How to make a handy Pocket continuity Tester

A handy Pocket continuity Tester

Introduction

You might have encountered difficulties in testing vital yet simple components on the service bench, such as Wires, Fuses, Switches, Transformer windings, coils, connections, or PCB tracks for continuity.  Here’s a handy continuity tester that fits perfectly in your pocket, runs on a single button cell, is extremely energy-efficient, and alerts you with an audio tone whenever continuity is detected. It is compact, reliable, cost-effective, and built around the CMOS IC 3909. It is simple to assemble and use. You can carry it in your pocket when you are out. Let us continue with how to assemble this simple gadget here. 

Know your circuit

The circuit is very straightforward and uses a minimum of components. The simplicity is that it works on just a button cell. 

  

Know your design

This continuity tester is configured around IC 3909, which works on just a single button cell. This handy little tester is designed to check continuity in wires, circuits, and components while giving an audio beep through a small speaker whenever continuity is detected. No need for bulky multimeters — this lightweight, portable solution is all you need in your pocket!

The circuit is powered by a coin-sized button cell, making it extremely efficient and easy to carry around. Using the IC 3909, the design becomes reliable and effective while keeping the component count minimal. Whether you’re a beginner in electronics or a DIY enthusiast, this project will give you hands-on experience in circuit building.

This project is perfect for students, hobbyists, repair technicians, and DIY lovers who need a quick, portable solution for continuity testing.

Speciality of the design

What types of components can this tester test and show results for?

As we handle day-to-day components in our service centres and homes, such as open fuse, open switch, open or short diodes, LEDs, Speaker voice coils, transformer windings, relay coils, ordinary coils like radio coils, etc. This tester can test for the continuity of components up its 100 ohms of resistance. 

This tester is very useful when you struggle with PCBs. It can test the continuity as well as shorts in PCB copper tracks. The service technicians' handy tool is a welcome project my many electronics enthusiasts. 

Working of the circuit

The circuit is energised with a single 1.5V button cell. However, one can use a Pen torch cell type AAA.  Connect the test probes to the points A and B as shown in the picture.

                    

An audio sound is produced in the speaker when probes are shorted. This means that the circuit is working as shown by the continuity. Components under test are to be connected between Probes A and B.

As an illustration, let us take a 5Amp. glass fuse Connect both test probes A and B to both sides of the fuse  If you hear an audio sound, the fuse is in good condition. That means the fuse continuity is there. No sound from the speaker indicates that the fuse is open. In such a way, the components under test should be connected and tested.    

Know your assembling

For your convenience in hooking up the circuit, the IC 3909 pin details are shown here.  

Test probes colour code and connecting terminals are shown in this picture. 

Spare parts list

IC -----------------------   LM 3909.......................1 no.

C1 Capacitor--------------10 MFD 12V...................1 no.

C2 Capacitor--------------100n............................1 no.

R1 Resistor----------------1K ohms.......................1 no.

Ls Loud speaker-----------16 ohms 1 1/2 inch .......1 no. 

B   Battery-----------------1.5V button cell ............1 no.  

For assembling the circuit Solderless Breadboard or general purpose PCB can be used. Use 8 pin DIL IC socket to insert CMOS IC LM 3909. A tiny loudspeaker of 1.5 inch with 16 ohms impedance can be used. No on/off switch is required since the current consumption of the circuit is very minimum and the circuit gets power supply only through the connection of A and B probes that too when a component is connected. All the spare parts are easily procurable in the local market from electronics stores. Surprisingly the gadget can be housed ina small soap box. As such it can easily slip into one's shirt pocket. Hence it is avery handy pocket continuity tester always ready when you are out of the home for outdoor service purpose. 

A simple continuity tester circuit is available here.

Conclusion

A simple DIY project for novices, hobbyists and electronics enthusiasts. A special handy tool for the service personal avoiding the bulky multimeter when you are engaged in outdoor service. Please give your comments and suggestions on this post. Thanks for happy reading and doing.