4 digit LCD or LED display
in [Design]
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From: slebetman@yahoo.com on 22 Feb 2006 00:28 wrongaddress(a)att.net wrote: > > You could use a CD4511 BCD to 7 segment latch decoder driver, you would > > need 4 of them and at least 6 I/O lines (assuming external demux) or > > the TIL311 display with latch $$ > > Yes, but I have to drive 8 digits and don't want to add 8 chips. I > thought there might be a 7 segment LED digit with the latch/decoder > built in, or a group of 4 with the same. That would make it easy. > > I can't do it with multiplexing since the duty cycle would be 8 to 1 > and the display wouldn't be very bright. If you're just worried about chip count why not just use 4 chips instead of 8 and get a duty cycle of 2 to 1? Or 2 chips to get a duty cycle of 4 to 1? I've implemented scrolling LED displays that have duty cycles of 64 to 1 (64 columns x 8 rows) that is bright enough to be seen in daylight with appropriate filtering. A single chip solution will have more than 64 pins so it is going to be a big chip. Such chips tend to be smt. I don't know of any single chip solution that will drive 8 LEDs so going single chip probably requires an FPGA or PLD.
From: DJ Delorie on 22 Feb 2006 00:38 wrongaddress(a)att.net writes: > Yes, but I have to drive 8 digits and don't want to add 8 chips. Or one PIC with 16 I/O pins for the LEDs and some interface for your use. Program it to do the decoding and refresh, and any other smart logic you want (blinking?) The R8C/13 MCU, for example, is $5 and can do all that, with a clocked or async serial interface. Or get a bigger chip and program a parallel interface. > I thought there might be a 7 segment LED digit with the > latch/decoder built in, or a group of 4 with the same. That would > make it easy. Avago makes such things, but they're not cheap. > I can't do it with multiplexing since the duty cycle would be 8 to 1 > and the display wouldn't be very bright. Why not? That's what everyone else does. Just boost the current (some) to compensate.
From: DJ Delorie on 22 Feb 2006 01:34 wrongaddress(a)att.net writes: > I'm looking for a 4 digit LCD or LED display to use with a PIC > processor. Something easy to use that will latch 4 bit data from the > processor to each of 4 (7 segment) digits. More things to try: 8x1 LCD: http://www.azdisplays.com/prod/c0801a.php 8x2 LCD: http://www.azdisplays.com/prod/c0802c.php
From: John Fields on 22 Feb 2006 08:19 On 21 Feb 2006 20:42:58 -0800, wrongaddress(a)att.net wrote: >> You could use a CD4511 BCD to 7 segment latch decoder driver, you would >> need 4 of them and at least 6 I/O lines (assuming external demux) or >> the TIL311 display with latch $$ > >Yes, but I have to drive 8 digits and don't want to add 8 chips. I >thought there might be a 7 segment LED digit with the latch/decoder >built in, or a group of 4 with the same. That would make it easy. > >I can't do it with multiplexing since the duty cycle would be 8 to 1 >and the display wouldn't be very bright. --- Drive the displays with 8 times the current. -- John Fields Professional Circuit Designer
From: William at MyBlueRoom on 22 Feb 2006 11:33
Quite right, forgot the 595 was shift register. I prefer charlieplexing displays in software or if I'm starved for I/O the MAX6951 www.maxim-ic.com/appnotes.cfm/appnote_number/1880 Also I hate using more ICs than I need, I'd upgrade to a larger PIC with enough I/O to do the job. The 595 would be an advantage if you don't want a display that needs refreshing (filming?), disadvantge is power consumption and only common anode displays. Bill www.myblueroom.com |