Rainbowduino V3 LED Problem

Using Arduino LEDs and Multiplexing
1

I just ordered a rainbowduino V3. I want to make a big 8x8 led wall. But the documentation of the rainbowduino v3 is not clear enough for me. This is the online information Seeedstudio provides.

Provides 2 x 16 pin header for connecting multiplexed LEDs
Constant current(20.8mA) LEDs driver.
Can drive 4x4x4 RGB LED Cube or 8x8 RGB LED Matrix (i.e 192 LED)
Built in USB to UART chip (FT232RL)
Built in 5V / 1 Ampere voltage regulator
Can be driven directly via USB cable (No external power adapter needed)

Link to website: Rainbowduino v3.0 | Seeed Studio Wiki

So I'm confused my led's are superflux RGB CA

So you need 20mA and 2-3,6 Volts/color to feed them. But they are in series with 8. So you need 160 mA ? and the constant current of the output on rainbowduinoV3 is only 20 mA. I'm also confused not using resistors? Like in many projects with the rainbowduino v2.

Could someone give me some information about these things? :smiley:

Thanks

2

What I gather from their wiki is that it can only feed 5V maximum to the LEDs - without doing any hardware modifications. There is a solder bridge on the backside that allows to switch between 5V (default) and Vin (up to 9V), but I suspect that will lead to other problems (p-mosfets not turning off...)

Driving 8 LEDs in series won't work.

3

But they are in series with 8.

No they are not.

8 LEDs can be on at any one time so the peak current is 20 * 8 * 3 = 480mA
Which is lucky because the most you can get from a USB power lead is 500mA.

Built in 5V / 1 Ampere voltage regulator

This is only used when you power the board externally, that is not from the USB lead.

4

Grumpy_Mike:

But they are in series with 8.

No they are not.

If I understand this correctly, they are not in series because the rainbowduino is multiplexing (setting values) in rows?

5

Not quite. It lights up all 8 LEDs in a row, these are in parallel. It then proceeds to switch the row that is lit up. This is called multiplexing.
See this for how it works:-
http://www.thebox.myzen.co.uk/Workshop/LED_Matrix.html