Building the CubeSatSim Pico

These are the instructions for building the Pico Board, Batt Board, and Solar Board.

Here is the software for the CubeSatSim Pico: https://github.com/alanbjohnston/CubeSatSim/tree/pico/cubesatsim

Pico Board v0.4

These are the instructions for building the Pico v0.4 board.

You will need these tools:

• Safety glasses (to protect eyes while soldering or trimming leads)
• Soldering iron with fine tip and very thin solder (I use lead-free solder, but leaded solder is easier to work with)
• Flux pen
• Tweezers
• Needle nose pliers (to bend leads and hold parts)
• Side cutters (to trim leads)

Other tools that are helpful:

• Blue mounting putty (to hold components in place while soldering)

Assembly

Here is the Pico v0.4 PCB:

Here is the schematic:

https://github.com/alanbjohnston/CubeSatSim/blob/pico/hardware/pico/v0.4/cubesatsim-pico-0.4_schematic.pdf

Before soldering the through-hole parts, the SMD parts such as the SAW filter, SR_FRS transmitter, USB-C, and clockgen components need to be mounted.

The instructions for this are here: Pico v0.2 SMD Instructions

The v0.4 board with all the SMD parts installed looks like this:

Through Hole Parts

First, solder the three integrated circuits (IC) U2, U4, and U8:

You will need to bend the pins slightly to insert them in the PCB. Pay attention to the "dot" on the IC that marks pin 1, and make sure it is in the upper left when the board is in this position.

Solder only one pin on each IC, then double check the pin 1 mark and the IC is inserted correctly before soldering the rest of the pins.

Next, mount the 1x20 female sockets for the Pico U1. NOTE: You can also solder the Pico directly onto the board if you are comfortable drag soldering SMD parts.

You can use the male pin headers to space and align the sockets for the Pico.

Or, if you have a Pico with the male headers already soldered in (Pico H), you can plug in the Pico to set the socket spacing and alignment while you solder the first pins. Solder one pin on each side of the socket, then check alignment before soldering the remaining pins.

When finished, it will look like:

For the antenna, either mount the

• SMA connector, X11 (not shown)
• The chip antenna, E1, and a 0 Ohm jumper R28:

• Or cut a length of tape measure to be 1/4 wavelength of 434.9 MHz (shown here)

Secure the tape measure antenna using the screw and the nut. The screw will cut threads as you turn it with pressure. Do not over tighten or the threads can get stripped.

Next, install the stacking GPIO header J1:

It is inserted on the bottom as shown here:

Flip the PCB over and solder all 40 pins on the top, being careful not to let the solder climb up the pin.

Next, install the 68 Ohm 1/2 Watt resistors R26 and R31. These resistors are fatter and longer than the other resistors since they have to attenuate the transmitter power. Also install the 180 Ohm R29.

Solder one pin at a time on the bottom of the PCB and make sure they are inserted correctly. Then solder the other pin and trim the excess leads with side cutters:

Here's how they look when they are installedL

If the SMD resistors R2 and R10 are not installed, install the 1k resistors R1 and R9. If the SMD resistors R23 and R25 are not installed, install the 4.7k resistors R20 and R22.

The CubeSatSim can now be tested in the FSK and BPSK modes. The Raspberry Pi Pico needs to be programmed first following these instructions:

1. Download the latest .UF2 file here: https://github.com/alanbjohnston/CubeSatSim/releases
2. Install it by following these steps:

• Plug your Raspberry Pi Pico into your computer using the micro USB port while holding down the BOOTSEL button (white button on the Pico). It should mount as a drive RPI-RP2.
• Drag the .UF2 file that you downloaded in step 1 to the Pico flash drive RPI-RP2.
• You can monitor the serial output using Arduino or a terminal emulator such as PUTTY to see the log files or make configuration changes.

You should receive a radio signal on 434.9 MHz. It will take a few seconds to power up. The built-in LED on the Pico will blink (unless you are using a Pico W which has WiFi - no LED will blink on this board) after a few seconds then stay on and blink off every 4 seconds or so. If you have a Ground Station with FoxTelem running, you can decode the packets. You can change modes by typing on the serial port (FSK is f while BPSK is b) or by pressing and holding the BOOTSEL button on the Pico (FSK is two blinks while BPSK is 3 blinks).

Install the Red, Green, and Blue LEDs LED3, LED4, and LED5, and the associated resistors R32, R34, and R35:

Solder the switch S1 and the RBF switch X1:

Next if the USB-C connector J9 isn't already installed, install the Sparkfun USB-C breakout board, J8, using a 1x6 pin header.

It is installed on the bottom of the PCB, but it is installed UPSIDE DOWN.

Also, note that the solder mask covers the holes on the top of the PCB making the soldering a bit tricky. I'd recommend applying liquid solder and using a very small amount of solder to ensure that a good electrical contact is made. This image shows both the surface mount USB-C on the top, and the USB-C breakout board soldered onto the bottom:

Install the capacitors C2 and C4 and resistors R3 and R8. C4 is an electrolytic capacitor that looks like a small can. It needs to be installed with the correct polarity. The PCB has a label for the + side, which is the upper pin in this photo. The capacitor itself typically has a label for the - lead, the shorter lead in this photo:

Now you can test in the APRS, SSTV, and CW modes. On startup and when changing modes, the built-in LED on the Pico and the blue LED will blink when the CW ID is transmitted and you should hear it at 434.9 MHz FM.

If you apply power to the USB-C connector at the top of the board, the red LED should illuminate. However, the Pico will not power up until diode D3 is installed in a later step:

Next, install the STEM green and blue LEDs LED1 and LED2 and the associated resistors R13 and R14.

Install the two diodes D3 and D7, being careful about the polarity.

These closeups show the correct polarity:

Install the diode D9 and 10k resistor R11 and capacitor C5. Install the right angle female socket J4 on the BOTTOM of the PCB.

Note the correct polarity of the diode D9:

The BME280 and MPU6050 sensors are mounted on the board through female pin sockets:

Solder the female pin sockets on the PCB and solder the pin headers on the boards, with the longer pins facing out (down in this photo):

With D3 in place, the Pico board can be powered through the USB-C connector and the battery board charged; the red LED will illuminate. With D7 in place, the micro USB connector on the Pico can be used to charge the Battery board as well.

The ESP32-CAM camera can also be plugged into the socket on the bottom of the PCB