Signal on Sensor Array

Discussion in 'The Projects Forum' started by nafn, Feb 18, 2011.

  1. nafn

    Thread Starter New Member

    Feb 18, 2011
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    Hi all!
    I have one question to ask. The situation is like this;

    There are four outputs (unit is in volt) generated by four sensors. It is expected that each output will have different voltage value. Is it possible to build OR is there any circuit that can pick up the highest voltage value out of four ouputs without changing the real output signal? I don't want to do it in the digital domain.

    So far, i just found the so-common voltage comparator; comparing 2 inputs but it will output kind of logic state; which is not within my requirement.

    Please, could anyone here shed some light regarding my question.
    Many thanks in advance!
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    A microprocessor can convert each sensor voltage and keep the largest value.

    You say you don't want to go digital, but how do you evaluate voltages and keep just one? In what form can you store the voltage value?

    You might give a lot more detail about what you are trying to do.
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,120
    3,046
    What would be the point to "pick up the highest voltage" and not change the output? Do you mean you want to pass the highest voltage from 1 of 4 sensors to the output of the requested circuit? You need to specify the voltages you are talking about and the impedance of the sensor outputs (in terms of what they can drive without being overloaded).
     
  4. nafn

    Thread Starter New Member

    Feb 18, 2011
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    Hi beenthere!
    Tq for your quick respond. Currently, I'm doing a sensor array for ppg signals. I have four I-V circuit correspond to four photodiodes (PD). The signals are being picked up from a large portion area but will have different output voltages.
    Previously, I did some simulation using optical software and the results show that each PD will output different intensity and hence, will give different voltage output at I-V circuit.
    I plan to eliminates complex signal processing, be it in analog form nor in digital form. But I'm not sure, if this is possible.
    Hope to hear your feedback. Feel free to ask if my point is not clear to you.
     
  5. nafn

    Thread Starter New Member

    Feb 18, 2011
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    0
    Hi wayneh!

    Yes, I intend to pass the highest voltage from 1 of 4 sensors and feed it to the next stage of signal processing. By doing this, I think; will help to make the signal processing much simpler. The voltages that I mention are referring to the PPG signals output from I-V converter.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,120
    3,046
    I have no idea what that means. Numbers please.
     
  7. John P

    AAC Fanatic!

    Oct 14, 2008
    1,634
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    Sure, it's easy.

    Each sensor drives an op amp set up as a voltage follower, with a diode in the feedback loop. The outputs (at the cathode side of the diodes) are all connected together. The highest input will appear at the output.
     
  8. nafn

    Thread Starter New Member

    Feb 18, 2011
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    0
    Hi John P!
    Thank you for your idea!:)
    However, I have one thing to ask. Correct me if I'm wrong, the voltage follower with a diode as a feedback should be placed right after the Photodiode or after the I-V converter?:confused:

    Looking forward to hearing the feedback from you!:)
     
  9. nafn

    Thread Starter New Member

    Feb 18, 2011
    5
    0
    Hi again!
    I've tried to simulate the voltage follower with a diode in the feedback loop. I tried both inputs; AC and DC signal. When I applied the DC signal, the output from the cathode diodes shows the average value instead of showing the highest output. What I mean is that; if Vin1=3V and Vin2=2V; the Vout=2.5V.
    Then, when I simulate the circuit using AC signal, the output signal will be clipped at the negative cycle, or I can say that the output become half-wave rectifier.
    I'm in doubt whether this circuit config can do like I need when looking at the simulation results but that's not mean that I fully trusted the simulation method; in anyway, this method is quite useful.

    Actually, the signals from the sensor will have both AC and DC components. I'm lost now :(...huhu...
     
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