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Raspberry Pi Pico W BackPack Our Raspberry Pi Pico BackPack from March 2022 has a powerful dualcore 32-bit processor, 480 × 320 pixel colour touchscreen, onboard real-time clock, SD card socket, stereo audio output and infrared receiver. Now, for only about $5 more, it has WiFi too! Project by Tim Blythman M icrocontrollers have become so easy to use, cheap and accessible for hobbyists, while chips like the ESP8266 have made it simple to use WiFi. The Raspberry Pi Foundation’s Pico W is an inexpensive, well-documented 32-bit microcontroller board with WiFi that is well-suited to being used with the LCD BackPack. We reviewed the Pico W in the November 2022 issue and found that it was mostly interchangeable with the Pico (siliconchip.au/Article/15547) but with added WiFi support. So it was only natural for us to update the Pico BackPack to include WiFi support using the Pico W. As it turns out, that was not hard to do. From launch, the Pico supported the MicroPython and C languages (using the Raspberry Pi Foundation’s Features and Specifications ∎ Includes a 3.5in LCD touch panel and a dual-core microcontroller with WiFi. ∎ Also includes all the features of the original Pico BackPack. ∎ We provide software demos and examples for the Arduino IDE, C SDK and MicroPython. ∎ Our sample code demonstrates practical uses of HTTP, UDP and NTP. 50 Silicon Chip Raspberry Pi is a trademark of the Raspberry Pi Foundation C software development kit). Arduino support in the form of the Arduino Pico board profile came soon after. The Raspberry Pi Foundation has made many inexpensive single-board computers and microcontroller boards available to the masses, even amid continuing electronics component shortages. The Pi Pico series are simple but well-thought-out boards and are attractively priced for what they offer. BackPack hardware We considered whether it was worthwhile to update the Pico BackPack PCB to complement the Pico W, but ultimately, we decided not to make any significant changes. The thing is that the Pico BackPack crams a lot of features into a small area corresponding to the size of the matching LCD touch panel. To add any features would likely mean removing some of the existing features, which we didn’t want to do. The Pico BackPack has a row of I/O pins to make external connections, so it’s easy enough to connect different hardware if necessary. Thankfully, we’d already established that the Pico W didn’t ‘break’ any existing functionality of the Pico BackPack. So the BackPack PCB remains the same for the Pico W, although we will recommend a minor Australia's electronics magazine assembly variation to enhance the WiFi capability. The Pico W BackPack The only substantial difference between the Pico BackPack and the Pico W BackPack is the replacement of the Pico module with a Pico W. All the pins on the Pico W are labelled the same as those on the Pico, so none of the signals or I/O pin breakouts need to change. Still, as we noted in our review of the Pico W, both the BackPack PCB and LCD touch panel have large solid copper areas that could impede WiFi signal propagation. Therefore, we recommend that the Pico W is mounted slightly away from the BackPack PCB to provide better clearance for its onboard WiFi antenna. We used header strips to provide this spacing. You could also use low-profile socket headers and short pin headers if you wish to make the Pico W pluggable. We tried this and found it worked well, although it was fiddly to assemble. Circuit details Fig.1 shows the circuit diagram for the Pico W BackPack. It is identical to the original Pico BackPack, with the Pico replaced by a Pico W. IRRX1 at top left allows the Pico W to receive IR signals on its GP22 digital siliconchip.com.au Fig.1: the Pico W BackPack circuit is almost identical to the Pico BackPack. It includes an IR receiver, microSD card, real-time clock, audio output and LCD touch panel. A 20-way header provides access to power and spare I/O pins for adding more features. The 1kW resistor at IRRX1’s output is not needed in most cases. input. The LCD touch panel connects to power and the SPI bus at the top, as does the microSD card socket at upper right. The two transistors on the right control the power to the LED backlight on the LCD touch panel. Below this, a DS3231 real-time clock and calendar IC connects to the I2C bus. siliconchip.com.au Finally, the components at the bottom, including the op amps, can deliver line-level audio at CON3. They connect to pins on the Pico W that generate pulse-width modulated (PWM) signals to provide synthesised analog voltages. For more details and specifics about how the various features work on the Australia's electronics magazine Pico BackPack PCB, refer to the article from March 2022 (siliconchip.au/ Article/15236). The original software to interface to the BackPack hardware was also explained in that article. Construction While that March 2022 article