This tester will tell you if a contact or a line is intact by giving out a beeping tone. What is special with this circuit? First, it does not react to low resistance junctions like transistors,
diodes and resistors. Second, it delivers a very low current therefore it cannot possibly damage very sensitive components like CMOS ICs.
Connect a 1 ohm resistor at the probes and adjust P1 until the tester beeps. Then remove the resistor and short the two probes together. In this case, the tester must also beep.
In testing contacts or wires, a resistance of above 1 ohm will prevent the circuit from beeping. The volume of beep is adjustable with P2.
Parts Placement Layout
External Wiring Layout
Electronic Circuits volume 1.0 - Circuit Nr. 74
The complete data of the electronic circuit described above can be found in the following book and is available from Amazon.com.
Click on the image to view the book.