LED questions

[Adamo]

What could cause an Led to 'burn out' in a pedal build? Could crossing polarity do it? Maybe connecting it to a circuit that's not properly grounded? I'm asking because I have a perfectly functioning Tonebender build but I've blown 2 leds so far------meaning they worked for a second or two then became 'dead'. Even now when the leds are not on the board I connect them to a 9V battery and get nothing. The build calls for an onboard led and an onboard led resistor. (It's the MBP silicon Tonebender build)

Thx

[bloxstompboxes]

What could cause an Led to 'burn out' in a pedal build? Could crossing polarity do it? Maybe connecting it to a circuit that's not properly grounded? I'm asking because I have a perfectly functioning Tonebender build but I've blown 2 leds so far------meaning they worked for a second or two then became 'dead'. Even now when the leds are not on the board I connect them to a 9V battery and get nothing. The build calls for an onboard led and an onboard led resistor. (It's the MBP silicon Tonebender build)

Thx

Did you use a series resistor for the LED? That would definitely explain the working LED and then dead one after a second or 2. Depending on which one you are using, 2.4k is probably a safe choice.

[Adamo]

I just used a standard 1/4 W 4k7 resistor per the build specs.

[bloxstompboxes]

Assuming you put it in series with the LED and wired the LED with proper polarity, it's possible then that the leads of the LED/resistor may be touching the chassis somewhere or even each other. Did you heatshrink or insulate the leads in some way? A pic  of the board and wiring, and a schematic would be good too.

[PRR]

At 9V, a backward LED won't light but also will not die.

That assumes you DO have the series resistor. 2K, 5K, 20K.... it's all good. 330 Ohms is rather small, 100K may not be enuff to light; not very critical.

Even when checking across a battery you MUST have a resistor. 9V across a 2V or 3V LED is "infinite" current and instant death.

[antonis]

9V across a 2V or 3V LED is "infinite" current and instant death.

The more "instant" the more fancy...

[deadastronaut]

there's this way...

https://www.youtube.com/watch?v=MuhUIem8dCc

or this..

https://www.youtube.com/watch?annotation_id=annotation_836905&feature=iv&src_vid=pTrlSrXkW6w&v=qJNc0is9rDs

[Adamo]

At 9V, a backward LED won't light but also will not die.

That assumes you DO have the series resistor. 2K, 5K, 20K.... it's all good. 330 Ohms is rather small, 100K may not be enuff to light; not very critical.

Even when checking across a battery you MUST have a resistor. 9V across a 2V or 3V LED is "infinite" current and instant death.

If I wanted to test my leds with a 9V battery how much resistance should I use? And, I'm assuming the resistor should be between the '+' terminal of 9V and '+' leg of led, correct?

[R.G.]

1K is handy.

1K and a 9V battery will light almost any standard 5mm or 3mm LED safely. In fact, a 9V battery with a resistor in series with its (+) terminal is a great LED tester. If you touch the LED to battery (-) and the resistor the right way, it glows safely. If you touch it the wrong way, it doesn't light.

Note that LEDs do not like to be presented with too much reverse voltage, but in general a 9V and a 1K will be pretty safe for the "standard" kind of LEDs you're likely to find.