HD44780 chip to control LED matrix display??

[haze]

Hey guys, Im a noob sorry. I have always loved electronics but never got into the programming side of things. Im hoping someone can just point me in the right direction so i can investigate more...

I have an idea. I essentially want to make a large 1x16 character display made out of LED's that can be controlled via serial port on the fly.

Using a HD44780 (or similar) is the weird thing im suggesting here i guess. Because they interface with PC so easily and there are so many plugins and programs already made for it (like winamp plugins and so forth) i thought it would be a great controller for a LED dot matrix type display. Each pixel that would have displayed on a LCD could be represented by a LED (huge number of LED's i know, i think its gonna be 600 or so)

Now.. is this even possible? Is this a stoopid way to go about it? Am i really going to far to avoid learning about programming?

thanks for your time
Mike

 

[Nigel Goodwin]

Yes, a stupid idea! - LCD and LED are completely different, you couldn't drive LED's from an HD44780.

 

[JimB]

Have a look at MM5450 and MM5451.
These chips take serial data and a clock and drive 34 outputs.
I have used a couple for 7 segment LED displays on a project a couple of years ago.
They worked well.

HD44780 - a seriously bad idea for LEDs!

JimB

 

[haze]

Heh. Thanks guys

Yeh i realise LED/LCD's are completely different and a 44780 would not take the power of driving LED's. i just thought i could use the 44780 just as a signal to turn each LED on/off and power them externally somehow.

anyways.. im off to look at these MM5450 and MM5451.

Thanks

 

[elcopart]

Look here: **broken link removed**

 

[hjames]

Neat link. Sure beats the heck out of making a custom multiplexed display controller.

BTW, 5x7 is the minimum character matrix, 5x8 is more typical, so your LED estimate is off by a factor of 2... Also, keep in mind that this thing is going to be a power hog.

 

[haze]

oooooh baby. thanks for the link elcopart!!! Did you make this ?

Im wondering how well this would handle transitions, im keep to create a graphic equaliser type output for music.

i gotta try and understand this diagram. Thanks again !

 

[justDIY]

the MAX6953 has a built in ascii character generator and is designed to control (4) 5x7 led matrices (140 leds!) with i2c input

**broken link removed**

 

[jbeng]

Using the HD66840 to control LED's would probably be possible, but would be a nightmare. It would require a large amount of decoding and LED driver chips

I agree with justDIY, the MAX6953 sounds like what the o/p needs. Hook up 4 of those to a microcontroller programmed to do the serial interface and there you have it.

I've used the MAX7219 to control dot-matrix arrays, but it requires one chip for each digit. It also doesn't have a built-in character generator. Each chip will drive an 8x8 matrix though.

...keep in mind that this thing is going to be a power hog.

My project has four 5x7 matrices and draws 600mA (nominally).

JB

 

[haze]

Whats scaring me is the prospect of writing code to control this microcontroller. I liked the hd44780 just because that side of things was sorted with the huge amounts of winamp plugins and other random stuff out there. I essentially want scrolling winamp trackname/info and a graphic EQ type output on the screen.

Is there already software written to drive these MAX chips ? or would i have to code my own plugins

I agree with justDIY, the MAX6953 sounds like what the o/p needs. Hook up 4 of those to a microcontroller programmed to do the serial interface and there you have it.
JB

 

[hjames]

I'm not sure if I agree on the difficulty of this.

Doing a custom display is one thing, but getting something that is backwards compatible the good-ol' 14 pin LCD interface and works with all the software that's already out there is just plain *neat*.

For chuckles, I pulled the glass off of a 8x2 LCD I had lying around, and all the contacts are pretty well setup. On the particular LCD I picked, the pitch is just a bit shy of standard .1", but it fits if you split apart the cable a little bit. If I had to build more than 1, a custom circuit board and reusing the zebra strips would make this really easy.

The pinout is pretty obvious- plus you can see the traces on the LCD glass itself - the column pads and the row pads are pretty distinct, 2 groups of 20 column pads and 4 groups of 4 row pads - 40x16. 16 mosfets, and a couple bus buffer chips/registers... It would be a bit tiresome, but then again considering how many LEDs you'd be wiring up...

Aside from the mild trickyness that you need to do in order to decode the drive lines, the only real gotcha is that the LCD seems to be a "1/16" duty cycle - each row would only be on 1/16'th of the time, in comparison with the dedicated chips which drive it for longer durations. Also, refresh rate seems to be ~100Hz which is okay, but not great.

 

[Nigel Goodwin]

You're forgetting how LCD's work, they run off AC not DC, so you have to change that as well, plus de-multiplexing the drive signals. It's probably easier to use a PIC to create a compatible LED driver?.

 

[hjames]

The HD44780's use a 5 resistor divider chain to generate the LCD drive voltages - doing something unwholesome to that chain gets the column signals (all 40 of them) looking like some reasonable logic signals. The row signals seem to have some duty-cycle issues (only seems possible to get them to signal for half the expected period = 1/32), but there are a couple ways of working around this... Worst case the brightness is half of the max.

There shouldn't be any demultiplexing at this point - it's all just buffering the signals. The column lines get some logic level buffers and the rows get some relatively beefy P-fets (40 LEDs @ ~50mA = 2A pulses or so.)

It's not a walk in the park, but given the choice between hardware hacking and a pretty massive software project...

 

[jbeng]

Driving the LED's might be less problem than I had originally thought (as demonstrated by the link from elcopart), but haze will still have to devise a way to communicate with the HD44780. He says he wants to use his computer's serial comm port, but the HD44780 chip is designed to receive it's data in bit-parallel format.
JB

 

[philba]

why the obsession with the 44780 interface? it's not that great. Serial input makes significantly more sense, especially for interfacing with a PC. Use a small PIC with some I/O expansion and it shouldn't be that hard. I'd look at the protocol that the various serial LCD controllers use. It doesn't look that hard.

 

[justDIY]

PC (usb or rs232) to PIC to Maxim LED display drivers (matrix or 7 segment) ... rely on built in character generator inside the maxim chips to do the heavy lifting, all the PIC will be going is translating rs232 to spi (or i2c or whatever)

 

[hjames]

http://lcdproc.omnipotent.net/

This is a driver-like piece of software which knows about a lot of different LCD interfaces - including a HD44780 on the parallel port.

Other programs can use LCDProc as an interface to the particular display - MP3 players, system monitors, etc.

Some stuff also exists on the Windows side too...
http://www.modthebox.com/lcdhowto5.shtml