Raspberry Pi Compute Module 4S: The Tiny Powerhouse for Embedded Projects
A compact, powerful module based on the Raspberry Pi 4, designed for integration into custom hardware and demanding embedded applications.
The Raspberry Pi Compute Module 4S is a highly integrated System-on-Module (SoM) designed for industrial and commercial applications where a small form factor and high performance are critical. It takes the core processing capabilities of the popular Raspberry Pi 4 Model B and packages them into a compact board-to-board connector form factor, making it ideal for custom carrier boards and high-volume production runs. This board is not intended for direct use like a typical Raspberry Pi but requires a custom carrier board to expose its interfaces.
At its heart, the CM4S features the Broadcom BCM2711, a quad-core ARM Cortex-A72 processor, clocked at 1.5GHz. This SoC provides significant computational power, suitable for running complex operating systems, machine learning inference, and multimedia processing. It supports a wide range of peripherals, which are brought out via the high-density connectors on the module, offering flexibility for designers to tailor their hardware to specific needs.
Positioned as a successor to previous Compute Modules, the CM4S offers enhanced performance and connectivity options compared to its predecessors. It retains the flexibility of the CM series, allowing developers to integrate Raspberry Pi computing power into their own product designs without the constraints of the standard Raspberry Pi board's fixed interfaces. This makes it a compelling choice for makers, students, and embedded engineers looking to build custom IoT devices, industrial controllers, digital signage, or other embedded systems that demand more than a microcontroller can offer.
The CM4S is particularly suited for projects requiring a full Linux environment, significant processing power, and extensive I/O capabilities in a small footprint. Its design encourages custom hardware development, making it perfect for those who need to integrate computing into unique enclosures or create specialized interfaces not found on standard development boards. It's a step up from typical microcontrollers, offering a familiar Raspberry Pi experience in a more embedded-friendly package.
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Specifications
| Microcontroller / SoC | Broadcom BCM2711 |
| Architecture | 64-bit Quad-core ARM Cortex-A72 |
| Clock speed | 1.5GHz |
| Flash / Storage | No onboard eMMC/SD card; requires external storage via carrier board (e.g., SD card, eMMC, NVMe) |
| RAM / SRAM | Available in 1GB, 2GB, 4GB, or 8GB LPDDR4-3200 SDRAM options |
| Operating voltage | 3.3V (for module interfaces) |
| Digital I/O pins | Up to 28 GPIO pins exposed via 2x 100-pin connectors |
| Analog / ADC | No built-in ADC; requires external ADC for analog input |
| PWM | Up to 6 PWM channels available |
| Connectivity | Gigabit Ethernet PHY (requires external connector), Wi-Fi (optional 2.4GHz/5GHz 802.11ac), Bluetooth 5.0 (optional) |
| USB | 2x USB 3.0 ports, 2x USB 2.0 ports (via carrier board) |
| Power input | Typically 5V DC via carrier board; module itself requires stable power from carrier board regulators |
| Dimensions | 67.6mm x 30.5mm x 4.1mm |
Pinout & pin functions
| Pin | Function |
|---|---|
| 3V3 | Power output (3.3V) |
| GND | Ground |
| GPIO0 | General Purpose Input/Output |
| GPIO1 | General Purpose Input/Output |
| GPIO2 | General Purpose Input/Output |
| GPIO3 | General Purpose Input/Output |
| GPIO4 | General Purpose Input/Output |
| GPIO5 | General Purpose Input/Output |
| GPIO6 | General Purpose Input/Output |
| GPIO7 | General Purpose Input/Output |
| GPIO8 | General Purpose Input/Output |
| GPIO9 | General Purpose Input/Output |
| GPIO10 | General Purpose Input/Output |
| GPIO11 | General Purpose Input/Output |
| GPIO12 | General Purpose Input/Output |
| GPIO13 | General Purpose Input/Output |
| GPIO14 | General Purpose Input/Output (UART0_TX) |
| GPIO15 | General Purpose Input/Output (UART0_RX) |
| GPIO16 | General Purpose Input/Output |
| GPIO17 | General Purpose Input/Output |
| GPIO18 | General Purpose Input/Output (PWM0) |
| GPIO19 | General Purpose Input/Output (PWM1) |
| GPIO20 | General Purpose Input/Output |
| GPIO21 | General Purpose Input/Output |
| GPIO22 | General Purpose Input/Output |
| GPIO23 | General Purpose Input/Output |
| GPIO24 | General Purpose Input/Output |
| GPIO25 | General Purpose Input/Output |
| GPIO26 | General Purpose Input/Output |
| GPIO27 | General Purpose Input/Output |
| RUN | System reset pin |
| VREF | Reference voltage for ADC (if carrier board has ADC) |
| I2C0_SDA | I2C bus 0 data line |
| I2C0_SCL | I2C bus 0 clock line |
| SPI0_MOSI | SPI bus 0 Master Out Slave In |
| SPI0_MISO | SPI bus 0 Master In Slave Out |
| SPI0_SCK | SPI bus 0 Serial Clock |
| SPI0_CS | SPI bus 0 Chip Select |
| UART1_TX | UART bus 1 transmit |
| UART1_RX | UART bus 1 receive |
Wiring & circuit basics
Powering the Compute Module 4S requires careful attention as it relies on a custom carrier board for power management. The module itself operates at 3.3V logic levels. The carrier board typically receives a 5V DC input, which is then regulated down to the necessary voltages for the CM4S and its peripherals. It is crucial to use a stable power supply that can provide sufficient current, especially under heavy load. Consult the carrier board's documentation for specific power input requirements and recommended power supply ratings to avoid damage.
When connecting external components, always remember the CM4S uses 3.3V logic. Connecting 5V devices directly to GPIO pins can cause permanent damage. If you need to interface with 5V components, use a logic level shifter. For example, to safely blink an LED, connect a current-limiting resistor (e.g., 220-330 ohms) in series with the LED, and then connect the other end of the resistor to a 3.3V GPIO pin. Connect the other leg of the LED to a GND pin. This ensures the GPIO pin is not overloaded.
For I2C communication with a sensor like a BME280, connect the sensor's SDA pin to one of the CM4S's I2C SDA pins (e.g., GPIO2, which is I2C0 SDA on many Raspberry Pi configurations). Connect the sensor's SCL pin to the corresponding I2C SCL pin (e.g., GPIO3, which is I2C0 SCL). Ensure both the sensor and the CM4S share a common ground (GND). Most I2C sensors also require a 3.3V power supply, which can be sourced from the CM4S's 3V3 pin. Remember to include pull-up resistors on both SDA and SCL lines if not already present on the sensor module.
Programming & getting started
The Raspberry Pi Compute Module 4S, running Raspberry Pi OS (or other Linux distributions), is typically programmed using standard Linux development tools. For embedded applications, you can use languages like Python (with libraries like RPi.GPIO or gpiozero), C/C++ (using the `wiringPi` library or direct system calls), or even MicroPython if a suitable port is available for the CM4S. Development often involves SSHing into the module once it's running on a carrier board, or cross-compiling on a host PC and then transferring the executable.
A common workflow for C/C++ development is to use a cross-compilation toolchain on a Linux host. Install the appropriate GCC toolchain for ARM. Write your C code, compile it using the cross-compiler (e.g., `arm-linux-gnueabihf-gcc your_program.c -o your_program`), and then copy the executable to the CM4S via SCP or by mounting a shared folder. For Python, simply write your `.py` script and run it directly on the CM4S using the `python3` interpreter. For more complex projects, consider using PlatformIO with VS Code, which offers excellent support for embedded development and cross-compilation.