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Hardware For Voltage Controlled Switchgear

Discussion in 'General Electronics Discussion' started by Lightning, Feb 16, 2017.

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  1. Lightning

    Lightning

    45
    4
    Oct 12, 2013
    Hello All,

    I am trying to replace some basic switchgear with a homemade Bluetooth controller circuit. The Bluetooth module I have is connected via UART to a microcontroller and the switches I want to control should then be activated from individual digital output pins on the microcontroller.

    The problem I am having is selecting the hardware to do the switching that is controlled from the digital output pins of the microcontroller, essentially I'm looking for a voltage controlled switch.

    Relays have the perfect electrical characteristics but I would like to keep the physical profile small as well.

    I like the idea of using a 4066 bi-lateral switch chip but the R-on seems rather high for a switch (125ohm) and I don't like the idea of messing with the impedance of the connected system too much, as I would like to keep my retro-fit as close to the characteristics of the original switches that I am replacing.

    Some sort of on-chip solid-state relay sounds like a good option but I was wondering if there were any other options that I could consider?

    Any suggestions are appreciated.

    Thank you.
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,014
    2,506
    Nov 17, 2011
    What you have presented is a bit meager. We need more information.
    • Which voltage and currents (AC, DC?) do you need to switch?
    • Do you need isolation (e.g. for safety)?
    • What is the max. size (w*l*h) you can accept? How many channels?
    • What is the max. Ron you can accept?
    Relays come in many sizes, even very small ones.
     
  3. Lightning

    Lightning

    45
    4
    Oct 12, 2013
    Hi Harald,

    Thanks for your rely.

    Yes I can appreciate that, I am just looking to see if there are other methods that I haven't considered.
    • I am working with 12v DC switching, I am unsure of the exact current but it will not be much e.g. 10mA.
    • I shouldn't need any sort of isolation beyond, for instance, a simple plastic cover or the default package isolation.
    • Max size, I am looking for a simple 8 pin DIL through-hole package sort of volume, per channel.
    • I am looking for one channel at the moment to prove my concept but I will be using upwards of five at later iterations.
    • Ideally I am looking to vaguely imitate a normal switch so I think under 10 ohms would be acceptable.
    Yes, I have come across some reed relays since I first posted, that are the sort of size I am looking for. I'm surprised I haven't found any MEMS based ICs, they seem to be all semiconductor based.
    Correct me if I am wrong, I might be looking in the wrong places.

    Thanks.
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    11,014
    2,506
    Nov 17, 2011
    What I meant is isolation between the controlling side and the controlled side, Such as a relay offers inherently.

    You may want to have a look at photomos 'relays', essentially photocouplers with a bi-directional output stage.
     
  5. Lightning

    Lightning

    45
    4
    Oct 12, 2013
    Hi Harald,

    Ah, I misunderstood, I though you meant user-isolation as oppose to circuit isolation. This isn't a requirement of the system, so it gives me a bit more scope as to what I can use.

    I did consider traditional photocouplers, although what you have presented (bi-directional photomos) seems like a good alternative, and looking at some of these datasheets, they have a much lower on-resistance, and a small physical profile to top it off.

    Having considered this it may also be possible to have an LDR based photocoupler if I can find a sensor with enough resistance swing, also giving me a nice linear bi-directional output. I will need to do some more experiments with the system I want to couple to, in order to see if this is possible.

    Thank you for that idea.
     
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