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What determines sensor speed?

  1. Aug 7, 2017 #1
    What determines the speed of a sensor (keyboard and cameras) transmitting data from the external world (pictures, sound) into the processor (CPU)?
     
  2. jcsd
  3. Aug 7, 2017 #2

    jim mcnamara

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    Staff: Mentor

    Simple answer: it is the rate of data acquisition, usually measured in frames (still pictures) per second. Sound is usually recorded in tandem with each frame in a separate data stream. The cpu on the server can combine the multiple streams into a single digital representation of the data, example: mp3 format.
    Two factors determine upper limits: frame rate and number of pixels/frame - more resolution requires more horsepower on the sensor, its processor, and the data acquisition channel (wire). So it is the total data load on the system.

    Questions like this are general, so the best that can be done is to give a not-perfect fuzzy general answer. Generally there is a trade-off in terms of cost: better quality video costs a lot more. The minimum frame rate has to be faster than human image formation in the eye - probably 24 frames/sec. How good the result looks depends on system quality to a large degree i.e., resolution and frame rate.
     
  4. Aug 7, 2017 #3
    In a word the "interface". More specifically, by "speed" you could mean either the data rate or the latency from the time that an external event happened to the time that the information is available to the CPU.
    Generally speaking, discrete inputs (such as keystrokes or on/off sensors) are polled - so the polling rate needs to be considered. Next, the information is transmitted. Each layer (https://en.wikipedia.org/wiki/OSI_model) of the interface can contribute to latency. In particular, layer 4 usually requires the servicing of a CPU interrupt - and that can be delayed by the interrupt priority and CPU loading.
     
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