douglaswilliams said:
or maybe using multiple LEDs in a row as a bar graph, that would be great.
Hi Douglas,
Yep, that's the general idea. That's really all a prepackaged LED bar graph is anyway. Some might have some other support stuff built in but you can get, say, just a bar of 10 LEDs which looks nice and professional. Some will have the first few LEDs green, the next couple of LEDs yellow, and the top one or two red, like you might see on an audio meter.
First you might make up a simple light detector with one BJT to make sure you've got that bit down. This will give an output roughly proportional to the light detected. I made one a week or two ago while messing around in which I used an LED to show the detected light level: it would fade on as input light increased and fade out again as input light decreased.
Then you can take that output voltage, amplify it if required, and feed it to an LED bar graph. You could make your own LED bar graph from discrete LEDs, transistors, and resistors (see the right-hand portion of **broken link removed** for an example).
Take a stab at designing the individual bits and post what you get. People on this site love to help people out, but generally won't design a whole project for you unless you pay them.
It will also help if you say what kinds of circuits you've already had experience designing.
Cheers,
Torben
[Edit: Adding hysteresis or a delay like Ken mentioned will help keep the meter from jumping all over the place and give a smoother display if you find that it ends up looking too jumpy.]