Connect with us

Optoisolator

Discussion in 'General Electronics Discussion' started by Galgenstrick, Oct 19, 2015.

Scroll to continue with content
  1. Galgenstrick

    Galgenstrick

    3
    0
    Oct 19, 2015
    I would like to know how to take the AC voltage supplied from a doorbell (usually 8-24VAC) and turn that into a 5V DC signal I can use as an digital input to an Arduino Uno. Is this something that can be done with an optoisolator or relay? I would like 5V DC supplied every time the doorbell is pressed and it to work regardless of the AC voltage the doorbell supplies, as long as it's in the 8-24V range.

    I am making this project as a gift, so I cannot measure the exact AC voltage the doorbell supplies, I just know it will be between 8 and 24V.
     
  2. Alec_t

    Alec_t

    2,949
    803
    Jul 7, 2015
    If the AC bell supply can share a common ground with the Arduino supply the all you need is a resistor and zener diode to act as a voltage divider-cum-regulator.
     
  3. Galgenstrick

    Galgenstrick

    3
    0
    Oct 19, 2015
    Wouldn't that just be a clipper circuit? I need 5V DC for the digital input.
     
  4. cjdelphi

    cjdelphi

    1,096
    104
    Oct 26, 2011
    But the ac will give you pulses ... maybe rectify it pass it through a cap and a bleed resistor depending on current, maybe a transistor and a 7805.. depends on the AC current to determine resistor values...
     
  5. GPG

    GPG

    452
    66
    Sep 18, 2015
    Use a bridge rect (4 1N4148 will do) and a 1.8K resistor to feed the diode of an optocoupler Use 10μF across the output of the bridge if pulsing output is not manageable. On the transistor side use 100K load either in the collector to 5V or the emitter depending on the polarity of the signal required. A 4N25 or similar will do.
     
    Last edited: Oct 20, 2015
  6. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    Jeff,
    What is the current your Arduino Uno + every thing it drives requires?
     
  7. AnalogKid

    AnalogKid

    2,496
    718
    Jun 10, 2015
    An AC-coil relay with an 8-24 V guaranteed pull-in range will be hard to find; better to go with an opto. I recommend *not* trying to combine the doorbell-side and Arduino-side grounds. A 4N35 has a minimum CTR (current-transfer ratio) of 100%, which more than enough to saturate the output transistor over the full input range. But if the output is not pulling low enough, increase R2 to 10 K. Also, you can move R2 to the emitter side of the output if you want positive-going pulses.

    This circuit makes 60 Hz pulses, not a DC level, when the doorbell rings. While it is fairly simple to add a missing-pulse detector to turn the opto output into a level, it is easier and cheaper to do that in Arduino firmware.

    ak
    DoorbellInterface-1-c.gif
     
    Last edited: Oct 20, 2015
    davenn and BobK like this.
  8. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    I would second AnalogKid's solution.

    Bob
     
  9. Galgenstrick

    Galgenstrick

    3
    0
    Oct 19, 2015
    Thanks. I'll try that out!
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-