Found in a 1980s German publication, this circuit tests batteries by type. The circuit is based on a range of LEDs of different colors and is given a table with indications for various voltage ranges.
This circuit operates with an AM radio tuned to or near 900 kHz if there is a station at this...
This circuit was found in a 1965 General Electric documentation. SCRs and unijunction may be...
Found in a 90s Popular Electronics, this circuit uses a simple 9 V source. The power can be used...