It is possible to analyze the voltages of an...