Michael Lapson wrote: > Fred, > Last summer I made a 7-seg clock once with a C84. I used 7 pins for the > segments and three to choose digits. I reliably scanned the digits with a > 3-to-8 demultiplexer (74HCT138) The decoder didn't require any timing code, > and its fast enough that you can't see any flicker. I don't think i used any > transistors. all the current came out of the 74HCT138. > Mine used 11 pins on the PIC to address 8 digits, but I was able to spell > out stuff on the display other than numbers. If I had used a BCD to 7-seg I > could have trimmed it down to 7 pins. > > -Mike Lapson > > > Fredrik Selin wrote: > > >Subject: [PIC]: 4 x 7-segment LED with only 8 free ports on a 16F84 > > > >Hi everyone!! > > > >I4m building a clock using four 7-segment LED displays and I4ve got >only > >PORTB > >(8 ports) aviable for the displays. Any ideas how to control the > > >displays??? Use an external latch (HC574) to capture your 7 segment data with the rising edge of the 8th bit and then enable the HC138 with the falling edge (using some common bits for both 7 segment and mux address). This gets you 8 x 7S display with no ghosting. It gives you more flexibility for characters than using a 4 to 7 segment decoder chip. Can you even -get- BCD to 7SD chips anymore? Remember that you can 'strobe' your LED's with a much higher current (like 1 amp), for a low duty cycle, to make them appear -much- brighter since our eyes work as 'peak' detectors. At very high ratios I recommend using a non retriggerable monostable for the strobe so that a processor failure doesn't fry your display. Robert -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu