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### Topic: 8x8 LED matrix - all LEDS on (Read 559 times)previous topic - next topic

#### mikeruss

##### May 07, 2014, 08:24 pm

I am trying to connect a dual color LED Matrix to my Uno. Have followed the instructions and using the code from a book.
The matrix is a YSM-1288CR3G2C2

the circuit uses 8 one K resistors, and 12 Uno pins, only using Red. (No shift register)

I know its difficult without seeing what I have done, but the odd thing is that all the LEDs are on all the time. I could understand if it didnt work at all, or the wrong LEDs were lit !

The code is supposed to produce a smiley face, and have tried another one which should scroll text, with the same result.

Have checked all the connections several times.
Any suggestions what I am doing wrong ?
thanks .. Mike

#1
##### May 07, 2014, 10:34 pm
Sounds like your multiplexing could be hosed.
Or your connections. 12 pins is not nearly enough - need 8 pins for common anodes, then 16 more for cathodes (or vivce versa - 16 for anodes, and 8 for cathodes).
Or 8/8 for just 1 color.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### mikeruss

#2
##### May 07, 2014, 11:27 pm
sorry my explanation is wrong - it is using 16 pins for 1 color.

you are going to have to explain the multiplexing issue - what is it and what do I do about it ?

#3
##### May 08, 2014, 07:03 am
First, get yourself a ULN2803. Connect one output each to the common cathodes. Connect the Common to the Arduino Gnd.
The Arduino will connect to the anodes via current limit resistors.
The Arduino will connect to the ULN2803 inputs.
You drive a pattern for column 1 on the anodes, and drive common cathode 1 on for 2ms.
You drive a pattern for column 2 on the anodes, and drive common cathode 2 on for 2ms.
Repeat for columns 3-4-5-6-7-8.
That is multiplexing. The eye/brain is tricked into thinking all 8 columns are on together.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

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