has more detail on assembling the PCB January 2023  51 removable. We figure it’s inexpensive enough that you are better off saving the effort and just soldering it. Software with WiFi support The release of the Pico W has allowed us to update the Pico BackPack with WiFi. It’s a powerful combination that we think will be the basis of some diverse and interesting projects. We’re providing several practical WiFi demos to make it easy to pick up and use. and fitting it to the LCD touch panel, experienced constructors should have no trouble using the overlay in Fig.2 to assemble the PCB. If you refer to that earlier article, the PCB construction is no different until you get to the Pico W module. Most IR receivers will not need the 1kW resistor; in fact, it will interfere with their weak internal pullup. Hence, it has been omitted from the overlay and is not seen in our photos. Don’t forget the cell holder on the reverse of the PCB if you are fitting the real-time clock IC. Lines separate the various sections of the board on the silkscreen. That helps you to omit some components if you wish to reclaim some I/O pins by not using those features. As we mentioned earlier, the Pico W should be spaced away from the main BackPack PCB and also kept clear of the LCD above. Thus, we have added two 20-way pin header strips to the parts list. Solder these to the BackPack PCB, with the plastic carrier sitting above. Then solder the Pico W to the top of the pin headers. The plastic carrier separates the Pico W from the BackPack PCB. Our photos show how the Pico W is spaced above the BackPack PCB by a small distance. The other option requires low-­ profile (5mm) header sockets too. Altronics Cat P5398 can be used but you will need two lengths, cutting them down to 20 pins each. 52 Silicon Chip The fiddly part is fitting the pin headers to the Pico W, as this requires removing the metal pins from their plastic carrier to minimise the height. Although the plastic carrier is only 2.5mm high, it’s enough to cause the Pico W to foul the LCD, so it must be removed. After pulling the pins out of the plastic carrier, insert them individually into the socket header entries. You can then place Pico W over the pins and solder them to it. Depending on the length of the pins, they might also need to be trimmed so that the pins do not foul the LCD screen. The only advantage of that more fiddly approach is that the Pico W is Of course, we need some sample code that uses WiFi to show off the Pico W’s new feature. Since PicoMite BASIC will not support the Pico W’s WiFi (as noted in the November review article), our software samples do not include PicoMite BASIC. Existing PicoMite BASIC programs should work fine on the Pico W, with the minor exception that the Pico W’s onboard LED is driven differently, so it can’t be controlled as it would be on a Pico. We have updated the Arduino, C SDK and MicroPython examples to add WiFi features. As we noted in our review of the Pico W, a document called “Connecting to the Internet with Raspberry Pi Pico W” explains how to do this with the C SDK and MicroPython. But that guide is quite basic; our sample code does much more. Since the updated demos are based on the earlier versions we made for the original Pico BackPack, we recommend reading the original Pico BackPack article for information on the original features. One of the great features of the Pico and the Pico W is the bootloader which implements a virtual flash drive, allowing software to be uploaded by simply copying a file to the virtual drive. The bootloader is in mask ROM in the RP2040 microcontroller that runs the Pico and Pico W. This makes it Fig.2: the lines on the overlay delineate the components that provide the different features of the Pico W BackPack. There is also a cell holder on the rear of the PCB, used by the real-time clock IC to keep time when power is not otherwise available. The Pico W is spaced above the main PCB to improve the performance of its WiFi antenna. Australia's electronics magazine siliconchip.com.au practically impossible to ‘brick’ the Pico or Pico W as the bootloader cannot be overwritten. Bootloader mode is entered by holding down the BOOTSEL button on the Pico or Pico W while powering up or resetting the chip. Since the BackPack provides a reset button, you can start the bootloader by pressing and holding BOOTSEL while pressing S1 on the BackPack. Software images for the Pico and Pico W use the UF2 file type, which is a binary format, unlike the text-based HEX files used for other chips like PIC microcontrollers. If you are simply interested in seeing what the Pico W BackPack is capable of doing, all you need to do is copy the respective UF2 file to it after putting the Pico W into bootloader mode. We’ll go into a bit more detail about the workings of the software later in this article. To simplify entering the WiFi credentials, you can set them using the virtual serial port. You will need a serial terminal