Brads Electronic Projects Forum

Hey brad, do the LED screen leads have a specific order like first red then green and the bicolor or its the same?

bitfogav uploaded a great photo in another topic on the forum, but here it is again:



if you have a look from the bottom right, the first wire is one of the common anode connections, then the next is one of the eight red cathodes then the next is common green cathode. This repeats another seven times. To make orange, you turn both red and green on at the same time.

Make sure that you have a resistor for each of the red and green cathodes (this means sixteen in all)

In the schematic appear 8 connections on each side so that means I use the green and red cathodes only?. I mean do I use 4 of each on the decoder and the other 4 on the microcontroller?

rd1196 wrote:In the schematic appear 8 connections on each side so that means I use the green and red cathodes only?. I mean do I use 4 of each on the decoder and the other 4 on the microcontroller?

This is a bi-color display, so yes, you will only be using the GREEN and RED cathodes, but only the bottom row of RED is used - for the car.

According to the schematic (shown below), there are 8 wires (RB7-RB0) with 100 ohm resistors on them providing 5 volts. That power is multiplexed to each line so that only 1 resistor is needed.

The 8 wires coming into the matrix from the left, coming out of the 7442, connect to the GROUND side of the GREEN LEDs.

The only line utilizing the RED LEDs is the bottom and that is why there is no 7442 chip for that, just the RA3 output pin on the PIC connects to the GROUND side of the RED LEDs.

Thanks a lot, but i'm still a little confused can you send me a simple schematic where you put the 12 pins so I can see witch ones i'm using on what connection.

If you have the time It would be really helpful, but if you can't thanks anyway

What do you mean exactly by the 12 pins?

There are 24 pins total on the matrix. 8 of them are for your 8 red cathodes, 8 are for your 8 green cathodes and then 8 are for your anodes (which are connected to both red and green.)

Since the game uses all green LED's you need to connect your output of the 7442 decoder to the eight green cathode connections. so looking back at the picture the third pin from the bottom right is your very first green cathode, then you go another three to your left and that is the second green cathode, another three to your left is the third green cathode and the last one on the left is your fourth green cathode. then you go to the top of your matrix, third one from the right again and that is your fifth green cathode, then go left three pins that is your sixth green cathode, go left three again and that is your seventh green cathode and finally your eighth green cathode is the left most cathode up the top (obviously you can't see the top row of pins in the photo though)

Since we only use one row of RED LED's we only need one of the red LED cathode's connected - because we simply don't use the other seven.

Finally, you need all eight anodes because you need to be able to light up every green cathode. So these connect to your microcontroller (starting at the bottom right as your first anode and repeating the same steps for the green cathodes I.E you move across three to get to the second common anode connection etc...)

Sorry I wrote 12 pins instead of 24 my bad!!. Now I understand that was what I needed thanks a lot
Thanks Brad and Elementalrage!!

rd1196 wrote:Sorry I wrote 12 pins instead of 24 my bad!!. Now I understand that was what I needed thanks a lot
Thanks Brad and Elementalrage!!

I think you want to see what pins go where on the bi-color matrix.

Brad had it posted up top there. Going from LEFT to RIGHT: GREEN Cathode, RED Cathode, Common Anode, rinse and repeat...

I am not 100% certain which row each one of them controls, you'd have to look at your bi-color display schematic.

Im going to try and explain which pin does what on the matrix and hopefully from that it will help people with any connection problems.

The picture below is a picture of one side of the 8x8 matrix.
You will see the manufacturing codes on one side of the 8x8 matrix something like the picture above (if you obtained them from Sure Electronics)

I am starting with this because this is our starting point for the 8x8 matrix, this tells us which way the display should be positioned. So the 8x8 matrix should be positioned with the manufacturing code on the left while looking at the top of the matrix. for example the picture below:
Now we move onto which pin connection does what on the matrix, the best way I found I could explain it is by the picture below using ROWS and COLUMNS:
Starting with the picture above of the top of the matrix, on the left bottom of the matrix you see a yellow wire going to the matrix, then above that an orange and then above that a green wire and then it repeats again, yellow, orange, green and so on, the same goes for the right side of the matrix, starting at the bottom yellow, orange, green and so on.

The wire colours indicate which pin is what.

for example:
Yellow wire = POWER SUPPLY (ANODE)
Orange wire = RED CATHODE
Green wire = GREEN CATHODE

In the picture above you will also see we have ROWS on the left and COLUMNS on the bottom with the numbers 0.. 1.. 2.. 3.. to 7.. if you imagine the bottom ROW of leds of the matrix as ROW-0.. and the TOP ROW of leds as ROW-7, and then we have the COLUMNS so if you imagine the LEFTMOST column has COLUMN-0 and the RIGHTMOST column has COLUMN-7..

So the yellow wire on the bottom left of the matrix is a power supply (ANODE), this is a power supply for LEFTMOST COLUMN (COLUMN-0), the yellow wire above that is a power supply for COLUMN-1, the yellow wire above that is a power supply for COLUMN-2 and the last yellow wire on the top left is a power supply for COLUMN-3, the other side of the matrix (right side) bottom yellow wire is a power supply for COLUMN-4, next yellow one up is for COLUMN-5, then yellow one above that is for COLUMN-6 and the last top yellow wire is a power supply for COLUMN-7.

So bottom left orange wire and green wire are the CATHODES for RED and GREEN on the bottom ROW which is bottom ROW-0, the orange and green wires above that are for ROW-1, ones above that are for ROW-2 and the last orange and green wires on the top left are for ROW-3. going over to the right side of the matrix on the bottom, orange and green wires are the CATHODES for RED and GREEN leds again but these are for ROW-4, next ones up are for ROW-5 and next ones up above that are for ROW-6 and the top right orange and green wires are for ROW-7 the top ROW of leds on the matrix.

I hope this has been easy enough for anyone to understand

Just incase heres abit more help:

If we was to connect COLUMN-0 yellow wire to our power supply and ROW-0 red or green Cathode to ground then the LED on the bottom left would be ON.

if we did the same for COLUMN-7 yellow wire to power supply and ROW-7 red or green cathode to ground then the LED on the top right would be ON.

Some excellent info there guys!

These LED matrix' can be confusing and I think this thread certainly clears things up

I had allready understood but thaks anyway you have been really helpfull

Thanks a lot

I got my screen from a store called futurlec is the pin order the same or is it different?

rd1196 wrote:I got my screen from a store called futurlec is the pin order the same or is it different?

Have you got a datasheet? or a part number? so we could check it

Can you upload a photo?