Hi all,
Jumping in the waters for designing things. First thing I want to do is to connect multiple accelrometers (~6-10) to one of the Arduino's and send the data remotely to RaspPi.
Planning to use ADXL345 accelerometers (could be changed, if it would make life easier), and nRF24L01 for wireless communication between Arduino and RaspPi.
I am very new to Arduino , but assuming with some effort will be able to master any Arduino complexity.
My question to the community:
Is the Arduino Uno the best option I have for this project, or should I consider other boards? Smaller the better, with less power hungry option.
What other electronics or components do I need?
Link to details of any similar project would be great.
The Uno is the best board for a beginner because most software and add-ons work with it. The Nano is similar to an Uno but on smaller board so it can't use Arduino shields.
The ADXL345 does not need an Arduino interface between it and the RasPI. The RasPI can read from it directly.
The ADXL345 supports both SPI and I2C interfaces but if you're planning on using 6 to 10 of them you're going to run out of I2C addresses; you'd need to use an I2C multiplexer (pain in the butt) or SPI. With SPI you just need 3 pins plus an extra pin for each sensor. I encourage you to read up on how SPI works.
Be aware that the ADXL345 is a 3.3V device. If you use an Arduino you'll want one that runs at 3.3V or you're going to need some type of voltage level converter(s) between it and the sensors. The RasPI has 3.3V IO so it's not a problem there. Sometimes you can find ADXL345 modules with level converters built-in -- and they solve the voltage problem nicely, of course.
Finally, your problem begs the question as to why you're using that many accelerometers. The curious here (like me) will expect you have some kind of misconception as to how accelerometers work.
You do have to be careful with what else is on the SPI bus. When the ADXL345 is de-selected, it is in I2C mode and it can misinterpret commands sent to other devices.
I have a system running now that has 4 ADXL345s on SPI and there is really no limit to how many until you run out of spare pins to drive all the select lines.
How far away are all the accelerometers? While it is possible to go more than 20ft with high speed SPI, you do need to understand a few things about transmission lines and propagation delays to make it work.
Chagrin:
I need to use Arduino as my accelerometers will be away from RaspPi, several feet. So basically, I need to keep RaspPi on my table when things are moving.
Agree, I need to learn more about I2C and SPI.
Accelreometer module I have can take voltage 4-6V, so its nice in that sense.
The reason I need more than 1 is: basically to access the relative position of different moving points. So point A, B and C all connected, but moving randomly, I need to know how much, for instance A moved relative to B etc...I assume I do not have an option not to use more than one accelerometers.
MorganS,
Seems I must go with SPI, thanks. I need to spend some time learning about it (any references for head start is really appreciated).
Accelormeters will be within 2-3 feet of each other, but they may be several feet (10 -30) away from RaspPi.
Can you please help me with some details or reference.
As I am learning more, I see there are two options: Either have a multiplexer (I think that will be harder, as I am new to this) or have configuration as shown in the link (lots of wires, I guess).