I have successfully loaded overlays and tested ports using Derek Molloy's spidev_test.c. Devices spidev1.0, 1.1, 2.0 and 2.1 are working fine. Then I connected my accelerometer on pins 1, 3, 28, 29, 30, 31. I tried using the slightly modified Python code I found on *http://www.havnemark.dk/?p=148* <http://www.havnemark.dk/?p=148> *(*'*Read the ADXL345 accelerometer with Raspberry Pi, using SPI bus') *and the code is not working properly. Code will be posted below.
On the other hand, I was able to connect device on I2C port and read the data without any problem. And I think I got an idea how I2C work, and idea goes like this (correct me if I am wrong): device is connected on bus and has its address (in case of ADXL345 address of device for I2C is 0x53 or 0x1d, in my case address was 0x1d). Then you access this address to open the register. This register has 64 bytes in this case, every byte has its position going from 0x00 to 0x3f. To be able to control device we write bytes to setup the device and then we read the bytes to get data from sensor. In this case accelerations are stored in 6 bytes, in pairs of two for each axis because resolution of accelerometer is 10 or 13 bits which means we need minimum of two bytes. Consequently 6 or 3 bytes don't mean anything. And then when I have values of these bytes I can combine them, do some operations and translate these values in voltage and finally translate the voltage in acceleration. I have following questions about SPI: 1) How to read the register using the *spidev* package ( *https://github.com/doceme/py-spidev* <https://github.com/doceme/py-spidev>)? Main problem is I really don't get how the communication goes. I am familiar with concept "to read data you have to send the data" but I don't know how to make the code that would do that. In other words, how would piece of Python code that says *"Go to address XxXX and read the register values at position YxYY" *look like? 2) Using the code from question 1 - how to access the accelerometer and read the device ID which is in register positioned at 0x00? 3) How to write the data to register? In other words how would piece of Python code that says *"Go to address XxXX and write the value ZxZZ to register at position YxYY" *look like. 4) Using the code from question 3 - how to put the accelerometer in measuring mode by writing the value 0x08 to register at position 0x2d Code I used: #!/usr/bin/python # -*- coding: utf-8 -*- # Example on how to read the ADXL345 accelerometer. # Kim H. Rasmussen, 2014 import time import spidev # Setup SPI spi = spidev.SpiDev() #spi.mode = 3 <-- Important: Do not do this! Or SPI won't work as intended, or even at all. spi.open(2,0) spi.mode = 3 spi.max_speed_hz = 3500000 # Read the Device ID (should be xE5) id = spi.xfer2([128,0]) print 'Device ID (Should be 0xE5):\n'+str(hex(id[1])) + '\n' # Read the offsets xoffset = spi.xfer2([30 | 128,0]) yoffset = spi.xfer2([31 | 128,0]) zoffset = spi.xfer2([32 | 128,0]) print 'Offsets: ' print xoffset[1] print yoffset[1] print str(zoffset[1]) + "\n\nRead the ADXL345 every half second:" # Initialize the ADXL345 def initadxl345(): # Enter power saving state spi.xfer2([45, 0]) # Set data rate to 100 Hz spi.xfer2([44, 10]) # Enable full range (10 bits resolution) and +/- 16g 4 LSB spi.xfer2([49, 16]) # Enable measurement spi.xfer2([45, 8]) # Read the ADXL x-y-z axia def readadxl345(): rx = spi.xfer2([242,0,0,0,0,0,0]) # out = [rx[1] | (rx[2] << 8),rx[3] | (rx[4] << 8),rx[5] | (rx[6] << 8)] # Format x-axis if (out[0] & (1<<16 - 1 )): out[0] = out[0] - (1<<16) out[0] = out[0] * 0.004 * 9.82 # Format y-axis if (out[1] & (1<<16 - 1 )): out[1] = out[1] - (1<<16) out[1] = out[1] * 0.004 * 9.82 # Format z-axis if (out[2] & (1<<16 - 1 )): out[2] = out[2] - (1<<16) out[2] = out[2] * 0.004 * 9.82 return out # Initialize the ADXL345 accelerometer initadxl345() # Read the ADXL345 every half second timeout = 0.5 while(1): axia = readadxl345() # Print the reading print axia[0] print axia[1] print str(axia[2]) + '\n' elapsed = time.clock() current = 0 while(current < timeout): current = time.clock() - elapsed This code is not working. First problem is that line id = spi.xfer2([128,0]) returns 0xf2. If 128 is replaced with 64 I get 0x79. If 128 is replaced with 0 I get 0xe5. I cannot debug this because I don't know what exactly this line does. By answering questions above, you would help me a lot. Datasheet for ADXL345 accelerometer: *http://www.analog.com/media/en/technical-documentation/data-sheets/ADXL345.pdf <http://www.analog.com/media/en/technical-documentation/data-sheets/ADXL345.pdf>* -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/f257c916-8350-4545-88e5-50724da34108%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
