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Pull-up/down Resistors and Capacitors

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  • Pull-up/down Resistors and Capacitors

    The 1k resistors that I added to my circuits, per the attached, to prevent the firing of an event also firing other unwanted events is not working. Someone suggested adding a 0.1uF capacitor to the circuit, but I do not know where to add them in series with the resistors. On the pull-up circuit, do I add a capacitor after the resistor on the Vin side or before it on the switch side. On the pull-down, add the cap on the gnd side or after the resistor?
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  • #2
    I use a 1uf non polarized capacitor between all inputs and ground on my Arduinos which are essentially the same as the ADIO-100. A 0.1uf would work as well.
    Randy Prade
    Aurora, CO
    Prades.net

    PHLocation - Pushover - EasyTrigger - UltraECM3 - Ultra1Wire3 - Arduino

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    • #3
      Your circuits are correct. What size pull-up/down resistor are you using. A 10k should work, but you can reduce it as low as 1k if you are still having noise problems. Typically a 0.1uF capacitor is big enough, but you can go bigger if needed. A large capacitor and high resistor will cause a slight delay in reaction time when the switch opens because the capacitor has to bleed off through the resistor.

      You should use your NC circuit (rather than the NO) so that the wires running around the house are referenced to ground rather than VIN. Doing so will avoid a variety of ground reference issues that I won't get into here. In your NC circuit, connect the capacitor (if really required) in parallel with the resistor so the capacitor can bleed off when the switch opens. Otherwise you may have a very long delay in response to the switch opening. If you really wanted an NO operation, use the NC circuit and reverse the logic in HomeSeer - IE make a 0 = On, and 100 = Off.

      Noise problems on the inputs are usually caused by:
      - long wire runs between the switch and the ADIO (more than about 25' or so),
      - using non-shielded cable. Shielded cable blocks out RF and other sources of noise. I have some analog runs of shielded cable that are over 100' and run fine without capacitors.
      - cable run close to noise sources such as AC power cables, motors, transformers, audio/video equipment, etc. If they must be close to another cable, cross them at 90 degrees to minimize the magnetic induction from one cable to the other. A sensitive input cable running parallel to an AC power cable for even a couple feet WILL give you noise problems.

      Maybe I should have started by asking what is the exact issue you're having. We may be barking up the wrong tree...

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