how to connect and program LED display

[john2007]

Hello.

Is there any schematisc on how to connect LED display ?

In my case i want to show numbers and letters on that display and this numbers and letters should be viewable from 4 meters.

I dont know how many led's would i have to use but i guess it will be more then 300.

a.) How to connect this led board to 12F675 ( and is this possible )?
b.) How to program this on the way that i can display letters, numbers and possible images ?

John

[Ttelmah]

Ouch.....
Start at the beginning. There are two basic 'types' of LED display system. The first, is the classic 'seven segment' (really eight, if you have a decimal point), which is commonly used on calculators etc.. Text (somewhat distorted), and numbers, Just eight LED's to drive per digit. The second is the 'dot matrix' type display (normally 5*7 per character). On these, 35 LED's for each character. Then you have expanded versions of these, with multiples joined together. Now, if you had ten digits using this format, you'd have 350 LED's. Because of the number of connections this would involve, 'multiplexing' is used. So (typically), only one column at a time is 'lit', and the processsor scans rapidly through them, updating what is displayed. Now, using the 5*7 *10 matrix like this, would give 7 'rows', and 50 'columns' to connect. Since any possible pattern must be generatable on the 'rows', really seven separate connections for these are needed to the processor. This rather rules out really tiny chips like the 12F675, which only has five output connections. Also, assuming each column is held as a byte in the processor, 50 bytes of RAM would be needed, with no space then for anything else. Realistically, if the display is to be updated, without long delays, at least two complete memory buffers hould exist, so a chip with rather more RAM is needed.
Get the data sheet for the Maxim 6952, and 53.
Now, the number of connections, can be solved by chips like these (they only need a synchronous serial connection back to the processor, but you will need a significantly larger RAM area to cope with generating the display required.
This is going to be a relatively 'large' project, involving a lot of IC's, and a lot of code. If you want to try it as an experiment, then be prepared for quite a few _weeks of work. However if you only want to generate a display, then instead consider buying one of the off the shelf modules that does this under RS232 control. These are available generally, for less than the cost to build them 'one off'. Things like the AphaVision 'Window' display, often come up on ebay, for less than the cost of the LEDs included in them....

Best Wishes

[john2007]

Thank you !
Do you know where can i find schematics for such things ?

This could be the first step because i have choose to take 35 or less for each character, so i can make some test before i try with the main thing
John

[Ken Johnson]

Look at this site - I've used these signs on a serial link.

Pricey, but the hard work is all done, ready to go.

Ken