Here it is demonstrated how you can make a continuity tester at home that requires just few components, is reliable, is sensitive, low powered and small. It is powered by 3V battery. You can use the continuity tester to check continuity of signal in electronics circuit. That is it is used whether is conduction on the trace of PCB or on Perf-board.
Testing PCB trace with diy continuity tester
The following picture shows testing PCB traces with the self made continuity tester.
The following picture shows testing trace on Pref-board.
Continuity Tester Circuit Diagram
The following shows diy continuity tester circuit diagram.
Here we have connected a LED and a buzzer at the transistors common collector. The two transistors makes up a sub circuit called darlington pair. A darlington pair has a common collector, the base receives an input message signal, the emitter of the first transistor goes into the base of the transistor. The two tips of a continuity tester is touched on pcb circuit trace(s) and if there is conduction on the tested traces then it completes the conduction path between the pins and the base is turned on. That is the base receives current from the power supply which is 3V and enters into one of the contunity tester pin, goes through the conducting traces and gets into the other tip, into the base. Then voltage drop on the base causes it to turn on the first transistor and then the second transistor(with more current) and into the battery negative terminal. So because the transistors are on, the current flows from supply through the LED and Buzzer into the collector and ends up in the negative terminal of the battery. And due to this process the LED and Buzzer are energized and gets turned on.
Video
Watch the following video demonstration of the diy continuity tester with LED and buzzer alarm works.
This led tester with buzzer works on the same principle as water overflow detector and soil moisture detector.
