switch the brightness of an LED

If you're using a uC to turn the LEDs on and off, can you just use PWM at 10% duty cycle? Hook the photocell to one of the uC's ADC inputs.

Already run out of I/Os (and code space)

bye.

Maybe try a phototransistor.. D from BC

Buy a bigger micro.

DJ Delorie wrote:

bgennette@ >Already run out of I/Os (and code space)

The *bigger uC* idea sounds apt.

Alternately:

I have 1 ADC input and 1 LED output (PWMed) in less than 2K (out of a

I have 1 ADC input and 1 LED output (PWMed) in less than 2K (out of a

This would work better.

Set RA for minimum LED current and RA//RB for maximum LED current.

-o-----o-------o----o---- | | | | .-. .-. .-. .-. LDR | | | | RB | | | | RA | | | | | | | | '-' '-' '-' '-' | | | | | o--+ | | | | | | | | |/ | |< | o---| +--| | | |> |\\ | | | | | .-. .-. +----o | | | | | | | | | V LED '-' '-' - | | | --o-----o------------o----

(created by AACircuit v1.28.6 beta 04/19/05

forget resistors to do this stuff... use PWM to make them *appear* to be dim... your LDR idea is not the way to go - you have lights on,use this to signal to a PIC or similar to switch them

Why not hook into the lights circuit? Thats way you will know if it is dark without a sensor ! PWM an LED from a simple micro.

How about paralleling a CDs cell across R1? Set the R1 value for night time luminosity.

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

void _-void-_ in the obvious place

here's another way.

// LED input ---------->|----. | park lights ----[R1]--+ | 0V ----[R2]--' that may look screwy on your screen, use a fixed pitch font. I've never seen a LED damaged by being reverse biased at a low voltage (as may be possible with this circuit) but if you're worried add a diode in series with the LED.

Bye. Jasen