In this section, we discuss the steps to create a single stack of Raspberry Pi. A stack is the minimum set of PIs we can turn on/off using the master. It is also a way to reduce the number of cables inside the cluster. Although we describe all the steps, we strongly recommend you to avoid some of them. In particular, you shouldn't build the custom board on your own. Instead, they can be printed by some company specialized in this task; it it will cheaper and the final product will have a better quality.


As we mentioned in the overview, it is important to reduce the number of cables needed. For this reason, we designed a custom board that powers a group of PIs – a.k.a stack.

The main function of this custom board it to distribute the power among all the PIs in the stack. In addition, a temperature sensor, a power monitor and a power controller are attached to the board. The temperature sensor and the power monitor are used to collect the local temperature of the stack. Meanwhile, the power controller is used to turn on/off the Raspberry PIs in the stack. Notice that these extra-devices cannot be accessed from any PI in the stack (a.k.a Slaves). Instead, it is accessed by the master using a I2C interface.

Finally, be aware that all stacks are sharing the same I2C interface. They appear in the bus as different devices.

A single Stack

Building the stack

Printing 3D Pieces

  • Print three pieces two support and hold the Rasps (Model).For this, you will need a 3D printer at least as large as the Ultimaker 2. Piece
  • Print short spacer to support the PCB (Model). Piece
  • Print long spacer to support the network switch (Model). For this, you will need a 3D printer at least as large as the Ultimaker 2. Piece
  • Cut a pexiglass piece to separate the Rasps and the switch (Model). To use this model you will need a laser cutter. Piece

Making the PCB

The Gerber model of this schematic can be used to print it either yourself or sending it to an online service such as PCBWay.

A single Stack

The result of printed this schematic is a PCB as the one shown in the picture below. Observe that there are no components installed. It is possible to order a PCB with the components already included but it is more expensive. Finally, The picture belows shows one side of the PCB, but in practice we must weld components on both sides.


Tips for welding: When welding the micro-usb, only weld the first and last pin. Since the other are really hard to do, it should avoid lot of trouble (short-circuits and related problems)


Now it is time to mount the stack; this is a time consuming task. Simply go to a place with space, mount each stack and test it until you get the desired result.

The first step is soldering the electrical components to the PCB. For doing that, we can use the following diagram.

A single Stack

Notice how each component has a label. Using that label you can find the right component to attach using the following table.

Name Label in PCB Quantity Farnell Ref Alternative
Capa 47uF/50V C1 2 1902931
Capa 100uF/50V C5 1 1902932
Schottky Rectifier (5V) D1 2 1697512
Schottky Rectifier (12V) D2 1 2341584
Capa 330uF/16V C3 4 9451102
Capa 1uF C7 4 1759432
Capa 100nF C8 4 1759143
Relay Re 6 1094008
Diode Standard diode symbol 7 1700871
Transistors Beside each Re 6 2283624
Micro USB P1-P6. Other side of the board 6 2554967
Capa 0.01uF C6 2 1216435
Capa 470pF C2 2 1100510
Shunt Jumper on top of on/off/a{012}/sda/scl 6 2396301
I/O expander 8bits PCF8574AN 1 1703443
Board-To-Board Connector on/off/gnd/rx/tx/a{012}/sda/scl 8 9731083
Power Connector PWR IN/OUTPUT 2 224959 *
Screw terminal PWR IN/OUTPUT 2 ? *
Wire to Board Connector 2 2215304
Inductor 330uH I2 1 2493162
Inductor 22uH I1 1 2526937
Heat Sink * Attached to each SR 3 1703172
Switching Regulator (12V/1A) SR1 1 9488073
Switching Regulator (5V/5A) SR2 2 2492170 (1)
Resistor 5.6k R3 2 1100319 (1)
Switching Regulator (5V/5A) SR2 2 2492170 (2)
Temperature Sensor * Max7500 1 2515642
Resistor 5.6k R2 5 1100319
Power Monitor * PWR Monitor 1 2496402
Shunt resistor * SR3 1 1108073
Board-To-Board Connector (GPIO) GPIO Master 1 1569232
Switching Regulator (5V/5A) SR2 1 2492170
Micro USB P1-P6. Other side of the board 6 2554967
Relay Re 6 1094008
LED L 2 2497355
Resistor 2k R1 2 2447622
USB Connector 1 2442536
Pin Header 1 1022237
Jump-Wires To connect each Pi 6 563-BC-32673 Mouser
Network Switch 1 2908341 GS608-400PES Misco

The Alternative column allows you to choose between two components ; the PCB is compatible with both prints. You have to choose between alternative (1) which is generally cheaper or alternative (2) which has less components (thus the print of R3 should be left empty).

Power connector and screw terminal should not be pluged at the same time. Moreover in the last layout, both 12V output connector share the same print, you will have to choose before soldering.

PCB with components already attached


Final assembling

To connect all the elements of the stack follow the following steps:

Step 1: Plug the master if the stack is acting as master.

Plug Master

  1. Attach the support to the PCB

  2. Plug the slaves (Raspbs)

  3. Attach the short spacers to the PCB

  4. Attach the long spacers to the PCB

  5. Put the two remaining supports on top of the Rasps

  6. Attach the pexiglass separator to the supports on top of the Rasps

  7. Attach

  8. Attach the support to the PCB


It is, of course, a good idea to test every stack before connecting them all together. The easiest way is using the power supply; if everything goes well you shall see four red leds turning on. That should be enough. Nevertheless, you can also check if each Raspberry Pi is really able to boot. This is a good idea because while booting they consume more energy. Hence, prepare four Sd Cards and power on the stack with the SD Cards inserted.

Should you detect a problem, it can be:

  1. A failure in a cable
  2. A problem with the custom board
  3. A problem with the SD Cards
  4. A problem with the Raspberry Pi
  5. Ground and Plus inverted (you will see the smoke)