ADXL355 Data Acquisition System

Overview

This project implements a high-speed data acquisition system for three ADXL355 accelerometers using a Raspberry Pi and a host computer. The system captures acceleration data at 1000 Hz from each accelerometer and streams it to a host computer for storage and analysis.

System Architecture

1. Raspberry Pi: Acts as the data acquisition device, interfacing with three ADXL355 accelerometers via SPI and streaming data over TCP/IP.
2. Host Computer: Receives the streamed data, processes it, and stores it in binary files for further analysis.
3. ADXL355 Accelerometers: High-precision, low-noise 3-axis accelerometers.

File Structure

Raspberry Pi (192.168.0.23)

• /home/bvex/accl_c/accl_tx.c: C program for data acquisition and transmission
• /home/bvex/accl_c/accl_tx: Compiled executable of accl_tx.c
• /home/bvex/accl_c/logs/: Directory for log files

Host Computer

• accl_rx.c: C program for receiving and storing data
• accl_rx: Compiled executable of accl_rx.c
• run_accl.sh: Bash script to automate compilation and execution
• logs/: Directory for log files

Hardware Setup

Pin Connections

ADXL355 Data Acquisition System

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Hardware Setup

Pin Connections

ADXL355 Pin	Raspberry Pi Pin	Accelerometer 1 (SPI0)	Accelerometer 2 (SPI0)	Accelerometer 3 (SPI1)
MOSI	PIN 19 (SPI0 MOSI)	Connected	Connected	-
MISO	PIN 21 (SPI0 MISO)	Connected	Connected	-
SCLK	PIN 23 (SPI0 SCLK)	Connected	Connected	-
CS	PIN 24 (SPI0 CE0)	Connected	-	-
CS	PIN 26 (SPI0 CE1)	-	Connected	-
MOSI	PIN 38 (SPI1 MOSI)	-	-	Connected
MISO	PIN 25 (SPI1 MISO)	-	-	Connected
SCLK	PIN 40 (SPI1 SCLK)	-	-	Connected
CS	PIN 12 (SPI1 CE0)	-	-	Connected
VDD	3.3V	Connected	Connected	Connected
GND	GND	Connected	Connected	Connected

Note: Ensure that you connect the VDD (power) and GND (ground) pins of each accelerometer to the appropriate 3.3V and GND pins on the Raspberry Pi, respectively.

NOTE:

Raspberry pi 4 and above models have two SPI busses that can be used simultaneously. In this case since we are reading out three SPI sensors, we need to access the 2nd SPI bus on the pi called SPI1. To activate that add this line to "/boot/config.txt":

dtoverlay=spi1-3cs

Software Dependencies

Raspberry Pi

• GCC compiler
• SPI kernel module enabled

To enable SPI:

1. Run sudo raspi-config
2. Navigate to "Interfacing Options"
3. Select "SPI"
4. Choose "Yes" to enable SPI
5. Reboot the Raspberry Pi

Host Computer

• GCC compiler
• Bash shell

Installation and Setup

1. Clone this repository on both the Raspberry Pi and the host computer.

2. On the Raspberry Pi:

   cd ~/accl_c
   gcc -o accl_tx accl_tx.c -lm

3. On the host computer:

   gcc -o accl_rx accl_rx.c

4. Ensure that the run_accl.sh script has execute permissions:

   chmod +x run_accl.sh

5. Update the SSH_OPTIONS in run_accl.sh with the correct path to your private key for SSH authentication.

Usage

1. Connect the ADXL355 accelerometers to the Raspberry Pi according to the pin connection table above.

2. Ensure both the Raspberry Pi and host computer are on the same network.

3. On the host computer, run the run_accl.sh script:

   ./run_accl.sh

   This script will:

   • Compile the C programs on both the Raspberry Pi and host computer
   • Start the data acquisition program on the Raspberry Pi
   • Start the data reception program on the host computer
   • Display the elapsed time of the data acquisition process

4. To stop the data acquisition, press Ctrl+C in the terminal running run_accl.sh.

Data Output

The received data is stored in binary files in the outputs directory on the host computer. Each accelerometer's data is saved in a separate subdirectory:

• outputs/[timestamp]-accl-output/accl1/
• outputs/[timestamp]-accl-output/accl2/
• outputs/[timestamp]-accl-output/accl3/

Each subdirectory contains binary files with chunks of data, named in the format: [start_time]_chunk_[number].bin

Log Files

• Raspberry Pi: /home/bvex/accl_c/logs/[timestamp]_accl_tx.log
• Host Computer: logs/[timestamp]_accl_rx.log
• Script Log: logs/run_accl_[timestamp].log

These log files contain important information about the data acquisition process, including any errors or warnings.

Customization

• To change the sampling rate, modify the ADXL355_ODR_1000 definition in accl_tx.c.
• To adjust the acceleration range, modify the ADXL355_RANGE_2G definition in accl_tx.c.
• To change the data chunk duration, modify the CHUNK_DURATION definition in accl_rx.c.

Data Visualization and analysis

Use the provided jupyter notebook called accl_data_analysis.ipynb to plot the data from the three accelerometers.

Troubleshooting

1. Connection Issues: Ensure that the Raspberry Pi and host computer can communicate over the network. Check firewalls and network settings.

2. SPI Errors: Verify that SPI is enabled on the Raspberry Pi and that the ADXL355 accelerometers are correctly wired.

3. Permission Errors: Ensure that the user has the necessary permissions to access SPI devices and create log files.

4. Data Reception Issues: Check that the correct IP address and port are used in both accl_tx.c and accl_rx.c.

Contributors

Mayukh Bagchi