No I am not doing a school project...
If I wanted to sense a temperature and light 4 LEDs starting at temp "x " (around 30c) and light a LED at "x or less" and 3 more in 1c incriments, leaving #4 on over x+4 what is the easiest way to do it? I an seeing a 339 and a buttload of resistors but I think I am working too hard here.
I think you can adapt one of the bar graph chips to do this.
...Jim Thompson
For N leds, you need N+1 resistors to set your trip points - set them up as a ladder.
I've seen "bar graphs" that just put the LEDs in series, each paralleled with a resistor. If you scale the input voltage right and feed it into the top of the chain of LEDs, they light up in sequence as the voltage increases.
How about an 8-pin PIC with an A/D input?
Heck, a 6 pin PIC with A/D (eg 10F220). 1 pin to sense the temp, LEDs like so:
GP1 --[R330]------------ | | | | - V - V ^ - ^ - | | | | +--+ +--+ | | GP2 GP3
All tristated = no LEDs GP1 0V you can turn on 0 or 2, GP1 5V you can turn on 1 or 3.
PIC + resistor + 4 LEDs = 6 parts!
LM3914
Your solution is probably quickest and cheapest. The quad comparator is about 10 cents, the resistors less than a penny each when doing production. If it's a one-off project, it's still superbly easy. The resistor ladder keeps resistor count and layout within reason as well.
Cool, thanks
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