zapperDAQ

Data Acquisition System for the NC State Electrostatic Precipitator.

The software is intended to run on a Raspberry PI Model 4b that is interfaced with Pi-Plate DAQC2 module.

Installation (Build OS and Software From Sources)

Familiarity with Linux, the Julia language, and single board computers is assumed, especially when things go wrong. Since the DAQC2 piece is specifically created for the Raspberry Pi, the build chain relies entirely on the Pi architecture. The Pi is relatively slow and troubleshooting on a slow remote platform can be tedious.

To learn more about how the DAQ system is built, and gain more familiarity with julia, check out the concept implementation also runs on a regular x86 computer.

Preliminaries

• Setup Raspberry Pi and Pi-Plate.
• Install an image Raspian OS - 64 bit version. The install was tested with raspios_arm64-2020-08-24, but should work with subsequently released versions. The 64 bit version is needed for Julia language support. Note that the DAQC2 Pi-Plate is incompatible with Ubuntu 64 bit.
• Setup the Pi so you connect to it via ssh from your personal computer.
• Ensure that you have a local X-server installed (e.g. Xming). When connected to the pi via ssh, test it by running

xeyes

In case xeyes is not installed, install it via

sudo apt-get install xeyes

Install Julia

Download julia onto the Raspberry Pi. Use the Current stable release and Generic Linux on ARM, 64-bit (AArch64) image. The install was tested with julia-1.6. Extract the tarball and create symbolic link.

Example Installation Procedure

(File name may vary with julia release and username)

(1) Download with wget

wget https://julialang-s3.julialang.org/bin/linux/aarch64/1.6/julia-1.6.0-linux-aarch64.tar.gz

(2) Extract the files

tar xvfz julia-1.6.0-linux-aarch64.tar.gz 

(3) Create symbolic link

sudo ln -s /home/pi/julia-1.6.0/bin/julia /usr/bin/julia

(4) Test if julia runs

julia

you sould see

               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.6.0 (2021-03-24)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

julia> 

You can exit out with CTRL-D

Enable Pi-Plate

(1) Enable SPI

sudo raspi-config

INTERFACE OPTIONS -> ENABLE SPI

Reboot.

(2) Install Pi-Plate Drivers

sudo pip3 install Pi-Plates
sudo pip3 install spi

Install zapperDAQ

(1) Create a data directory

mkdir $HOME/Data

(2) Clone the source code

git clone https://github.com/mdpetters/zapperDAQ.git

(3) Change to src directory

cd zapperDAQ/src

(4) Instantiate project

julia --project -e 'using Pkg; Pkg.instantiate()' 

This only needs to be performed once.

(5) Try running the sofware

julia --project main

Note that startup is slow because julia needs to compile some things each time it is loaded. Latency can be reduced through a custom sysimage described below.

Development/Troubleshooting

Running main.jl in ther REPL will bring up the GUI and start the DAQ loop. If you want a responsive REPL while the program runs in the background, comment out the

wait(Godot)

at the end of the program or click the "Stop DAQ" button. (The program will continue to run when in REPL mode, but will terminate when called from the command line).

Precompile to reduce latency

(1) Create a large swap space by sequentiall calling the following commands.

sudo -s
dd if=/dev/zero of=/swapfile1 bs=1024 count=8290304
chown root:root /swapfile1
chmod 0600 /swapfile1
mkswap /swapfile1 
swapon /swapfile1
free -m
CTRL-D

To see if the swap space was created. It is helpful to monitor resource usage via htop in a second terminal connection. It should now show an 8 GB swap space. Run the following command in the src directory of zapperDAQ

julia --project --optimize=3 -e 'using PackageCompiler; create_sysimage([:CSV, :Colors, :DAQC2Plate, :DataFrames, :Dates, :Gtk, :InspectDR, :Lazy, :NumericIO, :Printf, :Reactive], sysimage_path="sys_daq.so", precompile_execution_file="main.jl")'

This will bring up the gui. Stop the gui with the Stop DAQ button. PackageCompiler will create a custom system image. This takes a lot of time.

Load the software with custom system image

julia -q --project --sysimage sys_daq.so main.jl 

This will bring up the gui in a few seconds.

Create a startup script daq.sh

#!/bin/bash
cd $HOME/zapperDAQ/src
julia -q --project --sysimage sys_daq.so main.jl
cd $HOME

and

chmod a+x daq.sh

Calling ./daq.sh from the command line will bring up the GUI.