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### Topic: help with 8x8 common anode rgb matrix panel (Read 3108 times)previous topic - next topic

#### jhtran

##### Nov 10, 2012, 08:16 pm
I am trying to understand how the common anode matrix works
here is what my setup looks like in LT spice and I will be trying to simulate it and get results such as power, current, and voltage.

so the common anodes are connected to a DC voltage, in this case I used +5 volts
and the RGB pins have to have PWM on it so that it knows when to turn on/off according to the duty cycle

can someone help me clarify on that, thanks alot of reading this.

What I think:
If one row is of LEDS is turned on, so 8 LEDS = 8X3 = 24 LEDS * 20mA = 480 mA needed to supply for 1 row? since 20 mA is usually for max brightness.
Do I use P=V*I to calculate power so 5 Vdc * I = power? what about the Voltage in the PWM?

#### Hippynerd

#1
##### Nov 10, 2012, 08:38 pm
480ma@5v is the max per column, and not really PWM, its the same as all LEDs on, 0ma with all LEDs off, and somewhere in between for PWM.

I have a test rig that uses 8 RGB LEDs, and I've hooked it up to an external power supply, because that sounds like too much current for the arduino.

Your diagram doesnt include any resistors, or IC's or other helpful info, but from what I can tell, controlling RGB LEDs with PWM is going to be limited with a common cathode setup, common anode setup doesnt seem to be as limiting in driving options.
https://sites.google.com/site/rgbledcubes

#### jhtran

#2
##### Nov 10, 2012, 08:50 pm
well here is my hardware config, im just trying for a basic simulation in LT spice

im trying to simplify the panel so that I can observe voltage, current, and power waveforms.

So my question is, for a common anode matrix 8x8
do you hook up a voltage DC source at the anodes
and what do you hook up to the RGB pins.

for a simple simulation, I do not want to make the circuit from the chips im using for my project, i just want to simulate a simple 8x8 common anode matrix and understand the waveforms.

#### Grumpy_Mike

#3
##### Nov 10, 2012, 08:51 pm
Read this it will show you what you are trying to do.
http://www.thebox.myzen.co.uk/Workshop/LED_Matrix.html

Depending on how you drive it you will need to supply power for a whole row or column when you multiplex it.

Quote
so the common anodes are connected to a DC voltage, in this case I used +5 volts

No that needs to be switched as well as the cathodes. There needs to be resistors in the cathodes or you need to drive the cathodes with a constant current drive.

#### jhtran

#4
##### Nov 10, 2012, 09:15 pm
thanks for the website that helped,

since im using a common anode matrix, and will be doing row scanning

im using a PNP transistor current source, what kind of signal is coming from the arduino pin? is it just a digital High/Low (1/0) or a certain voltage

#### Grumpy_Mike

#5
##### Nov 10, 2012, 09:20 pm
Quote
s it just a digital High/Low (1/0)

Yes.

Do you want brightness control over the matrix?
If so then it is a lot more tricky.
This project of mine in effect is an 8 by 8 matrix with brightness control, but with a fancy layout.
http://www.thebox.myzen.co.uk/Hardware/Hexome.html

#### jhtran

#6
##### Nov 10, 2012, 09:22 pmLast Edit: Nov 10, 2012, 09:28 pm by jhtran Reason: 1
well im using the LED drivers TLC 5940 to do the pwm for me
and using the atmega 328P, programming it with the arduino uno.

so that should take care of the brightness/dimming?

i am just trying to simulate a basic 8x8 common anode matrix (row scan) in LTspice

trying to obtain voltage/current waveforms.

#### Grumpy_Mike

#7
##### Nov 10, 2012, 09:34 pm
Quote
so that should take care of the brightness/dimming?

Yes it will but it will have to be synchronized with the matrix scanning, it is what that project does.

Quote
i am just trying to simulate a basic 8x8 common anode matrix (row scan) in LTspice

Why?
You can just draw out what the waveforms will be.

Quote
trying to obtain voltage/current waveforms.

Nothing special about them.

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