At Just $6, Raspberry Pi Pico W Brings Wi-Fi to IoT Designs
First, Raspberry Pi unveiled Raspberry Pi Pico—the company's first MCU-class product. Now, that same board is getting a wireless connectivity facelift.
Raspberry Pi’s first-ever silicon solution, the RP2040, was introduced in January 2021. Recently, the company released a new RP2040 board that includes Wi-Fi capability. Let’s see how this new board can help designers build neater products with faster time-to-market.
The Highlights of RP2040
Raspberry Pi's first silicon solution, the RP2040 microcontroller, includes two Arm Cortex M0+ cores running at 133 MHz and including 264 KB of on-chip RAM. The device also supports up to 16 MB of off-chip Flash memory via a dedicated QSPI bus.
Raspberry Pi Pico. Image used courtesy of Raspberry Pi
A key advantage of the RP2040 over similar products is its programmable I/O (PIO) peripherals that can be used to implement different digital communication protocols as well as less common protocols such as the WS2812 LED protocol. The company also released the Raspberry Pi Pico, a $4 microcontroller board built using the RP2040 MCU.
A Glaring Shortcoming—And Two Potential Solutions
Raspberry Pi Pico is a low-cost breakout board for the RP2040. It pairs the RP2040 with 2 MB of Flash memory and a power supply chip that supports input voltages from 1.8–5.5 V. A major shortcoming of this low-cost board, however, is that it doesn’t provide wireless connectivity.
While IoT applications use both wired and wireless connectivity technologies, wireless solutions are typically preferred because they simplify deployment and configuration. In order to add wireless connectivity to an IoT device, we can use either a wireless SoC or a wireless module.
Option One: Use Wireless SoCs
While a wireless SoC (such as the CC3100 Wi-Fi network processor from Texas Instruments) can be used to add wireless connectivity to an IoT device, SoC-based designs require time, money, and engineering expertise.
Block diagram of the CC3100. Image used courtesy of Texas Instruments
When building a custom RF board, many factors can affect the circuit performance, including the board layout and material, antenna type, antenna trace shape, trace length, component type, and the component supplier. Even the placement of the board's screws and batteries can cause unknown adverse effects. A matching network is also required to ensure that the signal is not attenuated as it travels between the antenna and the SoC.
These RF design intricacies are the reason why experienced RF engineers are expensive. Additionally, RF design requires expensive lab equipment and tools. Considering all these hurdles, a custom RF implementation doesn’t seem like a reasonable solution for adding wireless connectivity to a low-cost board like the Raspberry Pi Pico.
Option Two: Use Wireless Modules
An alternative solution is to use a wireless module. Different chip manufacturers, such as Espressif Systems and Silicon Labs, have released numerous options for such modules. With a wireless module, a majority of the design is already done.
The PCB is fully characterized and optimized for RF performance. Antenna layout, shielding, timing components (crystals) as well as the regulatory approvals and standards certifications are all completed by the module manufacturer. This significantly simplifies the design process of a project.
Raspberry Pi Pico W Builds in Wireless Connectivity
Although wireless modules make wireless connectivity accessible to engineers and makers, they still require an additional board. To work around this problem, Raspberry Pi recently introduced a new version of the Pico board that includes Infineon’s CYW43439 wireless SoC (datasheet).
Raspberry Pi Pico W. Image used courtesy of Raspberry Pi
The new board, the Raspberry Pi Pico W, is priced at $6. The radio circuitry is encapsulated in a metal shield to reduce compliance costs for the customers’ end products. The CYW43439 includes IEEE 802.11 b/g/n MAC, baseband, and radio circuitry. The wireless SoC also integrates a power amplifier (PA) that meets the output power requirements of most handheld systems as well as a low-noise amplifier (LNA) for improved receiver sensitivity.
In addition to the mentioned Wi-Fi standards, the CYW43439 also supports Bluetooth Classic and Bluetooth Low Energy. While Bluetooth connectivity is not currently activated on the Pico W board, Raspberry Pi may include this functionality in future versions.
Other RP2040 Boards Also Eye Connectivity
Since the RP2040's release in January 2021, numerous third-party RP2040 boards have been produced by different vendors. Each one of these third-party boards attempts to provide an improvement on the original Raspberry Pi Pico board, which is the least expensive option. Of these boards, there are also solutions that come with built-in wireless connectivity. One example is Arduino’s Nano RP2040 Connect. The functional block diagram of this board is shown below.
Block diagram of the Nano RP2040 Connect. Image used courtesy of Arduino
The Nano RP2040 Connect uses the u-blox Nina W102 module to provide Wi-Fi and Bluetooth connectivity. u-blox's wireless module supports IEEE 802.11 b/g/n and Bluetooth 4.2 standards. The module also includes an integrated planar inverted-F antenna (PIFA).
The Nano RP2040 Connect features some additional components such as a 6-axis IMU and an omnidirectional digital microphone. The board is priced at about $30, which is much more expensive than the Pico W board.
A Final Thought: The Pros and Cons of Wi-Fi
There are several different wireless protocols, such as Wi-Fi, Bluetooth LE, Zigbee, and Z-Wave, that are commonly used in IoT applications. When assessing wireless solutions for IoT applications, “one size doesn’t fit all.” But what are the pros and cons of Wi-Fi—particularly for the Pico W board and some other RP2040 projects on the internet?
Wi-Fi has one outstanding feature: it is natively IP-based. This is because, from day one, Wi-Fi was created for internet connectivity as a wireless replacement for the wired Ethernet standard. With this in mind, Wi-Fi is the best choice when we want an IoT device to natively connect to the internet.
Devices that use protocols such as Bluetooth and Zigbee cannot directly connect to the internet for cloud or remote access. In these cases, a hub or gateway device is required to convert the information from a Bluetooth/Zigbee/Z-Wave format to Wi-Fi before sending the data over the internet through a Wi-Fi router. This extra gateway adds to the system cost and complexity.
However, when applied to IoT applications, traditional Wi-Fi has two main limitations: it cannot efficiently support a large number of devices at the same time and it has a high power consumption. A recent upgrade to Wi-Fi, referred to as Wi-Fi 6 or 802.11ax, is designed with an eye on facilitating IoT applications. Wi-Fi 6 supports crowded IoT networks while burning much less power.
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