Sunday, 25 February 2018

PC case notification screen, part 3 - software & installation

In the first two parts of this project, I setup a Raspberry Pi to display notifications from my desktop PCs to a small LCD which I then 3D printed mounts for to install it into the PC itself.

I originally hoped to use existing software, such as Grafana and Graphite, but although they do run on the Raspberry Pi, it was difficult to get them to behave reliably, so I ended up going for a homebrew solution.

As I alluded to in an earlier post, the data comes out of the desktop by piping output from the linux command sensors via the a USB serial port like so:

sensors > /dev/ttyUSB0 2>/dev/null

The application running on the Pi reads data from the serial port, and using a simple parser, extracts the system temperature.

This is then passed to a sketch, which draws an (admittedly rather basic) gauge, displaying the temperature.

The code is available on Github. It also contains an interface class and an example implementation of that class, this is a wrapper I made around the library to make it easier to compartmentalise the processing functionality into separate classes, with the intent of making it easier to create a modular display (so further notification modules could be added in future - system speed, email/social media notifications etc).


The two mounts are either side of the metal front panel of the case, back-to-back.
The Pi sits on the inside, and the display sits on the outside (of the metal chassis - it is covered by the actual front panel of the case).
This allows the outside of the case to remain unchanged, but the display of the LCD is bright enough to shine through the translucent panel.

When the PC is powered down, the USB port still provides power, so the Pi stays on, but the power to the display is cut. This avoids having to go through the Pi boot sequence each time, but allows the display to be shut off.

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Thursday, 22 February 2018

PC-case notification screen: Part 2, mounts and wiring

In the last post, I configured a Raspberry Pi to receive stats from my desktop PC and display them on a small LCD from a car reversing camera kit.

The next stage is to turn this into a much neater setup to integrate it into my desktop PCs case.

The Raspberry Pi quite a popular format, so there's plenty of cases on Thingiverse to choose from - no need to reinvent the wheel. I went with this tray design, as it was the easiest to adapt.

The front of my PC case has several mounting points for an array of fans, so all that was necessary was to create a way of joining the Pi Tray to them.
A simple 'X' shaped bracket in OpenSCAD is all that was needed. It would be easy enough to join this to the model for the Pi Tray, but I ended up printing them separately and gluing them together.

I used the same design as the basis of the mount for the display.
Out of the box it has it's own small stand to attach to a dashboard, with a screw pivot for tilting the display. My idea was to simply remove the stand part and use the same mounting point.

The Pi attached to it's completed mount

The mount for the screen. As you can see, it makes use of the existing stand mounts


Note: The 12V line is typically the yellow line,
it just so happens on the connector I found was non-standard.

The LCD runs of 12 volts. This is nice and easy to deal with - Molex connector straight to the power supply. This was just a case of joining the connector for the display to the Molex.

The Pi requires 5 volts, and there's 2 options on how to provide this - Also on the Molex, or via USB. There's pros and cons to both methods.
  • Going the Molex route is more straightforward - it can use the same connector as the LCD, so wiring will be neater, but on the downside, when the desktop is powered off, the power to the Pi will be cut. This runs the risk of corruption of the SD card.
  • Going the USB route means more wiring and a separate power lead, but has the advantage that my desktops motherboard still powers USB devices when powered down, therefore the Pi can remain on.
I opted to go for the USB option. There's spare USB headers on the motherboard, so I needed to make an adapter to use those.

Starting with a short USB extension cable, I removed the socket and split out the wires.

Then using a header lead pulled from an old PCs front panel, remove the header connector. Then it's just a case of matching up the pins and joining them together.

The adapter without the 3D printed cover (top),
and the finished adapter (bottom).
Each motherboard adapter can support 2 ports, so I left the remaining wires outside (just heat-shrinked for safety), so they're available if I decide to add another internal port later.

The Pi is connected to this using a console cable. This is a USB cable with 4 output pins - 5V, ground, TX and RX, and connects directly to the GPIO of the Pi.

It's not recommended to use the 5V GPIO pin for power as it lacks some of the control circuitry that the usual power socket has, but has the power is coming from a regulated USB socket, it should be fine in this case.

