Components and circuits can be tested with this simple circuit. If the resistance between the component or circuit connected between PP1 and PP2 is low, the LED will light up. If it is high or there is no continuity, the LED remains off.
With this we can test components such as capacitors, resistors, diodes, transistors, relays, motors, solenoids and many others. The circuit operates with a 3 V supply and when the probes are separated their consumption is practically nil.
In figure 1 we have the continuity tester diagram and its assembly made in a small terminal bridge. The device can be installed in a small plastic box for ease of use.
The transistor admits equivalent can be used any kind of NPN general use. The probes can also be improvised with large studded nails.
Material list
Q1 - BC548 or equivalent - general purpose NPN transistor
LED - Common red LED
R1 - 10k ohm x 1/8 W- resistor - brown, black, orange
R2 - 470 ohm x 1/8 W - resistor - yellow, violet, brown
B1- 3 V - 2 small batteries
PP1, PP2 - Probes - red and black
Miscellaneous:
Two battery holder, terminal bridge, mounting box, wires, solder, etc.
