(I’m still using the expensive LIS3LV02DQ.) Analog In 4 goes to SDA, and Analog In 5 goes to SCL. I hooked up my Arduino to a handy accelerometer for testing. His library abstracts the TWI innards really nicely, so I don’t have to muck with any Atmega registers or anything of that sort. Nicholas Zambetti, who wrote the Wire library, pretty much told me it should work with no problems, and he was pretty much right.
I got a pretty good understanding of how it works but before I started coding, I noticed that there were some TWI libraries both in avrlibc and in the “Wire” library in happens to be packaged as a “sanctioned” external library for Arduino, so that was pretty much that. (There are also a couple of useful application notes available here and here.) It’s so thorough that I had to print it out. To do this, I consulted the Atmega8 specification sheet, which has a pretty thorough explanation of the protocol and the implementation details on the Atmega8. So, the next step was finding out how best to handle TWI transactions. The first step was making sure the Arduino would handle the TWI – there’s pretty much no reason it shouldn’t, because the Atmega8 certainly handles it. For some experiments, two-axes may be perfectly fine, and I’m happy to save the $11.) (I’m also looking at using a two-axis accelerometer that’s much less expensive than the three-axis one I’ve been using – $4 versus $15.
The trade-off is a little bit more complicated protocols semantics, but nothing out of control. It only uses two-wires, rather than the four required for SPI, so schematic designs and board layouts become a bit more manageable. I’m doing this partially because it would be good to know how it works, but also because it’s electrically more compact. I have been using the Arduino and Atmel microcontroller’s generally using the SPI (serial-peripheral interface), but decided to look at the two-wire (a.k.a. Subscribe to our newsletter to be the first to hear from our cultural voyeurs and time-traveling anthropologists who regularly report on the signals and artifacts they bring back from the future. Join us to our office hours to discuss design, design fiction, projects you are working on and generaly Q&A. You are browsing the archives of the Near Future Laboratory blog.
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