Three in One Tester for Audio, Diode, and Circuit

This electronic schematic circuit is a test circuit for audio, diode and circuit. This very handy simple solid state battery operated tester. It works on two 1.2-1.5 AA-batteries.

This three in one tester can be used for :

• audit AF/LF signal
• circuit tester
• diode tester
• 1 KHz tone generator

When you switch S1 OFF the diode/circuit testerschematic can be used.

Source: http://users.belgacom.net/hamradio/homebrew.htm