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AutoPi TMU CM4 vehicle telematics unit with OBD-II connector
AutoPi Technical Guides

AutoPi TMU CM4 Deep Dive: Open-Platform Vehicle Telematics for Indian OEMs

GSAS Engineering · · 7 min read

What Makes the TMU CM4 Different

Most vehicle telematics devices on the Indian market are closed black boxes. They extract a fixed set of OBD-II parameters, push data to a proprietary cloud, and give fleet operators a dashboard with limited customisation. If the standard parameter set does not cover what an engineering team needs, raw CAN frames, custom DBC decoding, edge-side data processing, the device cannot help.

The AutoPi TMU CM4 takes a fundamentally different approach. Built on the Raspberry Pi Compute Module 4 (Broadcom BCM2711 quad-core Cortex-A72 at 1.5 GHz), the TMU CM4 runs a full Debian Linux environment with SocketCAN, Docker, Python, and SSH access. It is a general-purpose embedded computer that happens to have automotive-grade OBD-II and dual CAN-FD interfaces, 4G LTE connectivity, multi-constellation GNSS, WiFi, Bluetooth 5.0, a 6-axis IMU, and a smart power manager, all in an OBD-II dongle form factor.

Hardware Architecture

The TMU CM4 ships with 1 GB LPDDR4 and 8 GB eMMC in the base configuration, upgradeable to 8 GB RAM and 32 GB eMMC for workloads that require more headroom. Two independent CAN-FD interfaces operate via SocketCAN, providing raw frame access to every CAN ID on the bus. The multi-constellation GNSS receiver (GPS, GLONASS, BeiDou, Galileo, QZSS) with assisted GPS delivers sub-metre positioning accuracy.

A 40-pin HAT expansion header accepts accessory boards, including AutoPi’s DoIP HAT for Ethernet-based vehicle diagnostics, and provides GPIO, SPI, I2C, and UART for custom sensor integration.

The Smart Power Manager (SPM) handles vehicle power management autonomously. It monitors battery voltage, manages ignition-off sleep modes, and wakes the CM4 on configurable triggers, CAN bus activity, accelerometer movement, or scheduled timers. Input voltage range of 12.5 to 35 V DC covers passenger cars through heavy commercial vehicles and construction equipment.

Key Specifications

FeatureSpecification
ProcessorBCM2711 Cortex-A72 quad-core @ 1.5 GHz
Memory1 GB LPDDR4 (up to 8 GB)
Storage8 GB eMMC (up to 32 GB)
CAN2x CAN-FD via SocketCAN
OBD-IIStandard PID polling + custom protocols
Cellular4G LTE Cat 4 with 3G fallback
GNSSGPS/GLONASS/BeiDou/Galileo/QZSS
Sensors6-axis IMU (accelerometer + gyroscope)
Expansion40-pin HAT, 2x USB, Gigabit Ethernet, micro HDMI
Power12.5–35 V DC, Smart Power Manager
Sampling100 samples/sec with microsecond timestamps

Edge Computing on the Vehicle

The Docker runtime on the TMU CM4 enables containerised workloads running directly on the device. This is where the platform diverges most sharply from conventional telematics hardware. Instead of transmitting every raw CAN frame over cellular, which is expensive on Indian LTE data plans and impractical for high-frequency signals, engineers deploy edge containers that filter, aggregate, and process data locally.

Practical edge computing use cases for Indian deployments:

  • Data reduction: aggregate 100 Hz CAN signals into 1 Hz summaries before cellular upload, reducing data costs by two orders of magnitude
  • Anomaly detection: run threshold checks on engine coolant temperature, oil pressure, or battery voltage and transmit alerts only when anomalies are detected
  • DBC decoding: import manufacturer-specific DBC files to decode proprietary CAN signals on-device, transmitting decoded engineering values instead of raw frames
  • Local logging: store weeks of high-resolution data on the eMMC for later retrieval via WiFi, useful for R&D field testing where cellular coverage is intermittent

AutoPi Cloud: Fleet-Scale Management

The AutoPi Cloud platform provides device management, OTA firmware updates, and data visualisation for fleet deployments. Device provisioning, configuration changes, and Docker container deployments push over-the-air to individual devices or device groups. The cloud dashboard presents trip data, geofencing, driver behaviour scoring, and vehicle health metrics. REST APIs enable integration with existing fleet management platforms and enterprise ERP systems.

For Indian fleet operators managing hundreds or thousands of vehicles across states with variable cellular coverage, the combination of edge processing and cloud management means the system continues logging data during connectivity gaps and syncs automatically when coverage resumes.

Applications in India

  • Commercial fleet operators: fuel consumption analysis, driver behaviour scoring, maintenance scheduling across truck and bus fleets
  • Automotive OEMs and R&D: field data acquisition for warranty analysis, product validation, and durability testing on Indian roads
  • EV fleet management: battery SoC monitoring, charging session logging, thermal management data for electric vehicle fleets
  • Agricultural equipment: tractor and harvester operational data for precision agriculture deployments
  • Two-wheeler fleet pilots: delivery and ride-sharing fleet monitoring with compact OBD-II form factor

Why Buy AutoPi from GSAS

GSAS Micro Systems is the authorised AutoPi engineering partner in India, providing local stock, INR invoicing, CAN bus integration guidance, custom DBC file development support, and AutoPi Cloud onboarding assistance. Engineering teams in Bengaluru, Hyderabad, Chennai, Pune, Mumbai, Delhi NCR, and Visakhapatnam can request evaluation units for proof-of-concept projects.

Explore the AutoPi TMU CM4, CAN-FD Pro, and AutoPi Mini on our product pages, or contact us for technical consultation and volume pricing.

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