LED Dot-Matrix Display

Step 6 Programming

So you've made it, you've plugged the battery in, but wait, no, it's not working, or maybe you just have to program it ...

Ah that'd be a good idea. Becasue of my forthought, I have a download socket already on the PCB, so, just whack in the download cable, plug that into a serial port on your PC, get Programming Editor, and get coding!

Of course it helps if you've programmed a PICAXE before, I've had about 4 years experience so far, GCSE and AS/A level.

The first thing to do is to type:

main:goto main

This just sets up the PICAXE for the program, put the important code between the main and goto main, I do this so I don't forget to do it later. The next task is to set the outputs, which pins do you want high, and which low. The long and time consuming way is to go:

high 1high 2high 3low 1low 2low 3

Or you can be cool and set the states all in one line with:

let pins = %00001110let pins = %00000000

This works by giving each pin a specific digit, so pin 8 is the fist digit, pin 0 is the last digit and so on. We also need to be able to put a time delay in there so the pins are actually left on long enough for the LEDs to light. There are 2 main PICAXE waiting commands, wait and pause, wait 1 waits for 1 second, where as pause 1 waits for 1uSecond, which is what we need.

Those inclined to nit picking will have noticed that there are only 8 pins on the pins=%00000000 command. Yes, the ninth output on a PICAXE18X is infact the serial out pin. This requires a completely new piece of code to set.

poke $05,%00000000poke $05,%00001000

I'm not too sure why this works, or why it's nessesary, but I did get it from the friendly people at the PICAXE Forum

So putting all that together gives us:

main:			              ' Letter Alet pins = %00011000	          'poke $05,%00000000 		' Set SERTXD line lowpause 1				           'let pins = %00100101		  'poke $05,%00001000 		' Set SERTXD line highpause 1				           'let pins = %01000101		  'poke $05,%00001000 		' Set SERTXD line highpause 1				           'let pins = %10001000	          'poke $05,%00000000		' Set SERTXD line lowpause 1				           'goto main                               '

That should display the letter A on you dotmatrix display

Comments

[chinnokker999]

Hey i was wondering how you'd make a "T" with this setup... Since there's an even number of horizontal rows, you wouldn't be able to center the vertical line coming down from the top of the "T"...

[pinski1]

Ah, you've found the fatal flaw... Because of my limit on size and the number of outputs, I could only have a 4x5, not the standard 5 by 7, but it does the job, and I like it.

[thermoelectric]

Could You make another one that is 5x7?

[pinski1]

I could, but I won't. The chip I used above, the PICAXE18X doesn't have more than 9 outputs. Ideally you'd need one with 12 outputs, or some further ICs to add to the previous 9 outputs. I'm not making another one, because I really don't see the point there are other things which I'm yet to do, things with ethernet and X10.

[aklem]

Lol just use a multiplexer... and are u using the x10 firecracker?

[Ankush]

I was wondering, can you display a sinusoidal wave-form in ur 4x5 dot matrix. I know u r using it to display alphabets & numbers. But i believe that you cannot have a sine-wave on this type of display device.........as un-neccesary LEDs would glow.

[Ankush]

Well you could display a T with a 4x5 dot matrix.......just that it is the small T...."t"!!!!

[pinski1]

I'm afraid you can do neither. The resolution is far too small to display a capital T let alone sin waves. The LED's wouldn't unnecessarily glow.

[Ankush]

I actually meant small "t".....unless ur looking to display only capital alphabets. Actually if you draw the schematic diagram of your 4x5 matrix you will find that to display only a diagnol 3 LED's , unneccesary 3 other LED's would glow, try it & tell me if thats not true!!.

[pinski1]

if you read the explanation, you'd realize it's is not true... The technique is called multiplexing. it's where you switch on all the LEDs on in a column or row at once, then turn them off and move to the next row, if you do this quickly enough, they eye doesn't see these changes and instead just sees lit LEDs. Try googling multiplexing for more information.

[Ankush]

Ok, yeah thats right. But a standard 5x7 matrix has a problem with diagnol LEDs lighting up....& i mean continuosly ON. Its all because its connected that way. Maybe a circuit diagram would show you what i mean.

[chrisapalo]

Hey... That's cool. Just thinkin'... Is there a way to use this with arduino? I have 3x3 matrix that is homemade.

[Gasburner]

Just reading the buzz, and as to the "T" argument, could you not use a PICAXE 28?

[mman1506]

oh yes the picaxe cip is better but if you need you you can use a pic chip with the same pcb .picaxe chips are pic chips with bootstrap program except you'll need to redo the programmer

[salmanmufti]

hi im student of bio medical engineering and i have assigned a proj to display a counter from 0 to 9 on dot matrix through a switch means whenever i press a switch it counts and stop untill the switch is pressed next time i have to make hard ware also and by using atmel 89c51 microcontroller and 8x8 dotmatrix plz help me i have to submit it after 3 days plz give me coding and circuit diadram plzzzzzzzzz im counting on u plzzzzzz

[sammy_pic]

i could help but its going to be using a PIC microcontroller instead. and i hope your assignment is not too late at this time. My e-mail is [e-mail]