"Chopping Board" Raspberry Pi Cluster

Posted on January 10, 2022 at 18:12 by GreenFrog

Chop Board Raspberry Pi Cluster

Time has come to finally give my K3s cluster, LMDS Development Env and OMV NAS some form of unity, so they don't clutter my desk as much. As I don't have a 3D printer on hand, I had to improvise. I needed some cheap and easy to work with material that can be cut and drilled without any special tools. Normally there are only two materials that comes to mind - wood and plastic.

Cutting wood using hand tools on a kitchen table won't be particularly precised job and for small pieces also difficult to do, this is why I decided to go with plastic. I was looking for acrylic sheets but they aren't cheap for required thickens, also not easy to cut.

One day while cooking a thought came to mind - how would a plastic cheap chopping board work as a framing for the cluster rig? Not thinking to much more, went to the euro shop, or as you call them in US a dollar store and found a chopping board with right dimension. Bought also some bolts and nuts and started planing my cuts, looking if all will fit, cables, fan, SBCs etc.

One thing that I did not realise immediately, is that chopping boards are usually concaved towards the center, it make sense for chopping vegetables but created some challenge along the way. At the time I had no alternative so went with the plan anyway.

Materials
Tools
Wiring
Result

Materials

Generally idea was to make it all cheaply and reuse what I already had around the house. I wanted to create something that cannot be easily broken while moving and something that is aesthetically acceptable to be standing on my desk.

The best part of the project was to figure out what can I use to build it from, how all that should be put together and wired around? Sometimes figuring out how to reuse things that intended purpose is different than you want them to serve is more rewarding that buying all precut and fabricated for you. The down site of DIY is that all the work require time and if you don't have it then save yourself a frustration and buy something half made.

Chopping board x 1
Long cabinet bolts and nuts x 4
Plastic pipe big enough that bolt can go through
Two way rocker switch (fan speed selector)
Buck converter (power regulator that lowering voltage from 12V to about 4V allowing me to reduce fan speed making it silent.
120mm fan x 1
Raspberry Pis - 4 x RPi4 and old BananaPi M2 with SATA port
SD Cards x 4
USB cables (25cm or 50cm long) 3A power delivery capable
Gigabit Switch x 1
USB Hub x 1
Plastic standoffs
Some wires and barrel connector
Some velcro, electric shrink rubes
Network cable and RJ45 Connectors

Tools

Drill and drill bits
Metal cutting hand saw
Soldering iron and some supplies
Multimeter
RJ45 crimping tool

Raspberry Pi Cluster Build components

Wiring

Wiring is quite simple.

You need to know what is a buck converter and how to use it. In essence buck converter is a simple device that can limit voltage or current to certain values, values that you will set converter to yourself using screwdriver and measuring output with multimeter.

Remember - to high (V - Volt) voltage will burn your electronic, voltage has to be close to recommended specification of the device you want to power up. Voltage cannot be to low or to high with tolerance of about 10% - it means, if you power your Pi with 5.6V adapter rather than recommended 5.2V, it will survive but it might not survive 6.5V. This rule is always applicable to any electronic you will ever connect in your life accept motors, i.e. fan is a DC motor with blades, it will tolerate higher voltage for a while, to low voltage will slow blades down and is safe to be used that way. You will power 12V fan with 5V USB charger, it will just not spin as fast.

Another rule you need to know is that any device you power ON wil drown some amount of current (A - Amp) and your PSU - Power Supplier will always be labeled accordingly about what Voltage can deliver i.e. 12V or maybe 20V and what is the maximum current it can provide with this voltage i.e. 5A or maybe 5000mA where both these values means the same thing. Device you want to power has to consume less than max Amperage PSU can deliver at pick power. If you exceed PSU max power delivery by to much it will get hot and die, device might not even start but wont be damaged.

Sometimes label on the device do not tell how much Amps can it consume, instead it will tell you its power usage i.e. 48W = 48 Watts and require 12 Volts to operate - how can you know what PSU to use? Find PSU that deliver 12V exactly as that needs to match. To make sure PSU is strong enough we have to do simple calculation: 48W / 12V = 4A. It means if you want to power device that is rated for 48W at 12V you need PSU that provide not less than 4A or 4000mA.

Having all above in mind this is how all got connected together

AC power from the wall outlet comes into PSU that converts it to 12V and is capable to deliver 5A - this is PSU that was initially powering up an USB hub alone. I am using this PSU to power USB hub and a fan that gets +12V or +5V depending from the switch position making fan go slower or faster - simplest possible solution without going with PWM - Pulse With Modulation fan and driver for it.

Network Switch is powered with another PSU as it also provide network to my laptop etc.

Raspberry Pi Cluster Build wiring