James & Ili wrote:
>
> Hello,
>         I'm in the middle of designing a device that is going down into the
> deep, dark ocean. It's just a little quadrature encoder that is going
> on the end of a robotic arm to measure the revolutions of a torque
> tool. The problem I foresee is driving the LED's to really make them
> shine.

Why do you need to? All a quadrature encoder needs is enough light to be
reliably detected 2mm away by a phototransistor. 10mA should be plenty.

<snip...>
. I've pulsed some IR LED's to 2 A
> with no adverse effects therefore I assume you can drive regular RED
> LED's at something higher than rated current. Any ideas ?? All help
> is appreciated.

The human eye is sensitive to peak brightness, so you can get a better
response from a large pulsed current than a low continuous one. However,
for an encoder you need a constant light source so that the
phototransistor can detect when it is interrupted. A pulsed LED would be
useless.

If you have volts to spare consider including a constant current source
for the LED, and add some filtering if you are sharing the power supply
with other equipment. This should be more reliable than a simple
resistor. Remember that when designing for remote environments
reliability is more important than component cost. Retrieving a
submersible because a 10p (about 15 US cents) LED has failed will make
you rather unpopular.

Just my thoughts,

Keith.