Model Boat Mayhem
Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: david48 on November 07, 2016, 05:02:12 pm
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I found this web site ,some will know it .https://www.kitronik.co.uk/blog/led-resistor-value-calculator .I am on with trying to make up a fibre optic board for Fairmount Alpine . If the long leg is + is the flat on the LED - I could be wrong but I thought that if the legs are the same length the flat was + . The last batch I bought from Comp Shop ,the long leg is on the opposite side to the flat . Is it me !!!
Thank all for the help
David
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From Sparkfun website...
The longer leg, should indicate the positive, anode pin. Or, if someone’s trimmed the legs, try finding the flat edge on the LED’s outer casing. The pin nearest the flat edge will be the negative, cathode pin.
Regards
Jonathan
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It was me ,just set up a warm white with 100ohm all looking good applied power PIFPAFPUF .I will try again 19 left .
thanks Jonathan
David
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My way to remember is:
The long leg is because you need more to make a +
And the flat is a bit missing, or subtracted ... -
I expect there's a clever rhyme somewhere but I can never remember them.
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If using the correct voltage can you blow an led if you reverse the polarity ?, if not just exchange the wires until it works..
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It was me ,just set up a warm white with 100ohm all looking good applied power PIFPAFPUF .I will try again 19 left .
thanks Jonathan
David
What voltage are you using . for 12v I would go from 700 ohm to 1 k ohm
john
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It was me ,just set up a warm white with 100ohm all looking good applied power PIFPAFPUF .I will try again 19 left .
thanks Jonathan
David
Using the calculator you referenced above, for 1 'warm white' 5mm LED, on a 12v battery, it gives a resistor of 470 ohm as the preferred value, so only using a 100 ohm resistor will cause it to go "PIFPAFPUF" {-)
If only using 6v, you need a 150 ohm
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LEDs have their forward voltage drop at a range of currents to give their glow. They also have a maximum reverse voltage. Exceeding either the forward current or the reverse voltage will kill them.
If uncertain as to which leg is which, connect two in reverse parallel, connect to a suitable voltage supply through a suitable resistor. One will light. That one is how they should be wired. Since the forward voltage is always lower than the max reverse voltage, the one that didn't light up can be reconnected and reused.
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LEDs have their forward voltage drop at a range of currents to give their glow. They also have a maximum reverse voltage. Exceeding either the forward current or the reverse voltage will kill them.
If uncertain as to which leg is which, connect two in reverse parallel, connect to a suitable voltage supply through a suitable resistor. One will light. That one is how they should be wired. Since the forward voltage is always lower than the max reverse voltage, the one that didn't light up can be reconnected and reused.
Now that is a handy tip O0 :-))
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Thanks for the help and input gentlemen , it was me , No 1 I picked up the wrong resistor .No2 I failed to cut the track on the strip board where I had the resistor ,in effect track by passed the resistor ,a obvious over sight , I should have known better . Redid it all this morning all good now .
David