First of all, thanks for all the help in the past on other projects. I am building a unit that must be powered by batteries. The thought is to use 3V camera batteries. The unit is desired to run for months on one battery set. The unit passes a beam of light through a clear plastic tube. When the material inside the tube blocks the light, a 3 volt relay is activated momentarily. The relay requires 1 amp. Because of the material being sensed, the beam must be in the visible range. Right now a CdS cell is being used. The CdS cell is slow. (response is around 10 milliseconds) It looks like the LED could be a major power sucker. I am trying out the idea of charging a capacitor and dumping it across the LED. The sample rate is 3 times per second. For each sample, the idea is to turn on the PIC, the CdS circuitry, pulse the L ED, read the resistance of the CdS cell, maybe do some calibration, determine if the rela y should be pulsed. the relay will only be pulsed a maximum of 5 times per day. Then turn everythin g off. Questions 1) What could be used to economically switch power to the relay? 2) Is 3 volts going to work as the supply voltage (especially since the voltage will decline as the battery is discharged) Would a higher voltage be be tter? 3) Is there a clever way to reduce the on-time of the LED? If I had a faster sensor (in the visible range), I could shorten the LED on time. Is there a low power source-sensor pair for visible light? Clever ideas on reducing the power required for sensing? 4) Any cool suggestions on power management? Thanks in advance Gus Calabrese -- Y2K The biggest block party on the planet http://www.frii.com/~wft/Y2K.html Let's party ! ! ! ! ! Gus Calabrese Lola Montes WFT Electronics 4337 Raleigh Street Denver, CO 80212 303 964-9670......voicemail mailto:wft@frii.com http://www.frii.com/~wft Alternate: 791 High Street Estes Park, CO 80517 if no success with wft@frii.com, try .... mailto:wft@bigfoot.com then mailto:wft@eudoramail.com