Olin, Not to disagree with you, but according to Maxim's app note 1883 (http://www.maxim-ic.com/app-notes/index.mvp/id/1883) which, perhaps incorrectly I've always assumed was correct. Quote: An advantage of pulse drive is that the human eye behaves as a partially integrating and partially peak-reading photometer. As a result, the eye perceives rapidly pulsed light somewhere between the peak and the average brightness. This means that a low-duty-cycle, high-intensity pulse of light looks brighter than a DC signal equal to the average of the pulsed signal. An advantage of multiplexed operation, therefore, is an improvement in display intensity for a given average power consumption. If I'm wrong, I'm happy to be corrected and learn something new every day. -----Original Message----- From: Olin Lathrop [mailto:olin_piclist@embedinc.com]=20 Sent: 21 October 2010 13:48 To: Joe P. Farr Subject: Re: [PIC] Convert number to bit position Joe P. Farr wrote: > Depending on how your configure your LEDs, one advantage of=20 > multiplexing could be a power saving as only one LED's on at a time No, it doesn't work that way. To achieve the same average brightness, the single on LED has to be run at much higher current. For example, if 10mA continuous results in the desired brightness but the LED will only be on 1/4 of the time, you then need 40mA when it's on. This is actually worse than the steady case for three reasons: 1 - The higher current causes more heat losses in the LED due to its resistance. Or put another way, the voltage accross the LED will be higher at 40mA than at 10mA even if the average brightness is the same. 2 - There is a upper limit on instantaneous LED current. This imposes a lower limit on the duty cycle. 3 - You have to make sure you flash fast enough to appear steady to a human observer. ******************************************************************** Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products (978) 742-9014. Gold level PIC consultants since 2000. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .