Raspberry Pi 1U/3U/Stack Appliance

Intro

This thing is for making a Pi appliance mounted in a standard 19 inch server rack that holds 3 RPis in 1U configuration or 8 in 3U configuration. I was inspired by the Things referenced here to come up with something that suited my needs: Multiple RPIs mounted in a 1U space in a 19in rack, OLED management screens, Scripted service management, some basic push button controls utilising the Pi GPIO pins, Power management and modular construction to allow easy removal of an individual Pi without disrupting the others. It was this thing: https://www.thingiverse.com/thing:4300960 that started me down this path - you will note the front bar design remains almost unchanged as my design has developed! Feel free to get in touch if something isn't clear or not working properly - I'll do my best to help. The 1U/3U Rack Mount Appliance was designed, built and tested with Pi 3/3+ - all Pis with that from factor (B+, 2, 3, 3+, (not sure about 4- I don't have one) can be physically accommodated in the Pi Trays **but the GPIO PIN layouts may well be different** - so you should check the Pi Docs if you're not using the a 3/3+ and you may need to adjust either the scripted pins and/or the loom.

In designing this I wanted it to remain as flexible as possible so the dimensions were set by the size of a 19" server rack dimesions. - Chassis modules are 133x44.5MM which means that arranged horizontally they are 1U and arranged vertically they are 3U. - Both Horizontal and vertical configurations utilise an M4 threaded bar to add rigidity to the appliance. (There would also be the opportunity to use the "stacked" version as a multi pi mini tower rather than rack mounted).

Both the 3U and stacked options are future work for me but the possibility is there! I have plans to design brackets and a spacer/power module update for the 3U Appliance and an enclosure of some sort for the Stack. __Watch this space!__

1U Appliance build notes

The build is in 2 parts - the 1U chassis and power assembly and the Pi mounting Trays - The Chassis consists of a centre section and 3 Pi mounting trays plus a "Master Power switch" and 2 brackets. It all bolts together with M3 bolts but there is also provision for an M4 threaded rod to be used to further strengthen the Chassis using notches in the base of the chassis and secured at each end on the side brackets.**Don't over tighten or the chassis will arch upwards!** - The Pi Mounting Trays consist a Pi Tray, front cap and fan mount along with a front bar which allows the Pi to be pulled from the rack and reinserted. I also used the front bar to identify the pi functions by colour and sometimes by adding text to the front surface - although the model suppled here has no text. Each Pi Mounting Tray has an internal Loom for power, OLED and front panel control - which is hand built using standard connectors and splits into 2 Pieces using a JST-XH 12 Connector. For the loom and OLED setup I took my inspiration from this thing: https://www.thingiverse.com/thing:3022136 The loom and wiring set up I came up with along with the systemd service running on the pi allow the following: - on boot the pi will give information about itself - a Blue LED shows the pi is booted and has power - 2 green LEDs show the ststus of 2 other systemd services that the pi service monitors - steady green for "OK" flashing green for "Not Running" - first push button to do a clean shutdown of the PI and to start it up again from is stopped state. - Second push button to show the Pi system state - Hostname/IP address/CPU %/Temp Deg C/ Memory use and to restart the systemd service or to reboot the pi All the above relies on the attached tar file being installed and the PI being correctly set up - notes and tar file attached. **Infoscreen v2.0 Service** I developed a systemD service to run the "infoscreen v2.0" application (evolved from the infoscreen original from this thing: https://www.thingiverse.com/thing:3022136) and to monitor 2 further system services. The scripts are included in a .tgz file and will "install" when untarred. I also have a set up script that will make all the necessary adjustments to the Pi OS for this to work. Installer is intended for Raspain/debian SystemD OS To set up the Infoscreen v2.0 service save infoscreen.tgz to your Pi OS, [sudo] su to root and untar - all files have full paths so will be placed in the correct directories. There will be a file created in pi's home directory called "infoscreen-setup.sh" - you should review the content of this file before running it - it updates all system packages and adds packages needed to manage the GPIO pins and makes changes (using raspi-config) to configure the system to use i2c OLED screen. **Run it at your own risk !!** Alternatively use it as a prompt for researching and setting up the system manually There are some variables in the config file that define which systemD services will me monitored by the front LEDs - just set them to the same name that systemD knows the service by - then the LED will flash if the monitored service is not running.

