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I2C Address Question

Hello !

I have decided to jump into I2C after dragging my feet for a couple years..

My question revolves around wanting to get 24+ 7 Segment LED drivers (http://www.adafruit.com/products/879#Description) on the same I2C bus..

As far as I can tell I2C (from a RasPi) supports 7 bit addresses ....  128 devices WOOHOOOO !

But this doohicky has only 3 soldering bits !  NOOOOO!  I was thinking.. hey, mebbe Adafruit decided it was just not roomy enough to have 7 sodering pads .. and if I look hard enough I can solder or short pins so that I can get all 7 bits .. 

Looking at the datasheet - (page 26) - 

I see that the chip "hardwires" the other address bits .. NOOOOOOOOO!

My questions are :

  • Is this common practice..  I've heard of "base address" fron I2C device manufacturers ..  doesn't this (like this case) whipe out a bunch of addresses ?!?!
  • Is there any way around this ?
  • Is there any slave device that is nice enough to give us all 7 bits ??!?
  • WHATS GOING ON !?!? 

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Most i2c devices have just a few addresses based off a base address. You may find some that have them all though.

Programmable things like uC have it where you can choose more adreeses.

Found this 

(gratiously lifted from here - http://forum.arduino.cc/index.php?topic=50930.0)

Which seemed like a feasible work-around .. although it does require more chips & salsa :(
and a bunch of work to get my 4 bits back Grrrrr... 

https://learn.sparkfun.com/tutorials/using-the-serial-7-segment-display It uses an arduino to address the 7 segment pins and brings out the i2c lines, plus, it gives you the ability to change the address. https://www.sparkfun.com/products/11441

I see that Maxim has an SPI 8 digit controller. Add a single line controlled shift register, http://www.edn.com/design/systems-design/4410875/One-I-O-line-drives-shift-register-with-strobe , and you can control up to 8 more sets of 8 with a single shift register and only 3 lines. :) Admittedly, more chips and salsa are required for that.

Good find .. and just a couple dollars more than Adafruits... But with an onboard ATMega328 and FTDI header...
Heh, Sparkfun's version appears a lot more "smarter"