Sending 16 bit and 32 bit numbers with Arduino I2C

I’ve been using I2C a lot lately and something that keeps popping up is the need to send large numbers.  I2C normally only sends a single byte at a time so you are limited to 255 as the largest number.  This post will show you how I break large numbers apart to send them over I2C and reassemble them on the other side.

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Arduino i2c problem sending multiple bytes

I ran into a bit of a weird problem a little while back when using I2C on Arduinos.  I friend also had the problem recently so I figured maybe it was common enough that this post could help other people.  The problem occurs when you have the master request a certain number of bytes from the slave.  Except when the slave sends the bytes back, they all show up as -1 except for the last one.  Here is some example code and a workaround solution.

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ATtiny i2c Slave

I’m working on a project where I need several sensors that communicate back to a central processor.  Since I’ll have several of these sensors I need them to be cheap and the ATtiny85 jumped to mind.  The only problem is that I’ve never used i2c with the ATtiny series before.  I read dozens of “tutorials” about it from around the web and couldn’t find a nice simple example.  This is my solution.

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