Loom Assembly

The making of the loom is potentially the largest challenge if you don't have an electronics background (certainly was for me!). I'm not sure I did this in the "best" way but I used an IDC40 connector to create a "Pi Loom" connecting to Pi pins to a JST-XH 12 Pin connector (female) via a ribbon cable and all the Chassis wiring in a single loom connecting to the JST-XH 12 from the other side. I planned out the wiring in Fritzing and have included the breadboard and schematic views of the final, working version. I hope its correct (from an electrical schematic point of view) that's not really my forte!) Power is applied through pins 1 and 5 (using 2 pin JST-XM connector to connect USB cable to Pi Loom) and fan connected to pins 3 and 13 (with 2 pin JST-XH connector to allow Fan replacement) At the front of the Chassis I mounted all the switches, LEDs, OLED etc and connected all to the male JST-XH connector mounted onto a 12x4 piece of veroboard. I used the Veroboard/JST-XH Male connector as a junction box between the Loom from the Pi and the Chassis electronics. Hopefully you can see how I went a out that from the pictures. For the assembly of the LED/Switch parts of the loom I used the "legs" of the LEDs (insulated with heatshrink tubing) to make the connections rather than adding in short bits of wire. I also joined the ground wires at the earliest opportunity - i.e. only one ground wire from each side going back to the veroboard. **Note: For the LED resistors you may need to experiment to get the right value for your LEDs**

Power

For Power I used an old IBM Thinkpad PSU connected to a 4 way Buck converter via a "master Switch". The power supply connects to a socket connected directly to the switch and the switch output powers the Buck.

The Buck itself sits on the shelf to the rear of the chassis centre section and the Switch in incorporated in the Chassis as a separate module. From there I used USB charging cables to make the power leads to each Pi but cutting off the device end and adding a JST-XH connector to connect it to the Pi loom.

The power button is designed to remove power to the Buck so all your Pis stay down during assembly and you can "kill the power" for maintenance- I used a round latching push switch like this: https://www.ebay.co.uk/itm/382080260940 The wiring options are included in a separate doc - I chose Option 1

Shopping List

Per Pi Mount:

- M3 Dome head 30mm Machine Screws (low profile head) - Fan Mount - 3010 5v Fan - IDC40 connector - IDC Multi Coloured Ribbon cable (28awg) - Pi Mount - M3 nuts x 4, M3 Bolts 6mm x4 - SSD1306 128x32 (0.91in) OLED Display - JST-XH 12 Pin Connector (M&F) plus crimps x1 - Pi Loom to front Loom - JST-XH 2 Pin Connector (M&F) plus crimps x1 - Fan to Pi Loom - JST-SM 2 Min Connector (M&F) plus crimps x 1 - Power to Pi Loom - 22awg solid hook up wire assorted colours - Heatshrink tubing - USB Power cable(s) - Pi Heatsink set (optional) - Tactile Push Button Keycap x2 - Tactile push button switch (4 pin) 6x6x7mm - x2 - 3mm LEDs x 3 (I used one Blue 2 green) - Resistors 2x 22kOhm, 2 x 10kOhm

For The Rack

- M3 nuts x 12 - M3 bolts 20mm x6 - Centre Section Joint - M3 bolts 28mm x3 - Left Bracket and Power Module to Chassis - M3 bolts 12mm x3 - Right Bracket to Chassis - M4 nuts x 6 - Threaded Par ends - M4 threaded bar 1m (Cut to 2 X rack width) - M4 washers x 2 - Cable Ties 100mm - BUCK Converter 12/24v input 5v 5A output w/4 x USB ports - 18V 5A Power Supply https://www.ebay.co.uk/itm/255106758396?hash=item3b658c36fc:g:Y0oAAOSwsyxhJMmF - Laptop 19v power supply with standard connector - 12v Female DC Power Connector (CCTV Type) x1 - plug for Laptop PSU - 12v Male DC Power Connector (CCTV Type) x1 - Plug from Switch to Buck

Specialist Tools

- JST Crimping Tool - SN01BM