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crazycousinjim · 09-21-2004, 04:51 AM

You are not going to want to run you LEDs serially because of your voltage drop over your led's. And, generally you do not want to run multiple LEDs in parallel off one resistor, but in this I don't see too big of a problem, depending on our power requirements. With a 5V power supply you will want a voltage drop of 1.5V (Somewhere safely in the middle), so using the the Equation If = Vd / R, where If is you forward current, Vd is our voltage drop (1.5V) and R is our Resistor value. The only thing we are missing is the If, your forward current. We need that range so that we can complete the equation so if you can find that or just the part number we should be able to get you fixed up real quick. Now for the bad news. Your USB host cannot give you unlimited current. In fact, without using a USB controller chip it will only source 100mA. That is no that much when you consider that a white LED usually wants about 20mA. So you will have to use strings of 5 LEDs. However you If might be a bit lower and we might get lucky. So find that If for you LEDs and we can figure out where to go from there.

09-21-2004, 04:51 AM	#3 (permalink)
crazycousinjim Crazy Location: Copenhagen, Denmark	You are not going to want to run you LEDs serially because of your voltage drop over your led's. And, generally you do not want to run multiple LEDs in parallel off one resistor, but in this I don't see too big of a problem, depending on our power requirements. With a 5V power supply you will want a voltage drop of 1.5V (Somewhere safely in the middle), so using the the Equation If = Vd / R, where If is you forward current, Vd is our voltage drop (1.5V) and R is our Resistor value. The only thing we are missing is the If, your forward current. We need that range so that we can complete the equation so if you can find that or just the part number we should be able to get you fixed up real quick. Now for the bad news. Your USB host cannot give you unlimited current. In fact, without using a USB controller chip it will only source 100mA. That is no that much when you consider that a white LED usually wants about 20mA. So you will have to use strings of 5 LEDs. However you If might be a bit lower and we might get lucky. So find that If for you LEDs and we can figure out where to go from there.