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Electronics => Beginners => Topic started by: RL_Tracksuit_Electro on January 01, 2020, 10:10:33 pm

Title: SMD led orientation check with multimeter?
Post by: RL_Tracksuit_Electro on January 01, 2020, 10:10:33 pm

Fast forward, using the markings on the smd led I was able to determine the cathode & anadode and everything worked.

However, when I try to use my multimeter (a cheap Tacklife) diode test setting to double-check cathod/anode, the screen never changes nor does the led light up. I tested other diodes (not leds) with that setting and it works.

I have no idea exactly what kind of leds they are. Is it "normal" that some leds can't be tested by some multimeters? I don't have any other smd leds handy, nor another multimeter.

Title: Re: SMD led orientation check with multimeter?
Post by: fcb on January 01, 2020, 10:14:48 pm

White & Blue LED's have a higher forward voltage, so your DMM might not be able to push them into conduction - so they might appear open-circuit.

Title: Re: SMD led orientation check with multimeter?
Post by: RL_Tracksuit_Electro on January 02, 2020, 01:44:41 am

Indeed they are blue, thanks!

Title: Re: SMD led orientation check with multimeter?
Post by: fcb on January 02, 2020, 01:23:18 pm

One trick I've used is to put a 1.5V cell in series with the multimeter in "diode check" mode (red lead to batt-, batt+ to DUT).  This is enough usually to light the most stubborn blue/white LED's.