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LED in Coin Door
SirPeale:
--- Quote from: BillyJack on June 06, 2003, 12:31:25 pm ---Well, I figured my post would be about worthless. Actually, the lights in my coin door are the same type as yours. They make some LEDs like that too, but I'm not sure they're small enough or inexpensive enough for our coin doors.
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The savings in power/bulbs alone would be worth it.
But, back to my OP...how DO I calculate for resistance?
Carsten Carlos:
I've never seen a shop mentioning forward and reverse voltage (and I'm an electronic guy) - but only the forwarding is important, typically something like 2.4V, if you don't have the superbright ones.
Have some explanations how to calculate LED's on my homepage, too - don't know about their calculator, as I calculate it on myself.
In short - calculate R=U/I
where R is the resistor you need
U is the voltage that is to much and needs to be killed - e.g. you have a 5V powersupply, but a 2.4V LED = 2.6V you want to drop
I is the current the LED draws -e.g. 20mA = 0.02A
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R=U/I
R=2.6V / 0.02A
R=130 Ohm
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Just get the nearest value available on your electronic-store, usually the next higher one.
Hope this helps.
Carsten Carlos:
--- Quote ---Also, I'm getting wildly varying values when I put in current values. When I put in 20ma, I get a resistor rating of 1590, but 50 gets me 569. How do I know what to use?
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Again, very weird shop. The idea behind - to achieve superbrightness you need 50mA - calculate with 0.05A if you wanna use the formula above.
If you don't need the full brightness the LED is capable of, you can drive it with 20mA. The LED won't live notifying longer though.
Don't know why they mention it anyway. Would be the same if you buy a lightbulb and they advertise you can use it with 70-110V.
TazMan:
--- Quote from: BillyJack on June 06, 2003, 12:15:00 pm ---This response always comes up when someone asks this question, and I know this isn't the answer you were looking for either... but have you thought about the wedge-base LED's that are available? They're already "resistorized" and run off 12-volts.
http://www.superbrightleds.com/1157.htm
I think TazMan used them in his cab and they plugged right into the sockets on his coin door.
BillyJack
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Yep, I sure did.
Peale - are the type of bulbs you're looking for bayonet based leds?
If so, SuperBrightLeds als carries those - between 1 and 2 bucks each <Click Here>
They do not mention on their site if these have any built-in limiting resistor like the wedge based bulbs do. But, I bet you could shoot them an e-mail and they could answer that. If not, I'll leave Ohm's law to the experts (Carsten, RandyT, et al) I'm just happy I haven't fried myself while playing with electricity ::)
SirPeale:
Carsten Carlos: thanks for the reply. Good info there.
Taz: Yep, bayonette style. Couldn't remember the name.