Searching for 8-digit 5*7 LED matrix display driver

Hi all,

I am searching for a driver for 6-8 digits of 5x7 LED matrix displays. All I can find seems to be the 4-digit MAX6952/3 chips. Two of these would ofcourse work, but that requires a lot of space and they are not cheap either. I do not really need all the font functionality etc. As long as I can control each LED seperately, I'm OK. Another option would be a chip with only the drive transistors and current sources and do the multiplexing in SW.

Does anybody know of chips that might do the job or manufacturers that carry these things?

Or does anybody know of 30mm 5x7 displays with integrated drivers? All I have found are 5mm and 7mm, 4 or 8 digits (and with this option I need 6 digits). Preferably these displays should be available in red and blue.

TIA,

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Stef            (remove caps, dashes and .invalid from e-mail address to reply)

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Stef
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Maxim makes 8 digit display driver chips. Do a search on MAX7219 or click on the link below:

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Other chips that you may want to consider are: MAX6591, ICM7218, ICM7228, MAX7221.

Good luck on your search.

Mostafa

Reply to
Mostafa Kassem

Probably the cheapest way would be to use a string of 74HC595s as column drivers and transistors (maybe driven from a HC138 if I/O is tight) as row drivers, and use a timer interrupt task to keep them refreshed. If CPU usage or IO is tight, you could use a seperate cheap MCU, e.g. PIC as a display controller to do the refresh & character generation and send it the characters serially. A PIC16F627 at

Reply to
Mike Harrison

You may want to look here:

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Bill
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Reply to
William Meyer

are available.

drive the columns

Yes, this can work. I suppose you would drive this in a 1/5 scan ratio and limit the peak current to the '595's drive capability?

Downside is that there is no current regulation and especially with blue LED's (Vfwd ~= 3.5V) this can cause significant differences between LED's. To solve this I'd like to use current drivers. So rearranging the martrix a little and using a scan ratio of 1/14 (as does the MAX6952) and a high(er) peak current I come to this:

1 MBI5027 16 channel current sink 2 8 channel high-side driver, or 7 dual P-FET, or 14 singles 2 optionally '595's if there is not enough I/O to drive the P's --- 3-17 parts

This gives me exactly enough drivers to drive 6 digits and an extra column of 14 discrete LED's. And the already scanning P-FET's allow for easy scanning of a keypad.

But this TLC5920 also looks nice, it may decrease the part count to 2.

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Stef

are available.

drive the columns

If you use the DMOS open-drain XX595's then you can drive up to a couple hundred mA per output depending on version (40mA average per LED, probably too much). You would probably have to upgrade the p-channel transistors if you go that high (the total power dissipation of display + drivers + resistors could be as high as 20~30W.

Current can be significantly different with no visual effect. I think you'll find it's perfectly acceptable.

If your average current requirements are rather modest and don't mind a fair bit of dissipation in the semiconductors and don't mind using single-sourced parts then it indeed might be the right solution for you.

Best regards, Spehro Pefhany

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Spehro Pefhany

Ah, never thought of high current 595's, thanks.

Do you have any experience with this? I've seen some websites saying that current is important, but those where of current source manufacturers. ;-)

I've now got a qoute of under EUR 1.00 (1000+) for a 16 channel current sink. This would replace 2 high current 595's and 16 resistors. So costwise current regulation is not bad. Not even single source looks like a problem, the Allegro and Macroblock parts are pin compatible. I'll have to compare them in more detail to see if they are fully drop-in replacements.

For now I think I have enough info to select the best solution, pity the ideal single-chip solution did not pop up.

Thanks to all who replied.

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Stef

I requested 4 samples of Texas Instruments' TLC5920DL two nights ago, and I received them this afternoon. I will be playing with them as soon as the boards are returned from the pcb manufacturer. (They have to be designed yet !!)

I have nothing but praise for TI's response time.

Reply to
dmm!

TI has at least two versions with different drive current capability (and pinout, unfortunately). Single-sourced, AFAIK, but they have been around for about a decade.

Rather similar situations. I don't think it's a problem.

That sounds reasonable. What part did you get the $1.20-ish quote on? The TI parts are more like $4 USD in 100's.

Best regards, Spehro Pefhany

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Spehro Pefhany

This was a qoute for the MBI5027. This was for another project, which I am not involved in, so I don't know the exact numbers. but it was at least

1000+, maybe 5k.
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