Both STM32 and ESP32 are popular 32-bit microcontroller units (MCUs) used in many Internet of Things (IoT) applications today. When choosing between them for a new project, developers must consider factors like processing power, memory, peripherals, ecosystem support, cost, and more. Overall, STM32 tends to be the better choice for most applications due to its superior performance, larger ecosystem, and lower cost.
Processing Power
The STM32 family uses ARM Cortex-M cores ranging from Cortex-M0 to Cortex-M7, while ESP32 uses dual core Tensilica Xtensa LX6 cores. The fastest Cortex-M7 core in STM32 runs at 400 MHz, while ESP32 LX6 cores run at 240 MHz. So in terms of raw clock speed, STM32 has an advantage. Cortex-M cores are also more power efficient than LX6 cores, giving better performance per watt.
Real world benchmarks show STM32 performing 1.2x to 5x faster than ESP32 on most tasks. Only when running specialty workloads optimized for ESP32 does it match or outpace STM32 speeds. Since most software is written for Cortex-M, STM32 maintains a significant performance lead over ESP32 in typical usage.
Memory
STM32 MCUs range from 32 KB to 2 MB of flash memory, and from 6 KB to 1 MB of RAM. ESP32 has 520 KB RAM and 448 KB ROM. So for storage, ESP32 has a decent amount of RAM but very little flash to store code long term. STM32 offers much more flexibility with larger flash capacity options.
For processing memory, ESP32 gives you more RAM to work with. But thanks to the better efficiency of Cortex-M cores, STM32 can make do with less RAM than ESP32 for most workloads. Only for complex apps processing large amounts of realtime data does ESP32’s extra RAM deliver a benefit.
Peripherals
Both STM32 and ESP32 have a rich set of integrated peripherals, including GPIO, ADC, DAC, timers, UART, I2C, SPI, etc. STM32 generally offers more flexibility and control with up to 140 I/O pins vs 40 pins on ESP32, more advanced timers, multiple ADCs and DACs, hardware encryption acceleration, and other extras.
A key difference is STM32 also often adds specialized peripherals targeting specific application areas. For example, some MCUs have integrated USB, Ethernet, LCD controllers, or advanced motor control circuitry. ESP32 peripherals are more generic, requiring external components for specialty interfaces.
Ecosystem Support
As one of the most popular embedded architectures for over a decade, ARM Cortex-M benefits from strong third party support. There is a vast selection of IDEs, compilers, debuggers, libraries, drivers, code examples, middleware, RTOSes, and other software for Cortex-M and STM32 MCUs.
ESP32 uses the less mainstream Xtensa architecture and has a smaller following. The ESP-IDF framework gives good GPIO, WiFi, and general purpose C/C++ support. But for added functionality, engineers spend more time building versus leveraging existing libraries and tools. The ESP32 ecosystem is also less stable, with rapid framework changes breaking compatibility.
Cost
Across their numerous product lines, STM32 MCUs range in price from under $2 to over $20 per unit. ESP32 modules cost $2 to $10 at volume. So both families offer low cost options, though ESP32’s minimum pricing is slightly lower.
However, STM32’s pricing advantage grows when considering BOM cost. ESP32 is sold exclusively as a module requiring additional components like a crystal oscillator and flash memory chip. STM32 MCUs integrate these features to give a simpler, smaller overall solution cost.
Lastly, STM32’s lower power usage can reduce operating costs, especially for battery powered devices where energy efficiency is critical.
Use Cases
With its combination of excellent performance, rich features, and low cost, STM32 can fit into almost any embedded application. It works very well for mainstream MCU use cases like:
- Industrial automation and motor control
- IoT and wireless sensor nodes
- Consumer electronics and appliances
- Medical and wearable devices
- Mobile accessories and audio products
ESP32 shines for WiFi-centric applications. Its on-chip WiFi and adequate processing are a perfect match for projects like:
- Connected home products
- WiFi-enabled toys and gadgets
- Mesh network nodes
- IoT gateways and hubs
For the many embedded projects requiring general purpose compute with flexible I/O, but not WiFi, STM32 is usually the superior choice over ESP32.
Development Experience
Engineers comfortable working in C/C++ will feel right at home developing on STM32 and ESP32. Both can be programmed directly via GPIO or through a debug probe, and both work well with IDEs like Eclipse, IAR, Keil uVision, etc.
STM32 is better supported by more IDEs and also benefits from MDK, a full featured IDE from ARM specifically optimized for Cortex-M development. ST also provides the STM32CubeMX config tool which makes setting up new projects very fast.
The biggest difference is ESP32 relies heavily on Espressif’s ESP-IDF framework. This gives useful libraries and abstraction but also forces you into their framework rather than programming directly to hardware as you can with STM32. The frequent updates to ESP-IDF can cause breaking changes in existing code.
Conclusion
While ESP32 is a worthy low cost microcontroller for select applications, primarily those requiring WiFi, STM32 based on Cortex-M offers superior performance, features, and ecosystem support for the vast majority of embedded projects. With STM32 you get great compute power, plentiful memory, abundant peripherals, rock solid stability, and tremendous design flexibility.
Unless WiFi and wireless connectivity are must-have requirements, STM32 MCUs will almost always be the better choice over ESP32. The STM32 family’s combination of excellent ARM processing with industry leading low power and a huge selection of options makes it a hard to beat microcontroller solution for demanding IoT applications.
