Core Communication Protocols for IMUs
1. I2C:
I2C (Inter-Integrated Circuit): A two-wire synchronous communication protocol (data and clock) which has multiple devices on the same bus. It is typical in IMUs where space is a premium because it is simple, but lacks the speed of SPI.
2. SPI:
SPI (Serial Peripheral interface): Is a high-speed, full-duplex synchronous protocol. It employs dedicated in and out data lines, a clock, and a chip select meaning it is particularly suited to IMU applications where speed of data transfer is vital.
3. CAN:
CAN (Controller Area Network): The serial bus standard that is robust and developed to work in noisy environments such as industrial systems and vehicles. It is great at inter-linking multiple IMUs and other sensors into a network with very high reliability and error checking.
4. UART:
UART (Universal Asynchronous Receiver/Transmitter): The asynchronous serial and the use of two data lines (TX and RX). It is easy to use in the transmission of IMU data over longer distances to a microcontroller, or to debug data, however, it does not provide a clock signal.
5. RS-485:
RS-485: A standard that outlines some of the electrical specifications of a balanced differential communications network. It supports long-range, multi-drop serial communications, which makes it appropriate in industrial applications in which an IMU is remote to the controller or in an electrically noisy environment.
6. RS-232:
RS-232: A traditional interface specification, Serial communication, that supports only single-ended signaling. It is simple, but easy to noise, it has a short range and is not as commonly used in IMUs anymore because it is replaced by USB, or used in legacy systems.
Data Transmission Process
The process of transmission of motion data sensor to application has a number of steps that are important:
Sensor Data Acquisition
Accelerometers and gyroscopes produce raw data about the relative movement at high rates (usually 100Hz-1kHz).
Data Processing
The raw data provided by the IMU sensors are processed, calibrated, and in some cases pre-processed in the IMU.
Protocol Encoding
The information is transmitted in packages depending on the communication protocols (I2C, SPI, etc.).
Transmission
The data packets get carried across the physical interface to the host processor.
Comparison of Communication Protocols
| Protocol | Data Transfer | Speed(Type) | Distance | Multi-Device | Robustness | Robustness |
|---|---|---|---|---|---|---|
| SPI | Synchronous | High (up to 65Mbps) | Short (0.1m) | Yes (multiple) | Low | High-speed data transfer, sensors |
| I2C | Synchronous | Medium (up to 1Mbps) | Short (0.5m) | Yes (up to 127) | Medium | Low-speed devices, sensors |
| UART | Asynchronous | Medium (up to 115.2kbps) | Short (15m) | Point-to-point | Low | Short-distance communication |
| CAN | Synchronous | Medium (up to 1Mbps) | Long (1.2km) | Yes (multiple) | High | Industrial, automotive, real-time systems |
| RS485 | Asynchronous | Low (up to 115.2kbps) | Long (1.2km) | Yes (multiple) | High | Industrial, long-distance communication |
| RS232 | Asynchronous | Low (up to 19.2kbps) | Short (15m) | Point-to-point | Low | Short-distance communication |
Evolution of IMU Communication Technology
Analog Interfaces
Early IMUs had analog voltages sent out to be converted to digital using ADCs.
Proprietary Digital
There were digital protocols manufacturer-specific and pre standardization.
Standard Protocols
I2C and SPI were introduced and became common in consumer IMU applications in mobile devices.
High-Speed Interfaces
Higher bandwidth at lower power is possible with MIPI I3C and other latest protocols.
Conclusion
To conclude, the communication protocol implemented in the case of IMU application. Explore our MEMS IMU modules and solutions for IMU hardware options can be selected depending on the application, the kind of IMU, and the needs of the system. Typical protocols used are I2C, SPI, CAN and bespoke, with different advantages relating to speed, current draw and complexity.