This circuit was found in an article in Electronics Now magazine from March 1997. The transistors are general purpose, and the indicator is a 1 mA full scale analog type.
This circuit uses two sensors that are placed at the intersection of a miniature railroad, causing the LED...
Many oscilloscopes have high impedance inputs that make it difficult to observe high frequency signals...
This wired intercom circuit was found in a March 1965 Radio Electronics. The circuit uses two...