LED's not working?

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stbtrax
 
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Joined: Mon May 03, 2010 8:40 pm

LED's not working?

Post by stbtrax »

I think the LEDs non-functional: I
looked a them through a camera on the TV-B gone and they do not flash. I
used the diode test function on my multimeter and they register a really low
drop 0.6v @ 20mA. I also replaced one of the IR LEDs with a green LED
and it flashes properly so I know it's not the rest of the TV-B-Gone setup.

adafruit
 
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Re: LED's not working?

Post by adafruit »

could be your battery is dead? get fresh batteries

stbtrax
 
Posts: 20
Joined: Mon May 03, 2010 8:40 pm

Re: LED's not working?

Post by stbtrax »

I am using a benchtop power supply

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richms
 
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Joined: Tue Jan 20, 2009 3:05 am

Re: LED's not working?

Post by richms »

Do you get any glow on the camera when you put your meter across the LED?

stbtrax
 
Posts: 20
Joined: Mon May 03, 2010 8:40 pm

Re: LED's not working?

Post by stbtrax »

no, I am fairly certain it's the LEDs I have hooked each one of them alone up to a current limited power source and they do not work they also drop 0.6v instead of the speced 1.2 so something is wrong there. I put in a green LED into one of the IR leds slots and it does flash.

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opossum
 
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Re: LED's not working?

Post by opossum »

600 mV at low current is typical for an IR LED, they have much lower Vf than other colors. At 100 mA it will be about 900 mV and at 1A it will be about 1200 mV.

Can your power supply provide at least 5 amps?

Try a fresh set of AA alkaline batteries. There is probably nothing wrong.

uoip
 
Posts: 127
Joined: Wed Sep 23, 2009 5:48 pm

Re: LED's not working?

Post by uoip »

A couple of diagnostic suggestions:

Find a known good TV remote control and look at it with your camera as you push the buttons. If you see the light coming from the good remote, then you know your camera's good, otherwise, try a different camera. Most cell phones, video cameras, and regular digicams that use an LCD as a viewfinder should work for detecting IR. A few cameras may have a sharp enough IR filter so they block the near IR used by TV remotes.

Be aware that some "current limited" power supplies can take awhile to go into current limiting mode, and can temporarily supply more current than specified. I've burned out an LED this way, by setting the power supply to 5V, 20mA, turning it on , and connecting the LED to the leads. The open circuit behavior is to output 5V, and at least my supply will continue putting out 5V at high current for long enough to destroy an LED. I don't know how common the issue is, maybe my supply has a too-big capacitor on the output or something. Anyway I can safely test LEDs with my supply by setting it up just as before, but before connecting the LED, I put a shorting jumper across the power supply leads, forcing the supply into constant current mode. Then I connect the LED in parallel with the jumper, and finally I remove the shorting jumper. (I could also just start it at a very low voltage and slowly ramp the voltage up). This avoids exposing the LED to a current surge.

Is it possible you exposed your LEDs to too much current as you were diagnosing things? That could have blown them out.

If not exposed to excess current, LEDs are very reliable. It's very rare to see a bad one.

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