OBD Accessory Controller Using CAN and Battery State Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Determining the operational state of a vehicle has become unreliable due to advancements such as 'smart alternators' and hybrid powertrains, making it difficult to provide power to vehicle accessories only when the vehicle is operational without excessive battery drain or interference with vehicle communication systems.
Innovation Solution
An accessory controller that monitors both the CAN voltage and battery voltage through the OBD2 port to accurately determine the vehicle's operational state, providing power and mode signals to accessories like dashcams based on these parameters, minimizing power consumption when the vehicle is not in use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If battery voltage monitoring is used to determine vehicle operational state, then the system can detect when the vehicle is running (higher voltage indicates alternator charging), but smart alternators and hybrid powertrains make voltage levels unreliable for determining operational state
Solution Approach 1:
The system segments the operational state detection into multiple independent monitoring channels: CAN bus communication state monitoring and battery voltage monitoring. Each channel provides independent data about vehicle operation, and their combination resolves the unreliability of using either channel alone. The CAN bus state indicates whether the vehicle's communication network is active, while battery voltage provides complementary power system information.
Solution Approach 2:
The OBD2 port is utilized as a multi-functional interface that simultaneously provides both CAN bus communication access and battery voltage measurement capability. This universal interface allows the accessory controller to extract multiple operational indicators from a single standardized connection point, eliminating the need for separate sensing mechanisms.
2Ease of operation
If power is provided to accessories when the vehicle is operational, then accessories function properly during vehicle use, but determining operational state becomes complex with multiple monitoring parameters
Solution Approach 1:
The accessory controller serves as an intermediary device that consolidates multiple monitoring functions (CAN bus state detection, battery voltage measurement) and translates them into a single operational decision output. This intermediary approach simplifies the overall system architecture by centralizing the complexity within a dedicated control unit rather than distributing it across multiple components.
Solution Approach 2:
The system performs preliminary monitoring and evaluation of both CAN bus state and battery voltage continuously before making power delivery decisions. This preliminary action allows the accessory controller to be fully prepared to immediately enable or disable accessory power based on the current operational state without delay or complex real-time computation.
3Measurement precision
If the accessory controller monitors both CAN voltage and battery voltage, then accurate determination of vehicle operational state is achieved, but power consumption increases
Solution Approach 1:
The accessory controller implements periodic monitoring of CAN bus state and battery voltage rather than continuous high-rate sampling. The controller checks these parameters at appropriate intervals sufficient to detect vehicle operational state changes while minimizing unnecessary power consumption during stable operating conditions.
Solution Approach 2:
The accessory controller leverages existing vehicle system activities to reduce its own power consumption. For example, it monitors CAN bus communication by listening to existing traffic generated by vehicle systems rather than actively probing or transmitting test signals. Similarly, it measures battery voltage using the existing electrical system infrastructure.
4Loss of energy
If power is delivered to accessories based on operational state, then battery drain is minimized when vehicle is off, but false operation states may trigger incorrect power delivery
Solution Approach 1:
The accessory controller uses feedback from both CAN bus state and battery voltage measurements to continuously verify the inferred operational state. The dual-parameter feedback mechanism allows the controller to cross-validate its determination of vehicle operation, reducing the likelihood of false state detection and incorrect power delivery decisions.
Solution Approach 2:
The system incorporates hysteresis and threshold buffering in its operational state determination logic to prevent rapid switching or false triggering near boundary conditions. By establishing cushioning margins around the transition thresholds for CAN bus state and battery voltage, the system avoids premature or incorrect power delivery decisions that could occur with noisy or marginal signal conditions.
Data Source
AI summary
An accessory controller is configured for installation in a vehicle including a vehicle battery, an on-board diagnostics (OBD) port, and a vehicle accessory. The accessory controller includes a network input configured for connection to a communications network pin of the OBD port, and a battery input configured for connection to a battery pin of the OBD port. The accessory controller further includes a controller circuit configured to deliver a vehicle operation signal to the vehicle accessory when a communications signal provided via the network input exceeds a first voltage threshold and a battery signal provided via the battery input exceeds a second threshold.