Propeller controlled doorbell

I'm looking to use a propeller to control a doorbell through an uln2003. I'm going to running the doorbell solenoid at 12v...will the uln2003 provide enough protection between the the solenoid and the propeller chip?

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  • JonnyMacJonnyMac Posts: 5,870
    edited October 10 Vote Up0Vote Down
    It will be fine if what you're driving meets the current rating of the ULN. At EFX-TEK, we have a Propeller-base controller than uses the ULN2803 as the output driver. Make sure that you connect the doorbell to the output such that the internal flyback diodes can work. It is okay to gang channels together; we've done that a couple times with our little controllers that have ULNs on the outputs.

    Do keep in mind that the ULN2x03 has about a 1.4v drop from ground to collector; this may affect your output.
    Jon McPhalen
    Hollywood, CA
    It's Jon or JonnyMac -- please do not call me Jonny.
  • We use a 3.3 Volt relay from omron (G6KU-2PY 3DC) (=33mA of the max 40mA/pin )
    Try to find the model with highest solenoid resistant
  • Perhaps it's because I'm old, but I'd be nervous about attaching any relay directly to an IO pin -- I'd toss in an n-channel FET to switch the load.
    Jon McPhalen
    Hollywood, CA
    It's Jon or JonnyMac -- please do not call me Jonny.
  • At the very least you'll need some shottky's to protect the pin's protection diodes, and be sure
    the 3V3 supply has enough decoupling that kick-back doesn't raise its voltage excessively.

    A dual MOSFET + diodes + bistable relay can work quite well, I've used this in a circuit running from
    1.5mA total at 12V+, you need enough capacitance to hold up the rail during the bistable relay
    pulses, and run microcontroller slow.
  • I like JonnyMac's solution, however you could use a TIP120 and isolate the Solenoid voltage from the Propeller and use a GPIO from the Propeller to drive the base of the TIP120 separated by a 1K resistor. Adding a 5 volt regulator would give you the voltage for the Propeller from the solenoid voltage. Using something like a 1N4001 diode across the solenoid would be a good idea as well.
  • Relays or monster TIP120s are totally unnecessary. The ULN2x03 will be fine but remember that it has a high Vce(sat) of around >1.5V since it is based on Darlingtons and really the ULN2xxx series were designed for pulsed outputs and so the outputs have to be derated if you try to run one output at a high current continuously (RTM). I haven't bothered with using these chips for many years now as it is more convenient to use discrete digital transistors with very low Vce(sat) so they are very efficient but there are also MOSFETs in small SOT23 packs that can handle a few amps too. Of course you don't need to use such small packs but by way of comparison even these little beasts are more rugged than the transistors in the ULN2x03 part. Don't forget to use a diode across the coil, the more direct and closer the better.
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  • tonyp12tonyp12 Posts: 1,872
    edited October 10 Vote Up0Vote Down
    A doorbell like pictured below?
    They use 16volt (10w) transformer, so it's pretty low voltage.

    Are you using 16VAC?

    If DC, you could use a mosfet.
    A 50cents MCU could power a nmosfet-solenoid-driver on the low-side, like this one:
    http://www.mouser.com/ProductDetail/ON-Semiconductor/NUD3124LT1G/?qs=sGAEpiMZZMshyDBzk1/WizSW%2bwlCH/hM25spW3xjdko=
    Internal Zener Eliminates Need for Free−Wheeling Diode.

    366 x 284 - 34K
  • If you are referring to a doorbell, then why not use a speaker and tiny amp IC, and drive from an audio file in the prop. Ie a musical doorbell.
    Else are you referring to an electronic lock.
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  • Cluso99 wrote: »
    If you are referring to a doorbell, then why not use a speaker and tiny amp IC, and drive from an audio file in the prop. Ie a musical doorbell.
    Else are you referring to an electronic lock.

    I think it's the classic electric striker "ding dong" type which some people prefer.

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  • Thank you for all the replies...tonyp12 that is the correct doorbell. This forum is amazing. You guys rock. Thanks again
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