Don't know what LED's to buy.

[audiomobster]

I don't know what LED's to buy. Which voltage have they got to have for my MBSEQ-V3?

Thanks

[Wilba]

Short answer: Any LEDs will work, but aim to get 3mm diffused LEDs with reasonable brightness levels (i.e. you typically don't need any more than 100 mcd brightness, and LEDs in the 1000-10000 mcd range are way too bright and will require higher resistors on the DOUT module. LEDs described as high efficiency are good. Also, pay attention to view angle - 60° to 90° is ideal. Basically avoid small view angle waterclear ultrabright LEDs and stick with typical diffused LEDs.

Long answer: LEDs don't have a "voltage". They have a forward voltage drop, because LEDs are diodes and thus the voltage will drop between the anode and cathode. What voltage is left over, so to speak, is then what you use to determine what value of current limiting resistor to use. i.e. a typical red LED has a voltage drop of 1.7V, when powered by a MIDIbox DOUT module output pin of 5V, this leaves 3.3V through the resistor. If you use the default resistor on a DOUT module (220 Ohms), then Ohm's Law can be used to find the max current that can pass through the resistor and thus also through the LED. I=V/R -> I=3.3/220 -> 0.015 amp = 15 mA. LEDs with a higher forward voltage drop will still work, but if you use the same resistor, then the max current will be less. Note 15mA is a maximum current - i.e. if you connected the LED directly to 5V - the 74HC595 in the DOUT module has its own maximum current output which may be less.

Here's more info on the topic:

http://www.kpsec.freeuk.com/components/led.htm