Project Hub /Test & Measurement Instrumentation/Multimeters, Voltmeters & Ammeters/Build a Simple Optocoupler Tester Circuit for Fault Detection

Build a Simple Optocoupler Tester Circuit for Fault Detection

Beginner

ANALOG / DISCRETE

< ₹500

3 – 6 Hours

Partial Kit

Build a Simple Optocoupler Tester Circuit for Fault Detection

A compact, battery-powered optocoupler tester built on a dot board that quickly verifies both 4-pin and 6-pin optocoupler functionality using dual LED indicators.

Originally published on CircuitDigest

View original tutorial

Parts You'll Need

This project is sourced from another site, not written by us — this list is our best match of their components against what we stock, not a verified bill of materials. Always check the original blog (linked above) for the actual parts list before buying.

10pcs 5mm RED Diffused Light Emitting Diodes - LEDs Set Rs. 39.00
2-Slot 18650 Holder with Protective Cover and On/Off Switch – Case Rs. 109.00
1200mAh 18650 Li-ion Bat – Reliable 3.7V Power Cell Rs. 129.00
10pcs - 220 ohm 1/4 W Resistor Set Rs. 39.00
400 Points Mini Solderless Prototype PCB Breadboard High Quality Rs. 89.00
MB102 Adjustable Breadboard Power Supply Module (3.3V & 5V) for Arduino & Raspberry Pi Rs. 139.00
Jumper Wire 10 Pin Male To Male 20cm Rs. 45.00
Jumper Wire 10 Pin Male To Female 20cm Rs. 45.00

Selected: Rs. 0.00

This list includes a generic resistor set as a placeholder — it is not matched to the exact value or part number this circuit needs. The correct one is specified on the original source page linked above; check it before buying.

We don't carry yet: Optocoupler (PC817 / 4N35)
Microcontroller IC (DIP) / Chip
Perfboard / Veroboard / Stripboard

Browse all components

How It Works

The simple optocoupler tester circuit is designed to verify the operational health of both 4-pin and 6-pin optoisolators using a compact, analog setup powered by a single 3.7V Li-ion battery. The circuit utilizes an IC base mounted on a dot board to safely hold the device under test. When the push button is depressed, it completes the path to illuminate a red LED which is current-limited by a 470-ohm resistor (R1). This red LED indicator represents the input side of the tester, sending current through the internal transmitting infrared LED of the optocoupler. If the optocoupler's internal phototransistor is functional, it will switch on when exposed to this light. This action allows current to flow from the battery through a second 470-ohm resistor (R2) to light up the green LED indicator, which serves as the output test verification. By observing whether the green LED turns on simultaneously with the red LED when the push button is pressed, a maker can instantly determine if the optocoupler is passing signals correctly or if it has an internal open or short fault.

Why Build This

Quickly test and sort salvaged optocouplers from old electronics boards before using them in new DIY builds.

Troubleshoot benchtop power supplies and isolated circuits by verifying if suspect optoisolators are the source of a fault.

Build a handy, portable piece of test instrumentation for your maker workspace without needing a complex oscilloscope or multi-meter setup.

Real-World Application

Benchtop electronics repair, component salvaging, quality control, and laboratory troubleshooting of optoisolators.

Skills You'll Learn

Component testing and troubleshooting

schematic reading

analog circuit wiring

dot board soldering and assembly

basic power distribution

Safety Precautions

Ensure proper orientation of the battery polarity and correct insertion of the optocoupler into the IC base to avoid short circuits.

Technology Tags

OPTOCOUPLER

PHOTOTRANSISTOR

LED

BATTERY

CIRCUIT TESTING

TROUBLESHOOTING

DOT BOARD

Frequently Asked Questions

Can I test both 4-pin and 6-pin optocouplers with this single circuit?

Yes, by incorporating both a 4-pin and a 6-pin IC base onto your dot board, you can accommodate both standard package types.

Why are 470-ohm resistors used in this circuit?

The 470-ohm resistors (R1 and R2) limit the current flowing through the indicator LEDs and the internal diode of the optocoupler, protecting them from burning out when powered by the 3.7V Li-ion battery.

What does it mean if the red LED turns on but the green LED stays off?

If the red LED lights up upon pressing the button but the green LED does not, it typically indicates a failed or dead optocoupler where the internal phototransistor is no longer switching.

Gallery

This page is part of Kitkraft's Project Hub — a curated collection of electronics & robotics projects gathered from the maker community to help students and hobbyists discover and learn to build. Kitkraft does not claim authorship of the original project, and makes no representation as to the accuracy, completeness or safety of third-party source material. The summary and "How It Works" explanation above are AI-generated, rewritten with reference to the original tutorial — not a reproduction of it. Full credit and a direct link to the original source are provided above. If you're the original creator and have a concern about how your work is represented here, please contact us and we'll address it promptly.

Kitkraft Project Hub — curated from the maker community, credited at the source.

PRJ-01493