Re: LEDs and IPac...

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: The forward voltage drop on LEDs is usually between 1.4V (IR) to 3V (Blue/white). Most visible LEDs will be somewhere between (~2V). At 5 Volts you will be fine. : LEDs are current driven, not voltage driven. You will want to choose resistors that give you close to the max sustained amperage, usually 20mA-30mA, for the brightest output. : Maybe Andy will let us know how many mA are available from standard keyboad ports minus what the i-pac is already using... and take into account if you have a keyboard chained off it needs some current also. : : You need to control two things in your lighting circuit: : : - the amount of voltage at each LED (so they are as bright as possible w/o burning them out) : : - the total current draw in the circuit ( so you don't overload the 5V supply) : : So, first I would ask Andy Warne at Ultimarc how much current can sourced from those 5V outputs. : : Then, choose resistor values to keep that current under control. Since V=IR, and V=5, then you get R = 5/I for each individual LED. Depending on how you wire it, the I's may just all add up to a total current draw. : : I'm thinking that you want to wire all the lights in parallel so you don't have problems keeping the LED's the same brightness. Since an LED is a diode, I think it consumes the standard 0.7V that a regular diode does. So, as buttons get pressed and lights go out, the remaining lights would change brightness if you had it all in series, especially if you didn't use any resistors. : : You could also consider using an inverter (a bunch of hex inverter chips or something, depending on the number of LED's you want to light). This way, you could still use the NC contacts on the buttons, but the lights would go ON as the button is pressed. The inverter outputs a high signal when the input is low, etc. These chips are like $.89 at radio shack. : : Disclaimer: It's monday morning and my brain hasn't woken up yet, so I might not know what the heck I'm talkin' about! :) : : : : : I'm building an illuminated control panel using LEDs inside Happ buttons. I just noticed that the pinout for the Ipac LED harness includes a couple +5 volt outputs and a ground connection. Would it be okay to wire additional LEDs (not tied to the caps/num lock lights) directly to these connections as a power source? Which 5v connection should I use? How many LEDs could this support? : : : Thanks

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