program, such as Tera­ Term, minicom or the Arduino Serial Monitor, to communicate with the Pico W. You might notice that the demo .uf2 files are larger than the Pico examples due to the extra libraries needed to communicate with the WiFi chip. The WiFi chip also needs a 300kB binary ‘blob’ to work, which is bundled into the firmware images. Arduino coding The team that created the Arduino-­ Pico port for the Arduino IDE has done a good job of aligning the Pico W’s WiFi API (application programming interface) to that used by other WiFi boards, such as those based on the ESP8266 and ESP32 processors. Indeed, it is based heavily on that of the ESP8266. You might remember the D1 Mini BackPack from the October 2020 issue (siliconchip.au/Article/14599). It uses an ESP8266-based D1 Mini module to drive an LCD touch panel and has many features in common with the Pico W BackPack. We’re using version 2.5.2 of the Arduino-Pico board profile, although versions as old as 2.30 should support the Pico W. You can find more information about the board profile at https://github.com/earlephilhower/ arduino-pico siliconchip.com.au Parts List – Pico W BackPack 1 double-sided PCB coded 07101221, 99 x 55mm 1 Raspberry Pi Pico W Module (MOD1) [Altronics, Core, Digi-Key, Little Bird] 1 3.5in LCD touchscreen [Silicon Chip Shop Cat SC5062] 1 14-pin, 2.54mm pitch socket header (for LCD panel) 3 20-pin, 2.54mm pitch pin header (CON2 & to mount Pico W) 2 20-pin low-profile (5mm tall) 2.54mm pitch socket headers (optional) 2 2-pin, 2.54mm pitch pin headers with jumper shunts (JP1, JP2) 1 6mm x 6mm tactile switch (S1) 8 M3 x 6mm panhead machine screws 4 M3 x 12mm tapped spacers Semiconductors 1 IRLML2244TRPBF/SSM3J372R P-channel Mosfet, SOT-23 (Q1) 1 2N7002 N-channel Mosfet, SOT-23 (Q2) Resistors (all M3216/1206, 1%, ⅛W) 1 10kW 1 1kW Optional Components SD card 1 SMD microSD card socket (CON1) [Altronics P5717] 1 10μF 10V X7R SMD ceramic capacitor, M3216/1206 size 1 100nF 10V X7R SMD ceramic capacitor, M3216/1206 size Real time clock/calendar 1 surface-mounting CR2032 cell holder (BAT1) [BAT-HLD-001] 1 DS3231 or DS3231M in SOIC-16 (wide) or SOIC-8 package (IC1) 1 100nF 10V X7R SMD ceramic capacitor, M3216/1206 size 2 4.7kW 1% ⅛W M3216/1206 size IR receiver 1 3-pin infrared receiver (IRRX1) [Jaycar ZD1952] 1 10μF 10V X5R SMD ceramic capacitor, M3216/1206 size 1 1kW 1% ⅛W resistor M3216/1206 size (see text) 1 470W 1% ⅛W resistor M3216/1206 size 1 100W 1% ⅛W resistor M3216/1206 size Stereo audio 1 MCP6272(T)-E/SN, MCP6002(T)-I/SN or -E/SN dual op amp, SOIC-8 (IC2) 1 3-pin, 2.54mm pitch pin header (CON3) 2 1nF 25V X7R SMD ceramic capacitors, M3216/1206 size 2 100nF 10V X7R SMD ceramic capacitors, M3216/1206 size 2 10uF 10V X5R SMD ceramic capacitors, M3216/1206 size 4 100kW 1% ⅛W resistor M3216/1206 size 2 47kW 1% ⅛W resistor M3216/1206 size 2 22kW 1% ⅛W resistor M3216/1206 size 2 10kW 1% ⅛W resistor M3216/1206 size 2 100W 1% ⅛W resistor M3216/1206 size As well as adding WiFi support, we’ve updated the Arduino sample code to include an infrared receiver decoding library. In our original Pico BackPack article, we mentioned that we expected the IRRemote library to be ported to the Pico (and Pico W), which has now happened. You can find that library online at https://github.com/Arduino-Irremote/ Arduino-Irremote or it can be installed by searching for “irremote” in the Arduino Library Manager. We have also included a copy of the version Australia's electronics magazine we’ve used in the software bundle. Screen 1 shows the BackPack running our updated Arduino Pico W sample. We have added some text to the LCD panel to show the status of the WiFi hardware. Setting up the WiFi Since using the Pico W in a meaningful way requires that it connect to a WiFi network, we have added a configuration menu on the virtual serial port. We did it that way, rather than using the touchscreen, because it’s easier to January 2023  53 ► Screen 1: the Arduino demo for the Pico W has the most features, primarily due to the excellent library support the Arduino community offers. Apart from the new WiFi features, there is now also support for the IR receiver. ► Screen 2 (right): all the demos include a menu system that can be accessed from a serial terminal program. This is to simplify entering the WiFi credentials needed for the demo to work. The Arduino output is shown here. enter WiFi credentials via a computer rather than an on-screen keyboard. Screen 2 shows the menu that is presented over the serial port by the Arduino software. Items are selected by typing the number and pressing the Enter key. Items 2 and 3 will prompt for the SSID name and password, also followed by Enter. This demo can scan for WiFi networks and connect by name and password. It can also connect to a website over HTTP to retrieve data from the internet. In this case, we use ip-api. com to get some location text to display, along with a timezone offset for that location. This isn’t perfect and