The console cable also takes care of the level conversion of the 5v levels to Pi-safe 3.3v, and appears to the PC as a USB-serial adapter.

Finally, all that's left is to connect the display to the Raspberry Pi. Both the display and the Pi have Composite sockets, so I removed the socket from the display and replaced it with a plug.

SCAD code for the mount
As this is really quite a niche thing I'm not going to put the files on Thingiverse, but here's the OpenSCAD code in case it's useful to anyone.

// Just comment out the one you don't want

// Couldn't be bothered to do the conversion...
function inches(x=1) = x*25.4;

module piMount() {
  difference() {
    cube([inches(4.5),inches(2.75),inches(0.125)], center=true);
    translate([inches(-2.0625),inches(-1.125),0]) { screwholes();}    
    translate([55,0,0]) {cylinder(inches(0.75),inches(0.8),inches(0.8), center=true);}    
    translate([-55,0,0]) {cylinder(inches(0.75),inches(0.8),inches(0.8), center=true);}
    translate([0,40,0]) {cylinder(inches(0.75),inches(1),inches(1), center=true);}
    translate([0,-40,0]) {cylinder(inches(0.75),inches(1),inches(1), center=true);}

module screenMount() {
  difference() {
    cube([inches(4.5),inches(2.75),inches(0.5)], center=true);
    translate([inches(-2.0625),inches(-1.125),0]) { screwholes();}    
    cube([1.125*25.4,12.7,50], center=true);
    rotate([0,90,0]) {cylinder(5*25.4,0.125*25.4,0.125*25.4,true);}

    translate([55,0,0]) {cylinder(inches(0.75),inches(0.8),inches(0.8), center=true);}    
    translate([-55,0,0]) {cylinder(inches(0.75),inches(0.8),inches(0.8), center=true);}
    translate([0,40,0]) {cylinder(inches(0.75),inches(1),inches(1), center=true);}
    translate([0,-40,0]) {cylinder(inches(0.75),inches(1),inches(1), center=true);}

module screwholes() {
  translate([inches(4.125),0,0]) {cylinder(inches(5),inches(0.125),inches(0.125),true);}
  translate([0,inches(2.25),0]) {cylinder(inches(5),inches(0.125),inches(0.125),true);}
  translate([inches(4.125),inches(2.25),0]) {cylinder(inches(5),inches(0.125),inches(0.125),true);}

The basic wrapper around the USB connector
difference() {
    cube([15,40,9], true);
    translate([0,7,0]) {cube([13,27,7], true);}
    cube([9,45,7], true);
    translate([0,0,5]) {cube([20,50,10], true);}

Wednesday, 7 February 2018

PC case notification screen

I've mentioned before how my interest in electronics spawned from PC modding.

Now that I've built a new desktop for the first time in a while, I've been keen to return to PC modding and come up with some projects for my new machine.

Thing is, these days PCs are designed much more aesthetically than the old beige boxes, and so there's a lot less that needs doing - the case I have has a large glass window, the motherboard already has some RGB LEDs built in - the graphics card even has some too.

I wanted to add some case lights - thought that might be a nice throwback project, but I noticed the motherboard already has pin headers for a 5050 LED strip. Don't get me wrong, I think it's a good thing that manufacturers are taking the initiative, but all it involved was little more than soldering some wires to a length of LED strip and plugging it in - hardly a project worth writing about.

So I thought about doing a new take on the case-front notification screen. In the past this would be a basic HD44780-type LCD that could display basic text - currently playing track, system temperature etc.
My plan is to use a small, full colour screen to fit with the more colourful style of the new desktop.

Other requirements are that as I dual boot Windows and Linux, it needs to work in both environments, so I'm aiming for minimal overhead on the computer itself.

Setting up the Raspberry Pi

In order to meet that goal, I plan for it to be a completely separate device that the PC can just pipe data to, and the device itself handle the processing and display. I started with a Raspberry Pi A and a clean install of Raspbian ("Stretch Lite"), and booted to the terminal using the serial console GPIO pins.

