Switching between two resistors

Discussion in 'Embedded Systems and Microcontrollers' started by fieryfire, Sep 12, 2018.

  1. fieryfire

    Thread Starter Member

    Feb 14, 2017
    32
    0
    Hello, all,

    I am trying to design a circuit where i want to switch between one resistor network to another. Could you advice me the type of switch i should be using also how will i be able to switch the circuit electronically using a switch.
    I need to switch points A and B to points C and D as shown in the below diagram. But i do not know how i can do this and the type of switch to use. Please Help


    upload_2018-9-12_13-36-27.png
     
  2. DNA Robotics

    Member

    Jun 13, 2014
    364
    140
    This should work.
    You could use a logic level MOSFET and one of your data lines to operate the relay.

    switch points A and B.jpg
     
  3. MrChips

    Moderator

    Oct 2, 2009
    16,745
    5,136
    What are the resistance values of the two resistors?
     
  4. fieryfire

    Thread Starter Member

    Feb 14, 2017
    32
    0
    Thank you very much, I was thinking of a DPDT way to double pole both A and B lines. But its great that it works with SPDT. I dont know why i couldnt see it before. why am i such an idiot...

    Also can you explain or source me to logic level mosfet? I was thinking of using an SPI type SPDT switch to perform the above mechanism.
     
  5. fieryfire

    Thread Starter Member

    Feb 14, 2017
    32
    0
    I would say 348ohm and 348.1Ohm. I need to simulate a trigger for a 350Ohm strain 3-wire quarter bridge
     
  6. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    5,362
    6,288
    A differential of only 0.1 ohms is way too small to be accurately switched using a simple mechanical relay. The relay contacts themselves might have a resistance repeatability higher than that. I'd consider an alternative technique to accomplish what you want.
     
  7. fieryfire

    Thread Starter Member

    Feb 14, 2017
    32
    0
    Would i be able to use the following switch along with standard resistors for this process?

    https://www.maximintegrated.com/en/products/analog/analog-switches-multiplexers/MAX14763.html
     
  8. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    I don't know. The datasheet states that:

    The MAX14759 features 1Ω (max) on-resistance with a ±200nA (max) on-leakage current. The MAX14761/MAX14763 feature 2Ω (max) on-resistance with a ±100nA (max) on-leakage current.

    Again, the key issue here is repeatabitily, it doesn't matter if the switch that you use has a 2 ohm on-resistance, as long as it is always 2 ohms, and not 2.1 or 1.9 ohms, regardless of usage, temperature, and other factors. In all honesty, I don't think those chips can deliver what you want. But that's only my opinion.
     
    OBW0549 likes this.
  9. OBW0549

    Well-Known Member

    Mar 2, 2015
    2,490
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    Instead of switching between a 348.0 Ω resistor and a 348.1 Ω resistor, just leave a 348.1 Ω resistor permanently connected in the circuit and switch a 1.2 MΩ in parallel with it to bring the combined resistance down to 348Ω when the switch is activated. Just about any analog switch or relay should be able to do that, without worrying about contact resistance or ON resistance.
     
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