5x7 LED matrix fixed display

You'll need a processor. I'd use an 8051 family part most likely.

Oh, unless you really mean a *fixed* message in which case just connect the leds that make up the characters to some power and leave the other ones unconnected.

Graham

Here's an example circuit and firmware using an older PIC type microcontroller. Lewin used discrete LEDs but it would work fine with an LED array.

maybe a bunch of shift register connect in a circular fashion can do the job, break the connection to load the new datas, plus some counters and decoders plus some mixed gates to connect all.

but the question is :

using discrete logic you need lot of chips, using a micro you put inside the micro the 'data memory' and the all logic to do the refresh and you need only the led drivers outside the micro.

I tought that at slow speed micro almost always beat discrete logic, my pcb maker charge lot of money and a single micro is soooo small :-) !

No.

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the

Those displays are a matrix, 5+7 -> 13 pins. You need a character rom, and a lot more rubbish.

It's like you say, a job for a microcontroller. Or single leds, or just a piece of cardboard with some holes in it ;)

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I was thinking he could make a discrete matrix maybe.

I tend to the latter solution too !

Graham

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If I understand you well, you need to drive six or seven 5x7 displays. So you have to control 72 or 84 lines. Even if you combine the long side, it will be 37 or 42. Now you have several possibilities:

- You can consider it a challange to build it in logic. Not my choice and I guess you should not have posted here if it was yours.

- You can use a pretty big micro or a smaller one with additional logic. Requires a kind of development system and some programming skills.

- You can use a PLD. Same requirements as for a micro. Neither of the possibilities seems attractive as you need either big, expensive components or a lot of cheaper ones. So I advise to chop the display in smaller parts and use one micro for two or three matrices. This way you need only two or three relative cheap micros that all run the same program although with a different display list. You still need a kind of development system but it can be build cheap. Both examples, designs and software are available free on the net.

petrus bitbyter

Of course it can be done with simple logic.

Lot and LOTS of simple logic chips !!!

;-0

Lots? I think only a few.

1 - 1/6 hex ST inverter plus two passives (clock oscillator)

1 - HC4017 connected as divide by 7

7 high side drivers driven by 0..6 of 4017 (discrete or hex inverter 1/6 of ST inverter plus p-channel MOSFETs)

7 low drivers driven by 0..6 of 4017 (discrete- n-channel MOSFETs)

1 resistor per column (5 x number of characters)

1 1N4148 diode per illuminated LED

That adds up to 3 ICs, 14 MOSFETs, 1 + 5*n resistors, and from 1 to

35*n 1N4148s, plus a capacitor or two.

Best regards, Spehro Pefhany

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But there\'s no simple _way_ of doing it.

Ok, you missed it then. Tie each anode line to vcc via an appropriate resistor. Tie all cathodes to ground. Block out unwanted LEDs with felt-tip marker.

Viola!

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"Any sufficiently advanced magick is
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Ooops, Voila!

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"Any sufficiently advanced magick is
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By 'missed it' I only meant that you were damn close. I would not have seen it myself were it not for your posting.

As a 'technical improvement' on the solution, the OP could set up a 2 amp power supply an 'blow' selected LEDs like fuses. Then, the ones left would form the characters without wasting current on unwanted LEDs.

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"Any sufficiently advanced magick is
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maxim 7219 can drive 5x7 matrix displays

Simple, Cheap, easy to build. Pick two.

There is an easy way. Take a shiftregister that adresses one column per display at a time. Tie the rows to Vcc via a resistor. A clock will drive the shiftregister and all leds light up. But as you have a fixed text you can blackout all unwanted LEDs by a felt-tip or a sticker. It's not my prefered solution but it's the most simple one I can imagine. Per display you need a shiftregister and a gate to controll it. As the logic may not be able to drive the LEDs, you may need some buffers. You can use one clock to drive all shiftregisters. Even then, chipcount and boardspace are high compared to one micro/two displays. (I'm sure one micro/three displays is also possible.)

petrus bitbyter

That's what I was looking for!

Why didn't I think of that?

When I feel like changing the message it's simple too!

Thanks!

I think generating the SPI signal for the 7219 might be even more unpleasant than generating the drive signals directly.

Best regards, Spehro Pefhany

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Violins !

And sure that'll work fine. ;-)

Graham