Getting connected & installing Java
I'll need to get the Pi connected to the internet temporarily to get everything setup and installed. I used a USB wifi adapter then edited

with the following, replacing the ssid and password as necessary.

auto lo iface lo inet loopback iface eth0 inet dhcp allow-hotplug wlan0 auto wlan0 iface wlan0 inet dhcp wpa-ssid "ssid" wpa-psk "password"

then of course started with the usual update/upgrade

sudo apt-get update sudo apt-get upgrade sudo apt-get install openjdk-8-jdk
and reboot if necessary.

The display
As the display is to be mounted in a desktop computer case, there are some rather specific requirements.
  • Size - it needs to be small enough to fit in the case
  • Power - it can't use too much, and needs to be able to be powered from the computers PSU
  • Connectivity - HDMI would probably be overkill, after all, it's for system stats and notifications, not a extra monitor, and it needs to connect to the Pi, so Composite video seems appropriate.

The display and its connections
After examining and ruling out various options - netbook screen, digital photo frame, etc. I came across some reversing camera kits on eBay. For a fairly reasonable price, these kits contain a small camera for the rear of the car, and a small display to view the video on.

It fits the bill nicely - small, composite video connection, and runs of 12v, which can be provided by the PSU. Perfect. The camera the kit includes is unnecessary for this project, but I'm sure I'll find a use for it someday.

Adding a GUI
The Raspbian 'Lite' distribution doesn't come with a GUI, so I needed to install one - I went with RPD.
This is installed with

apt-get install xserver-xorg xinit raspberrypi-ui-mods lxterminal gvfs
As the pi will be running without user interaction, it needs to be configured to automatically login to the desktop. This can be done with:

We also need it to stop going to screensaver. The easiest way to do this is to just uninstall the screensaver with apt-get remove xscreensaver.
We also need to stop the screen blanking, this can be done by adding the following lines to /home/pi/.config/lxsession/LXDE-pi/autostart
@xset s noblank 
@xset s off 
@xset -dpms
And finally we need to hide the mouse cursor:

apt-get install unclutter
Once installed, we need to add the line unclutter -idle 0 & to /etc/profile.
Setting up serial communication
The Pi will be without internet connection, so to get data from the PC to it, we'll be sending it over the GPIO pins.

Firstly, use raspi-config again to disable the serial port console, as this can interfere with the data transfer.

Then run
sudo stty -F /dev/ttyAMA0 speed 115200 cs8 -cstopb -parenb to setup the serial port.

Run the same command on the desktop - just change the /dev/ttyAMA0 part to whatever the serial port on the machine is - most likely /dev/ttyUSB0 if you're using a USB to serial adapter or Arduino. (Currently I'm using an Arduino with a 5v to 3.3v level converter, though will come up with a more permanent solution when installing the screen in the case).

Installing the software
Take the compiled jar and move it over to the Pi - I put it in /home/pi.
Create a file in /home/pi/ containing this command

cat /dev/ttyAMA0 | java -jar /home/pi/PiScreen.jar

Edit the /etc/profile and add this command to the bottom

sh /home/pi/ &
This will cause the software to run on boot, and pipe input to the serial port to the application. That's it for the Pi setup.

Setting up the desktop
The software is designed to take its input from the 'sensors' command which is part of the lx_sensors package, so install this if it's not already installed on your system.

To test the display, with it booted and running, on the desktop send the comman

  sensors > /dev/ttyUSB0

you should see the dial on the display change to show the system temperature.
Send it a couple of times with the system under different loads to see the number change.

To automate this, simply add it to cron to run at set intervals, of if you want it run more frequently, add the below to ~/.bashrc (the 5 indicates 5 second intervals, adjust as necessary)

startSensors() { while true ; do sensors > /dev/ttyUSB0 2>/dev/null & sleep 5; done } 

This will allow the sensors to be started by using the command "startSensors &" in a terminal.

The next steps will be tidying up the wiring, and mounting it in the case itself.

The UI is quite basic at the moment, but I intend to expand on it to include other stats and publish the source so that others can add their own widgets to the display.