would probably be fooled by a VPN (virtual private network), but it will usually give the correct timezone. We think it is a simple and effective way of demonstrating the use of HTTP on the Pico W. We also use NTP (network time protocol) to provide the current time in UTC, adjusted by the timezone offset to provide accurate local time. This can then be saved to the RTC IC on the BackPack. To do all this, you would use menu items 2, 3 and 4 to connect to a WiFi network, followed by 8 to get the offset and 7 to set the RTC. You can set the offset manually using item 6 if item 8 does not work. The IRRemote library is also used to capture and decode IR signals, as displayed in the line beginning “NEC” in Screen 1. This indicates that an NEC 54 Silicon Chip code was last received and shows that code. Code differences The Arduino code for the updated Pico W Backpack differs from the earlier Pico BackPack example only in the main sketch file, plus the requirement to have the IRRemote library installed. It uses other library files that are part of the Arduino-Pico board profile, including those needed for WiFi. Those who have worked with modules based on the ESP8266 or ESP32 will be familiar with how WiFi works under the Arduino IDE; the Pico W is similar. Three library includes are used to implement the WiFi features: #include <WiFi.h> #include <WiFiUdp.h> #include <HTTPClient.h> NTP requires the UDP protocol for communication, hence its inclusion. Fetching web pages uses HTTP. Scanning for networks is done by running a single line of code, as is connecting to a network: WiFi.scanNetworks(); WiFi.begin(ssidname,ssidpass); These calls are blocking (ie, the program doesn’t proceed until the action is completed), and the latter can take up to ten seconds to run. So they may not suit all applications. The C SDK gives better access to the low-level commands and might be more suited if blocking calls are not desired. Australia's electronics magazine It is possible to use function calls from the C SDK in the Arduino IDE, but we preferred to keep the Arduino code consistent with the Arduino way of doing things. NTP is implemented as a background routine that simply needs to be started and then quietly synchronises in the background. Fetching a website using HTTP can be done in a few lines: http.begin(wificlient,URL); httpCode=http.GET(); Serial.print(“Return code:”); Serial.println(httpCode); if(httpCode == 200) { Serial.println( http.getString() ); } We got around some of the longer blocking sections by using the second processor core to do some tasks in the background without interrupting the main program flow. These can be seen in the setup1() and loop1() functions. At the time of writing, we have not seen an official Arduino board profile for the Pico W, so we were unable to try this out as we did for the Pico. But the Arduino-Pico board profile appears to be updated regularly and works well; we have no hesitation in recommending it. Using it with the C SDK Screen 3 shows the LCD panel of the BackPack loaded with the C SDK (software development kit) demo. It siliconchip.com.au as it gets updated in time. This means that the main program is not blocked from other operations while network activity occurs. Using HTTP requires several callback functions to be set, meaning that using the C SDK can seem a bit more complicated than using the Arduino IDE. Still, if you have the patience to set up and delve into the C SDK, we recommend trying it, especially if you need to get the most performance from your Pico W BackPack. MicroPython Screen 3: the C SDK demo runs fast, with good access to low-level functions. Support for protocols like NTP and HTTP is very good once you get it working. includes similar elements to the Arduino example, although the C SDK does not have library support for the IR receiver or RTC chip. There is an RTC feature in the Pico W (and Pico) that can be used by C SDK, but it doesn’t provide the battery backup timekeeping feature that chips like the DS3231 have. It needs the time to be set each time Pico W is reset. Since the Pico W uses a crystal oscillator, it should be pretty accurate once it has been set. The C SDK performs similar tasks to the Arduino demo, using a WiFi connection and NTP to update the RTC. Location and timezone data are also fetched from ip-api.com using HTTP. Several library files are needed for WiFi support. The first file is required to interface with the Infineon CYW43439 chip that provides the WiFi interface, while the others provide library support for HTTP and NTP: Pi computer, we ran it on a Windows PC using the pico-setup tool that can be found at https://github.com/ndabas/ pico-setup-windows This resulted in many minor glitches, especially as some of the commands are subtly different. If you have a Raspberry Pi computer handy, you might find it more straightforward to program the Pico W via the C SDK. Just as for the original Pico BackPack demos, the C SDK software runs