At 2:49 AM +0000 4/5/03, mate_stubb wrote:
>
>I sent a detailed explanation about this more than a half hour ago,
>so I guess the internet ate it. Too tired to reconstruct it...
It showed up off list, and seems to have turned into a discussion on
op-amp theory...
> > If I simply connect an LED between the output and ground that
>> should give me ~5ma across the LED at 5V. Another way would be to
>> tap the signal prior to the 1K resistor with another resistor going
>> to the LED. I'm thinking either of these should work.
>
>No, the LED forward bias voltage is fairly constant, and will
>interfere with the output. You need to drive the LED with a current,
>not a voltage. Hence the LED feedback loop - it's the easiest way to
>get a nice controllable isolated current that follows the output
>voltage. If you just want an on/off gate indicator, use a transistor
>and two resistors.
You're right. Well, it works, after a Sustain setting of about 4,
but it divides the output voltage. The intensity of the LED does
vary with the output voltage of the 800, as placing the LED in series
is driving the LED with a current. Regardless, I need a higher
impedance.
I wanted to try avoid using a perf board and tapping the power rails.