The on-board device, also called probe, contains different components, which are described in this section. You can see the probe PCB in the figure on the right (click to view a larger image).

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Global Architecture

The global architecture of the device is shown in the diagram below.

The Probe Logical Architecture

The main component of the device is its CPU, implementing all the communication protocol functions and on-board data analysis algorithms. The CPU interacts with the local memory (Secure Digital flash card, up to 4 GB), used to store raw and synthesis data, and with a GPRS/UMTS transceiver.

External (discreet) modules such as the GPS receiver are connected directly to the main micro-controller.

The device is interfaced with the EOBD bus using a front-end module, which adapts the electrical signal levels between K-Line and TTL standards.

The power management circuit allows the probe to work correctly in unstable power supply conditions, and manages the power states of the device in relation to the vehicle's duty cycles. The PMC also avoids to drain the vehicle battery by rapidly switching off the probe when the vehicle's engine is shut down.

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Hardware Details

The current hardware configuration includes:

• PIC micro-controller (featuring PIC18F8680 CPU)
  • 8 KB of firmware space
  • 32KB of high-reliable NVRAM (Non-Volatile RAM)
  • 4 independent I/O ports
  • Good computing power
• SD (Secure Digital) card slot
• Connector for GPS module

The device is designed to be cheap and reliable, so that it can be used for monitoring large vehicle fleets at a very low cost.

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Functioning Overview

The device basically cycles the following steps:

1. Poll data from the OBD interface
   • High sampling frequency and accuracy
   • Selective data retrieval
   • Compatibility with a wide range of vehicles
2. Poll data from the GPS receiver (if any)
   • GPS positions retrieved independently
3. Execute analysis routines on-the-fly
   • Statistical data analysis is performed on data blocks (usually every minute)
4. Store data in local memory, and/or
   • High resolution raw data can be stored for later off-line usage
5. Send data to the ground infrastructure
   • GPRS/UMTS network (high coverage)
   • Data encoding to reduce bandwidth usage

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Data Channels

The on-board device is able to read from several data channels (actual channels may vary on different vehicles), but the mostly used are:

1. Odometer
2. Engine speed
3. Engine temperature
4. Air temperature
5. Air mass
6. Ignition angle
7. Injection time
8. Standard engine load
9. Throttle angle
10. Air mass flow
11. Battery voltage
12. Vehicle speed
13. TPS
14. Gear
15. Lambda sensor voltage
16. Negative engine torque (friction torque)
17. Atmospheric pressure
18. Fuel consumption
19. Engine torque
20. Waste gas temperature
21. Catalyst temperature