Arduino -> Xbee -> MAX7219 reality check

Hi I am building a circuit and I want to verify that what I am doing can be done (and with the parts that I intend to use). I have Freeduino, that I will connect to a Xbee, the Xbee will communicate wireless to another Xbee that sends its signal to a MAX7219 to multiplex about 50 LEDs. I think that once the Xbee network is up, that I can seamlessly communicate between the Arduino and the MAX7219 with SPI.

Is that correct? Am I missing some essential steps here? I am just going for the big picture, I am capable enough to dig through the data sheets and the playground documentation to get the details working (I hope).

Your advice is much appreciated.


SPI requires two signals a clock and data. Any wireless device will only in effect give you 1 wire (though it is wireless) therefore you can't send SPI data through your system. :(

iirc, the difference between the 7219 and 7221 is the 7219 does not have an SPI interface, it uses some form of 3-wire serial.

Either way, it shouldn't be that hard to get a spare ATmega168 and program it using the arduino evironment (even sitting in your arduino board temporarily) to act as a bridge beween your xbee and 72xx chip.

Thanks for the feedback.

I now see that I will probably need to a micro controller on both sides of the wireless connection. I will do some experimentation and see what I can come up with. I am trying to keep the power consumption low because the second Xbee, the MAX7219 and the LEDs will run on batteries, but if I have to I can add a micro controller.

The ATmega168 draws 0.25mA at 1MHz, maybe a few mA at the 16MHz the Arduino uses.

A single LED typically draws 20mA, far more than the ATmega168. On a project with a 64 LED panel, the power consumption of the Arduino doesn't even factor in.

Running LEDs on batteries can be a problem though. NiMH AA batteries are good for about 2500mAh these days, so if you have 10 LEDs on at a time on average, you're using 200mA, and your batteries will be good for 10-12 hours.

Also, I'm not too familiar with xbee, but RF devices usually use quite a bit of power.

The point of all this is really that compared to the rest of your project, the power consumption of a microcontroller is almost nothing.