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widower · 09-15-2005, 04:03 PM

BTW: To calculate the resistor value:

lpt datapins are usually 0-5V
A = LED on Voltage
I = LED on current

resistorInOhms = (5-A)/I

so if A=3Volts and I=15ma

resistor = (5-3)/.015

which is 133Ohms. You can always start with a larger resistor if you aren't sure of the led specs. Say 512ohms and then reduce it until the brightness looks good. Don't exceed the LED forward biased current.

09-15-2005, 04:03 PM	#11
widower Low Bitrate Join Date: Jun 2005 Posts: 85	BTW: To calculate the resistor value: lpt datapins are usually 0-5V A = LED on Voltage I = LED on current resistorInOhms = (5-A)/I so if A=3Volts and I=15ma resistor = (5-3)/.015 which is 133Ohms. You can always start with a larger resistor if you aren't sure of the led specs. Say 512ohms and then reduce it until the brightness looks good. Don't exceed the LED forward biased current.