This is a simple web page to demonstrate the use of Raspberry Pi Pico W with Waveshare Pico-ePaper 3.7" E-ink Display to display the when the next train to the office is.
Raspberry Pi Pico W
Raspberry Pi Pico is a low-cost, high-performance microcontroller board with flexible digital interfaces.
Key features include:
- RP2040 microcontroller chip designed by Raspberry Pi in the United Kingdom
- Dual-core Arm Cortex M0+ processor, flexible clock running up to 133 MHz
- 264KB of SRAM, and 2MB of on-board flash memory
- USB 1.1 with device and host support
- Low-power sleep and dormant modes
- Drag-and-drop programming using mass storage over USB
- 26 × multi-function GPIO pins
- 2 × SPI, 2 × I2C, 2 × UART, 3 × 12-bit ADC, 16 × controllable PWM channels
- Accurate clock and timer on-chip
- Temperature sensor
- Accelerated floating-point libraries on-chip
- 8 × Programmable I/O (PIO) state machines for custom peripheral support
Raspberry Pi Pico W adds on-board single-band 2.4GHz wireless interfaces (802.11n) using the Infineon CYW43439 while retaining the Pico form factor. The on-board 2.4GHz wireless interface has the following features:
- Wireless (802.11n), single-band (2.4 GHz)
- WPA3
- Soft access point supporting up to four clients
-
Bluetooth 5.2
- Support for Bluetooth LE Central and Peripheral roles
- Support for Bluetooth Classic
Waveshare Pico-ePaper 3.7" E-ink Display
| Pin Name | Pin Description |
|---|---|
| VCC | 3.3V/5V |
| GND | Ground |
| DIN | SPI MOSI/POCI pin |
| CLK | SPI SCK pin |
| SS/CS | SPI chip selection, low active |
| DC | Data / Command selection (high for data, low for command) |
| RST | External reset, low active |
| BUSY | Busy status output |
Key features include:
- 3.7" E-ink display with 480x280 resolution
- >170° Viewing angle
- Black and white colour
- Four greyscale levels
- No backlight, keeps displaying last content for a long time even when power down
- Ultra low power consumption, basically power is only required for refreshing
- SPI interface, requires minimal IO pins
- Onboard voltage translator, compatible with 3.3V / 5V MCUs
- Comes with development resources and manual (Raspberry Pi Pico C/C++ and MicroPython examples)
Wiring Schedule
| Raspberry Pi Pico W | Waveshare Pico-ePaper 3.7" E-ink Display |
|---|---|
| VCC | VSYS |
| GND | GND |
| DIN | GP11 |
| CLK | GP10 |
| CS | GP09 |
| DC | GP08 |
| RST | GP12 |
| BUSY | GP13 |
SPI Communication
Sending and Receiving Data
SPI (Serial Peripheral Interface) is a synchronous serial communication protocol used for short-distance communication, primarily in embedded systems. It allows a controller device to communicate with one or more peripheral devices using a full-duplex communication method. SPI is widely used for connecting microcontrollers to various peripherals such as sensors, displays, and memory devices.
It's a "synchronous" data bus, which means that it uses separate lines for data and a "clock" that keeps both sides in perfect sync. The clock is an oscillating signal that tells the receiver exactly when to sample the bits on the data line. This could be the rising (low to high) or falling (high to low) edge of the clock signal. When the receiver detects that edge, it will immediately look at the data line to read the next bit. Because the clock is sent along with the data, specifying the speed isn't important, although devices will have a top speed at which they can operate.
Chip Select and Multiple Peripherals
SPI Bus? SPI device? What's the difference?
The SPI bus is the communication pathway - or channel that allows data to be transferred between devices. Hense, many SPI devices (peripherals) can use the SPI bus to communicate with the Rapsberry Pi Pico (controller). The Infineon CYW43439 (802.11n wireless) chip also uses SPI for communication. Thankfully, the Raspberry Pi Pico W has two SPI busses available, so in this case both the display and the wireless peripherals can communicate at the same time.
How does the bus know where to send the data if I have multiple devices?
There are a couple of ways that electronics handle serial communication. The SPI bus requires a chip select pin to be connected between the controller and peripheral, with it being held low for the duration of the communication. Multiple peripherals can share the same but, so long as there are enough output pins on the controller to allow for selection.
Flashing to the Raspberry Pi Pico W
todo!