very fast and some lower-level functions allow more control than we could easily achieve with the Arduino IDE. In most cases, the serial port menu is used to start an action, such as starting a network scan or connecting to a WiFi network. These do not return immediately like the Arduino equivalents. Instead, the main program monitors the status of variables like the Pico W’s IP address and displays information The MicroPython version available for the Pico W at the time of writing is tagged as ‘unstable’, although we did not have any issues using it. We have included a copy of this version with our software bundle. Note that there are different MicroPython UF2 files for the Pico and Pico W. Be sure to use the correct version. Our MicroPython demo has much the same features as the C SDK demo, as shown in Screen 4. We haven’t made any changes to the two library files (from the original Pico BackPack demo); only the “main.py” file has been updated. Like the Arduino IDE, several libraries must be imported to provide WiFi functionality: import network import urequests import ntptime We noted that the original Micro­ Python software was barely fast enough to be useful. The addition of the WiFi features does make interacting with the LCD touch panel quite slow. Still, we expect most people would not try to cram in all the features that we have. Like the Arduino code, many #include “pico/cyw43_arch.h” #include “lwip/apps/http_client.h” #include “lwip/apps/sntp.h” To properly use the C SDK with the Pico W, we had to make a few changes to the CmakeLists.txt file, especially in the target_link_libraries and add_definitions sections. Look at our sample project to see what to do before creating your own projects. While the C SDK is primarily intended to be used on a Raspberry siliconchip.com.au This shows the spacing needed to give clearance for the Pico W’s WiFi antenna. Short pin headers are the simplest way to achieve this while also keeping clear of the LCD touch panel, which is mounted above. Australia's electronics magazine January 2023  55 it uses a compiled rather than interpreted language. The C SDK was a bit more tricky to work with, but the results are fast and responsive. It also gave us much better access to low-level operations. Bluetooth will be a nice feature to have when it arrives, but as it stands, the Pico W is very useful at its current price and works very well with the BackPack hardware. Now that we have WiFi working well with the C SDK, we think the Pico W will be a good choice for future projects needing WiFi. The Arduino IDE will be a handy option when we want to quickly interface with hardware, especially if it needs library support. Availability Screen 4: the MicroPython demo has similar capabilities to that of the C SDK. It’s possible to use the drawing feature of the demo, but it is not very responsive. MicroPython routines are blocking and may not return for many seconds. The features available are much the same as the C SDK, with options to scan for networks and set the SSID name and password. You can connect, disconnect and make an HTTP request to retrieve data. Is there Bluetooth support? Since the Infineon CYW43439 WiFi chip has support for Bluetooth, many people have been left wondering whether the Pico W will be able to use Bluetooth. At the time of writing, it appears that is not the case. Instead, we are simply left with the tantalising statement from the folks at the Raspberry Pi Foundation that it “may be enabled in the future”. Summary Our demo code does many things you might typically do with a WiFi-­ capable microcontroller: connect to a network, make HTTP requests to fetch data from websites and use NTP to set the time. The Arduino IDE (using Arduino-­ Pico) and MicroPython made this very easy. We found the Arduino IDE more attractive as it has better library support, and the code runs quicker since At the time of writing, the Pico W was available from: ∎ Altronics (Z6424) siliconchip.au/link/abi5 ∎ Digi-Key Electronics (SC0918) siliconchip.au/link/abgw ∎ Core Electronics (CSE08703) siliconchip.au/link/abgx ∎ Little Bird Electronics (SC0918) siliconchip.au/link/abhj Other retailers we expect might stock the Pico W when it becomes available in volume include element14 SC and Mouser. SC6625 Kit ($85 + P&P) includes all parts in the parts list except the socket headers and DS3231 IC (the DS3231 is available separately – SC5103 or SC5779). U Cable Tester S B Test just about any USB cable! USB-A (2.0/3.2) USB-B (2.0/3.2) USB-C Mini-B Micro-B (2.0/3.2) Reports faults with individual cable ends, short circuits, open circuits, voltage drops and cable resistance etc November & December 2021 issue siliconchip.com.au/Series/374 DIY kit for $110 SC5966 – siliconchip.com.au/Shop/20/5966 Everything included except the case and batteries. Postage is $10 within Australia, see our website for overseas & express post rates 56 Silicon Chip Australia's electronics magazine siliconchip.com.au