Sensor architecture allows real-time auto emissions monitoring, Pt. 1

Data conversion, storage, and processing and display controllers

Converting analog data to digital format
To enable the sensors’ data to be processed by the MCUs, one needs to convert this data into digital format. ADCs (analog-to-digital converters) can be used to convert the sensors’ output into digital format, making it easier for the processing unit to store and process it.

Given the type of application, one would not require constant or very frequent exhaust-profile data gathering. Therefore, one can easily multiplex various sensors’ outputs on one or two ADCs so that each of them could be sampled one-by-one, therefore, saving the BOM (bill of material) of the solution.

One may also use those intervals when the MCU is not very active or when its ADCs are free to sample the sensors’ output so that effective cost of the overall solution might be reduced. This way, data would be available as and when the core is free to process the data, on a lower priority basis. This way, higher MCU throughput can also be achieved.

For such a system, the overall accuracy of the solution would be heavily dependent upon the sensors accuracy and the performance of the ADCs.

Storage and processing unit
The storage and processing unit also becomes very important for systems which would be catering to this proposed solution on as-and-when-free basis. This approach would require one to have a processor of good processing speed and able to support various MAC (multiply and accumulate)/DSP instructions to quickly manipulate the pool of data required for this solution (which also includes data coming in from the power-train MCU giving the engine loading information).

Another point to note is that the pollution control and monitoring application is an additional feature being extracted out of almost the same already-being-used hardware. Therefore, this application would be sharing its memory space with the already existing applications. As a result, there would be an additional demand for memory to meet all the requirements.

Now adding such functions to the ‘as-and-when-free’ model of the application, one may be required to be more stringent with the access speed of the memory and more liberal with the on-chip memory. A situation may also arise where the on-chip memory is not sufficient for the needs of the overall system. Therefore, depending upon the already existing application requirement of the memory and the size of the data to be stored by the pollution control and monitoring unit, one may require additional amount of memory or interface for external memory along with fast access speed.

Without fast memory access, the whole calculations and report-generation may become a very slow operation. However, techniques like data pre-fetch from such an external memory might be able to overcome such limitations to a reasonable extent.

Display controllers
Display controllers are required to transmit data to the automobile dashboard/cluster so that the driver could take appropriate action. For example, if the pollution increased due to over-loading, the same can be calculated using the data from the power-train MCU and displayed as a flag on the cluster so that loading could be decreased (see below). This visual sharing of information can be achieved in two ways—on-chip display drivers or interfacing this MCU with an external display controller using communication peripherals like I2C, SPI, SCI, Flexbus, Ethernet, USB, etc.


Part 2 of this series discusses communications between the emissions monitoring system and the driver, the sensor array, and future challenges.

References:
1.    Inspection of Car’s Emission Using Infrared Spectrum Technique, M Kong,Z Luo, Y Lu and W j Fan
2.    http://www.vehicletest.state.ma.us/
3.    http://www.implats.co.za/implats/Emission-standards.asp
4.    http://www.theicct.org
5.    http://lh3.ggpht.com/_SHPVwr-0FwA/SdYvlpbGPzI/AAAAAAAAA5s/k0mv_xc08wg/s800/96749.jpg


About the authors:
Ravindra Arora has worked at Freescale Semiconductor as senior design engineer for about six years. He has worked on automotive cluster and safety architecture MCUs. He earned his M.Tech (Instrumentation) from N.I.T Kurukshetra and B.Tech from R.E.C Kurukshetra (India).

Manmohan Rana has worked at Freescale as senior design engineer for about five years. He has worked on memory circuit design, analog and mixed signal design and simulation for various SoC architectures. He earned his BE (Electronics and Communications) from Delhi College of Engineering (Delhi University, India).

Sunil Deep Maheshwari has worked at Freescale as senior design engineer for about five years. He has worked on architectures ranging from motor control, power train, and metering to auto safety. He earned his BE (Electronics and Communications) from Netaji Subhas Institute of Technology (Delhi University, India).

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