Simple LED Tester Circuit

This circuit is like a tiny doctor for your LEDs.

It helps you check if your fancy light emitting diodes are working properly.

Imagine a little setup with a battery, some special resistors like tiny traffic lights for electricity, and clips for the LED.

You connect the LED and the circuit checks if it lights up.

If it does, your LED gets a clean bill of health.

Circuit Working:

Parts List:

In this article while multimeters have a Vf function barely lights up green, blue or white LEDs.

This is particularly handy for checking SMD LEDs which are otherwise easy to install incorrectly.

It can also be used to check a string of LEDs one at a time to ensure they are all installed correctly.

3V is enough to turn on any LED but is within its reverse breakdown voltage rating.

The short circuit current is approximately 30mA.

For the LED tester construction, its soldered two 47Ω, ¼W resistors to the two battery terminals and insulated the leads with teflon tubing.

Stripping off PVC insulation from wires will also work fine.

Put a kink toward the end of the lead to keep the tubing in place.

No problems with the leads breaking, they will eventually fatigue and break, but it is a very simple repair just avoid bending them sharply.

For the battery, 3V lithium battery salvaged from a circuit board.

Good ones have a voltage that exceeds about 3V.

Alternatives are the CR123 or DL123 photoflash battery or you can simply tape two 1.5V AA or AAA batteries together and connect them in series.

Formulas and Calculations:

It is only a circuit for determining a CR123A batterys voltage.

The voltage from the battery is lowered to a level that is safe for the multimeter probes using the two 47 ohm resistors.

The voltage drop between each resistor may be determined using the following formula:

V = I * R

where,

• In volts V is the voltage drop across the resistor.
• I is the amperes A of current flowing through the resistor.
• R is the resistors resistance expressed in ohms Ω.

The voltage drop across each resistor in this instance is:

V = 0.025A * 47Ω = 1.175V

Consequently, there is a 2.35V total voltage loss across both resistors.

This indicates that when the probes are attached to the circuit, the multimeter will detect a voltage of 3V – 2.35 V = 0.65 V.

The current limiting resistors value may be found using the following formula:

R = (V_cc – V_f) / I

where:

• R is the current limiting resistors resistance measured in ohms Ω.
• The batteries voltage, expressed in volts V is Vcc.
• The LEDs forward voltage, expressed in volts V is Vf.
• I is the intended current in amperes A flowing through the LED.

For example, if you wish to run a current of 20 mA through a red LED that has a forward voltage of 2V, the current limiting resistors value would be:

R = (3V – 2V) / 0.02A = 50Ω

For this, a 47ohm or 51ohm resistor will work.

How to Build:

To build a Simple LED Tester Circuit you need to follow the main assembling steps:

Prepare the resistors:

• Solder one end of each resistor to one of the battery terminals.
• These resistors will limit the current flowing through the LED.

Insulate the leads:

• Slide a piece of teflon tubing or use stripped PVC insulation over each lead of the resistors to prevent short circuits.

Secure the insulation:

• Put a kink in the tubing or insulation near the end of the leads to keep them in place.

Connect the battery:

• Connect the other ends of the resistors to the positive and negative terminals of the 3V battery or the combined AA or AAA batteries.

Test the LED:

• To test an LED, touch its positive lead anode to the positive terminal of the LED tester and its negative lead cathode to the negative terminal.
• If the LED lights up it is working correctly.

Repairing broken leads:

• If the leads break, they can be repaired by re soldering or replacing the resistors and re insulating the leads.

Note:

• Remember to exercise caution when working with batteries and soldering irons to avoid injury or damage to the components.

Conclusion:

A LED tester circuit is a simple yet effective tool for testing the functionality of light emitting diodes.

By providing a safe and controlled environment for the LED, it helps ensure proper operation and prevents damage.

This makes it a valuable tool for electronics enthusiasts and professionals alike.

References:

LED Tester