Display driver

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JS
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Display driver

Post by JS » Sun Dec 04, 2005 5:00 pm

Is there anyone with info about a 5x8 dot matrix LED character generator or driver chip. All of the sites I've checked so far only cover the 5x7's. I got the displays for free and don't want to gang up a bunch of gating chips to make them work. The readout will only be six characters wide. Thanks JS.

JPKNHTP
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Re: Display driver

Post by JPKNHTP » Sun Dec 04, 2005 7:21 pm

-JPKNHTP
-God Bless

Gorgon
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Re: Display driver

Post by Gorgon » Mon Dec 05, 2005 2:56 am

Hi,
you only need 5 shift registers. 1 for the rows and 4(8x4) for the columns. I suppose your displays are 5 columns each. To drive these you only need 3 signals. Data, clock and strobe/latch. 74hc4094 is usable for this. You would need 30 transistors & resistors too, one set for each column.
If you split the serial datainterface in two separate systems(2 clocks) one for the horizontal and one for the vertical, you may save a lot of processing power used. You then single step the column register and load the row register with 8 shifts. Data and strobe are the same for both.

TOK ;)
Gorgon the Caretaker - Character in a childrens TV-show from 1968. ;)

JS
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Re: Display driver

Post by JS » Mon Dec 05, 2005 9:00 am

Yes, I think I see where your going with this and with some refresh reading on digital logic this is making a little more sense. I only need to generate 8 different letters (not all at once) and 0-9. I did find a site with several drivers for 5x8's but the data sheets weren't ready yet.JS

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philba
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Re: Display driver

Post by philba » Mon Dec 05, 2005 11:10 am

as usual, gorgon comes up with a good solution.

If your microcontroller has SPI, you can use that. I like the 74HC595 SR myself.

For the transistors, take a look at the uln2801 8 darlington array - nice compact package that is easy to layout in a circuit. mouser has them for $.56 and sometimes I see them even cheaper at the surplus sites. I'd be tempted to use resistor networks too, just to make it a clean implementation. KOA has some reasonably priced networks if you don't mind SMDs.

Gorgon
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Re: Display driver

Post by Gorgon » Mon Dec 05, 2005 12:02 pm

Hi Philba,
I would recommend uln2803(a) for 5V logic. 2801 has no serial resistor on the inputs.

JS
I'm sorry, I didn't explicit write about refresh and such drudgery :) I more or less took it for granted since it was a matrix display. My fault.

TOK ;)
Gorgon the Caretaker - Character in a childrens TV-show from 1968. ;)

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philba
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Re: Display driver

Post by philba » Wed Dec 07, 2005 11:56 am

Hi Gorgon, you are right, better solution. In fact, I wanted to use it on a board I am making. It would have saved me some space but I was suprised to find that the 2803A does not appear to be made in an SMD version.

Phil

Engineer1138
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Re: Display driver

Post by Engineer1138 » Wed Dec 07, 2005 3:08 pm

philba: TI makes a SOIC version. http://focus.ti.com/lit/ds/symlink/uln2803a.pdf

It's available at DigiKey. One of the nice things about living in Minnesota is I can get next-day service from DigiKey for the price of Ground shipment :-)


I did check Micrel first: they just saved my bacon by also second-sourcing some Allegro parts that I couldn't find in small quantities elsewhere, but Micrel doesn't have the 2803 as far as I can see.

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philba
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Re: Display driver

Post by philba » Wed Dec 07, 2005 5:12 pm

Thanks, I found the ST ULN2003A (7 darlington version with 2.7K base resistor) that does come in SOIC. I try to stick with Mouser and they don't carry much TI (Linear or Freescale, sigh).

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