LED tester with adjustable current

This is an easy to build LED tester with several useful features.

- Adjustable current of 1 mA to 20 mA - Evaluate brightness and efficiency

- Vf (forward voltage drop) measurement - Needed to calculate resistor value

- LED will not be damaged if connected backwards - Voltage is limited to 5 volts

- Power on / open circuit / reverse polarity indicator - Indicates bad or improper connection

Step 1 Parts and Schematic

Parts required:

47 ohm resistor
100 ohm resistor
1 K ohm resistor
1.5 K ohm resistor
2N4401 or similar (2N3904, 2N2222) NPN transistor
Three 1N4148 diodes
Three red LEDs (must be red)
5 K ohm log taper pot
Switch
Transistor socket or similar
Two banana jacks
9 Volt battery clip
Enclosure
Knob (for pot)

Comments

[fcat1]

Very nice ! Thumbs up !

Built one following your steps, and it works like a charm, I further enhanced a little bit by tapping two wires onto a small board consists of two rows of turn pins configuration, which screw on with brass pole (insulated the copper board side), so that it could use to test normal led & superflux led as well, thank you again : )

[todell-1]

Can you clarify "rotate the 5 K pot from CCW to CW"? If the POT is turn Counter Clockwise until is stops the what should the reading be? Likewise, if the POT is turned Clockwise until it stops what should the reading be?

Thanks

[todell-1]

Sure would nice to see this on a breadboard. Compairing your photo's to schematic is quite a challenge for us newbies.

[lyndon94]

nice im going to make this

i was wondering if you could test laser diodes

[NarNar]

Congrats, you got the thumbs up from Goodhart!
I'm going to try this once I manage to get 3x 1N4148 diodes and a transistor socket, whatever that is.

[Goodhart]

Very nice. I really like this.