There are a few problems that you needs to look out for: 1. You are using the PIC pin for the LED common, this will act as a shared resistor. If you light. This can cause uneven display brightness. 1 segment it be much brighter than if you light 7. ex: displaying "1" will be much brighter than "8" 2. For maximum brightness, you will want to put more current through the LED when it is on in order to make up for the fact that it is turned off 3/4 of the time. You might not get enough current with a single PIC pin sinking all the current. It is dangerous to pump too much current in for too long of periods of time. Check the datasheet for specifics on the timing and max pulsed current the LEDs can handle. recommendation: If you can, tack it onto TMR0 with a prescaler. If you are running at 4mhz, a prescaler of 8:1 will get you about 2ms. The faster you cycle through the displays the better it is for the LED when you are pulsing current and the more flicker-free the display will be. The LEDs can go very fast, so don't worry about going too fast, its really a matter of how many cycles you want to spend refreshing the display. One trick I use for freeing up pins to multiplex displays is to use a 4017. With this you can use 2 pins (clock and reset) to select 10 displays. It is pretty easy to send a quick pulse on the clock to switch to the next display. I have a 10x8 dot matrix display that works well with this trick using only 10 pins. To boost current, just add a transistor for each common line. This also helps even out the brightness. To even out the display brightness even more, you might need to use a resistor coming off of each of the output pins. ttyl, Ben On 6/8/05, Shawn Yates wrote: > > OK, so 100 times a second (every 10mS) I need to turn the light on. > > How long would you suggest I turn it on for each time? > > I have 4 digits running of the same port. If I always have one one, it > will be on for 2.5mS, then that digit will go off and the next digit > will go on. That will make each digit refresh every 10mS and be on for > 2.5mS each time. Does that sound long enough to get bright enough to > see? I hate to get a proto board made only to find out its too dim and > I have to use two ports just for LED which means a processer with more > ports and . . . . > > Shawn > > -----Original Message----- > From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf > Of Richard Prosser > Sent: Wednesday, June 08, 2005 4:13 PM > To: Microcontroller discussion list - Public. > Subject: Re: [PIC:] Flicker Free > > I'm sure someone who has done it will correct me but IIRC the minimum > frequency is about 12Hz. Early 8mm movies used to run at 16 frames/sec > as this was supposed to be above the flicker rate but they aren't > perfect. (Or was every frame shown twice - 32Hz flicker ??) TV frame > rates are 25 (or 30) frames/sec interlaced to 50 (or 60) fields per > sec. and this normally looks OK - at least until you see one beside a > 100Hz TV. > Fluro Lights also flash at 100Hz (or 120Hz depending on where you live). > > > Computer screens are not interlaced and operate from 60Hz (which does > look bad) to 100Hz plus. (75 or 85 is a typical setting I think) > > If you choose a rate close to 100Hz and the display is also illuminated > by 50Hz lighting you may get an interference effect - I'm not sure on > this one. > > I'd go for something like 85Hz - or faster. > > RP > > On 09/06/05, Shawn Yates wrote: > > > > Hopefully this is a simple one... > > > > I am using one output port on a PIC to drive the segments several > > 7-segment LED's by switching their common pin through another port. > > > > How long do I need to leave any LED on in order for it to light up and > > > be detected by the human eye? > > > > How quickly go I need to repeat that in order for the display to > > appear to be flicker-free (or very minimum flicker anyway)? > > > > Thanks. > > > > Shawn > > -- > > http://www.piclist.com PIC/SX FAQ & list archive View/change your > > membership options at http://mailman.mit.edu/mailman/listinfo/piclist > > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist