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Author Topic: $50 robot LED broken, anyone?  (Read 2680 times)

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Offline AdminTopic starter

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$50 robot LED broken, anyone?
« on: April 22, 2007, 09:33:26 AM »
Strangely my LED on my $50 robot has stopped working again, and I really dont know why this time . . .

Has anyone else had this problem?

My best guess is that either my resistor value is too low and it burned out, or I just have really bad luck with faulty LED's (very unlikely).

Offline jsmoker

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Re: $50 robot LED broken, anyone?
« Reply #1 on: April 23, 2007, 08:53:10 AM »
I'm not sure how your resitor is connected with the LED, but it might be the resistor value.  Try charging the battery and seeing if it starts working again.  Since the regulator isn't a LDO, the voltage may be varying with the 6V battery and dropping out of the range of the LEDs activation voltage...there also the option of touching a known working LED to the leads of your LED and seeing if it turns on.

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Offline trigger

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Re: $50 robot LED broken, anyone?
« Reply #2 on: April 23, 2007, 11:16:55 PM »
I'm not sure how your resitor is connected with the LED, but it might be the resistor value.  Try charging the battery and seeing if it starts working again.  Since the regulator isn't a LDO, the voltage may be varying with the 6V battery and dropping out of the range of the LEDs activation voltage...there also the option of touching a known working LED to the leads of your LED and seeing if it turns on.

-JSmoker

There's no way your resistor is too small.  The datasheet says it has a max continuous current of 40mA, so that's like a 125 ohm resistor @ 5V (living on the edge), so you've got plenty of margin.  And yes, the 7805 won't regulate anything below 7 volts input, but it won't let anything go higher than 5 volts either (within tolerances).  Even if it was passing all your voltage (probably about 6.9 volts at max battery), a 169 ohm resistor would (barely) do the trick.  Conclusion--crappy LED. 
There are 10 kinds of people in this world: those who can read binary, and those who can't.

 


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