Chapter 11: Let's Build a Product!

In this chapter, we will discuss building a product using the Raspberry Pi Pico. We will design a carrier Printed Circuit Board (PCB) for the Pico where we will interface a cellular module to send messages to the cloud. We will also discuss how to build a Pico phone, as shown in the following figure. In this chapter, we will specifically discuss the product development process that's involved in designing a PCB.

Figure 11.1 – Pico phone

In this chapter, we will cover the following topics:

• Understanding the Pico phone
• Capturing the requirements
• Designing a PCB
• Bringing up the board
• Taking the project forward

Technical requirements

The software and hardware files for this chapter can be found at https://bit.ly/35088w4.

The following hardware is required for this chapter:

• Raspberry Pi Pico (https://bit.ly/3AJtoAf): USD 4.
• Blues Wireless Notecard (https://bit.ly/3wnFbWc): USD 65.
• Cellular Antenna (https://bit.ly/3N91Sn1): USD 11.50.
• Qwiic Keypad (https://bit.ly/3JwIJJd): USD 11.50.
• Fabricated PCB: The prices vary based on the manufacturer.
• PCB components: The prices depend on the components. The Bill of Materials (BoM) is available in this book's GitHub repository (shared previously).
• Soldering supplies, including a reflow oven.

Code in Action videos for this chapter can be viewed at https://bit.ly/38Th2gy.

Installing CircuitPython

We are assuming that you have installed CircuitPython on your Pico. If you are not familiar with the installation process, we recommend following the installation process provided in Chapter 1, Getting Started...

Understanding the Pico phone

We built the Pico phone in 2021 and published it as a Hackster project (https://bit.ly/3pY7J5e). The project originated when we wanted to evaluate a cellular module. We chose this project to describe the product development process because it was one of 21 featured projects of 2021 (https://bit.ly/3CXh3ec) and it was also featured in the March 2022 edition of the Hackspace magazine (https://bit.ly/3CYAJ1l), which was published by the Raspberry Pi foundation. The magazine is free to download.

Hackster Article versus This Chapter

While the Hackster project discusses texting a joke to a phone number, we will discuss the product development aspects of the project. Specifically, we will discuss capturing the requirements, building the prototype, and more.

In the next section, we are going to discuss capturing the requirements for the product.

Capturing the requirements

In this section, we will discuss capturing the requirements for our product. Before we start developing a product, we need to capture the requirements for our product. We also need to understand whether it is feasible to make a product.

To determine this feasibility, we need to understand our product's purpose. Let's define some requirements for our product:

• The product needs to have some form of network connectivity to connect and upload data to the cloud.
• The product needs to have a keypad to capture user inputs.
• The product needs to use a Raspberry Pi Pico. This will allow you to use the RP2040 microcontroller in future revisions. The first version would make use of the Pico, while future revisions would use the RP2040 microcontroller integrated directly onto the PCB.
• The device can be powered using a USB cable (by using the Pico's USB connector) or using a DC power jack.

In the real world, the product would...

Designing a PCB

In this section, we will discuss designing a PCB. A PCB refers to a board where the connections between the components are routed using copper. These connections are called traces and the following figure shows the traces on a typical PCB:

Figure 11.9 – Traces on a typical PCB

We recommend the learning guide on PCBs from SparkFun: https://learn.sparkfun.com/tutorials/pcb-basics/all.

In case you are not familiar with designing PCBs, we recommend the following course https://teachmepcb.com/.

PCB Design Software

There are various design tools available for designing PCBs. For this chapter's project, we used Autodesk Eagle. However, other tools are available, including KiCad, Altium, and others. KiCad is an open source project that is free to use. We used Eagle but there are plenty of learning resources available for KiCad.

Any PCB design has six major components to it, as follows:

• Schematic capture
• PCB layout...

Bringing up the board

In this section, we will discuss board bring-up. Board bring-up is a process where we verify the functionality of our design in a step-by-step process. It is identical to the steps we discussed earlier to test the Notecard and the SparkFun Qwiic keypad. During the verification process, we found a missing connection in our schematic. We connected it using a piece of wire (as shown in the following figure) and verified its functionality:

Figure 11.16 – Fixing a missing connection using a piece of wire

Now that we have tested our PCB, it is time to revise our design by adding the missing connection to the schematic.

Final assembly and testing

It is time to build our final product. We ordered an old landline phone with a keypad and gutted its internal circuitry. We glued our keypad and placed our PCB inside the phone. Our Pico phone looks like this:

Figure 11.17 – Assembled Pico phone

We recommend...

Taking the project forward

So far, we have used the Pico as-is to develop our product. It is not practical to use the Pico development board for all designs. Some possible reasons are as follows:

• The size of the Pico board might not be suitable for your product.
• You might not need all the pins that are available on the Pico microcontroller.
• Compared to the Pico, an RP2040 microcontroller costs USD 1, but you do have additional components.

In the next section, we will discuss some options to replace the Raspberry Pi Pico in our design.

Replacing the Pico

To replace the Pico with a custom design based on the RP2040 microcontroller, we need to follow a reference design or an application note. Fortunately, the Raspberry Pi Foundation provides a document called Hardware design with RP2040 (available at https://datasheets.raspberrypi.com/rp2040/hardware-design-with-rp2040.pdf). The document details all the components that are needed for your design.

We will...

Summary

In this chapter, we discussed building a product using the Raspberry Pi Pico. We discussed building a proof-of-concept and verifying the individual components. Then, we performed schematic capture and PCB layout using Autodesk Eagle. This was followed by fabrication, assembly, and board bring-up.

We hope you enjoyed going behind the scenes and understanding the various steps involved in building a product. In the next chapter, we will discuss various tips and tricks you should keep in mind before we wrap up this book.