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  1. #1
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    Touch Switch Schematics-Looking for feedback.

    Hello,
    I have built a High side switch that interfaces with a low voltage relay system
    for home use( existing product) and I am looking for feedback to make the switch safer and more reliable.
    The touch switch that I have built connects to the low voltage relay panel via 3 wires.( Please see attachments)

    • Switch_High
    • Switch_Low
    • Ground


    Switch_High is usually 28~29 VDC.
    The low voltage relay system is designed so that if you touch Switch_High wire
    with the Switch_Low wire the relay built in to the low voltage system will
    toggle on or off.
    Going back to touch switch I made, once the switch is activated by touching it, it will
    momentary forms a connection between the Switch_high and Switch_low as shown on
    the schematics. The Switch will be powered by a separate 12v wall transformer.

    Any feedback is appreciated.


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  2. #2
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    Re: Touch Switch Schematics-Looking for feedback.

    You show several schematics which are disconnected from each other. It is unclear how your project is supposed to operate.

    Does the user bridge his finger across two contacts to activate your project? Is that the purpose of the component labelled 'disconnect pad'?

    Or, does the user touch the floating mosfet gate labelled 'out 2'?

    When I grip my ohmmeter leads with both bare hands, it reads several hundred k-ohms. It will convey a very small signal. Can your detector respond to this level of signal?



  3. #3
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    Re: Touch Switch Schematics-Looking for feedback.

    Quote Originally Posted by BradtheRad View Post
    You show several schematics which are disconnected from each other. It is unclear how your project is supposed to operate.

    Does the user bridge his finger across two contacts to activate your project? Is that the purpose of the component labelled 'disconnect pad'?

    Or, does the user touch the floating mosfet gate labelled 'out 2'?

    When I grip my ohmmeter leads with both bare hands, it reads several hundred k-ohms. It will convey a very small signal. Can your detector respond to this level of signal?
    Thanks for the reply.

    The user touches the S terminal loop ( Buttom Round Pad on the PCB Layout) which causes U2 to sends a high signal (5v) on the 'out' netlabel.
    Resistor R10 is just a place holder no component is soldered there.

    When 'OUT netlabel' is high it turns on Mosfet Q1A which pulls it's drain to ground and also turns on PMOS Q1B.
    Once Q1B is on, terminal Switch_High and Switch_Low become connected causing the low voltage relay system to momentary turn on.
    The resistor divider divides the Switch_High( 29v) in half for the PMOS gate Q1B
    (Max gate voltage is 20v)

    the disconnect pad has a different purpose that is not relevant here



  4. #4
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    Re: Touch Switch Schematics-Looking for feedback.

    Our bodies are good at picking up mains hum. When you touch the input, it will be like sending a 60 Hz sine wave into it. This is likely to cause multiple toggling of your device.

    Do you plan to debounce the input?



  5. #5
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    Re: Touch Switch Schematics-Looking for feedback.

    Quote Originally Posted by BradtheRad View Post
    Our bodies are good at picking up mains hum. When you touch the input, it will be like sending a 60 Hz sine wave into it. This is likely to cause multiple toggling of your device.

    Do you plan to debounce the input?
    This chip is a dedicated touch sensor IC with the processing algorithm built in. The chip itself works flawlessly. My concern is the system as a whole as in safety/reliability.



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