Small project - adjustable buzzer volume

Discussion in 'The Projects Forum' started by prv, Apr 17, 2013.

  1. prv

    Thread Starter New Member

    Apr 17, 2013
    3
    0
    Hi,

    I need to build an alert panel that emits a sound when a 12v supply is applied to it. The slight wrinkle is that the volume needs to be adjustable, from "gently attract the attention of someone on watch, while not waking others sleeping nearby" to "WAKE UP RIGHT NOW!" and anywhere in between. The adjustment would be performed manually using a rotary knob - I already have the laser-cut front panel so this form of interface is fixed.

    I thought this would be really simple, barely a circuit at all, just put a variable resistor in series with a 12v buzzer. In fact, as you no doubt already know, standard piezo buzzers don't work like this, they need a certain minimum voltage to start vibrating at all, and then when they do get going it's at almost full volume, no scope for adjustment.

    So how would you suggest I make this? I'm really looking for simple, minimum part count - so if the answer is "just buy one of XYZ type buzzers, they can be adjusted with a pot" then that's great. Otherwise I assume I need a circuit that generates a tone, and I can put my pot between that and a small speaker. The panel space is pretty small, as I was only expecting to be mounting a pot and a buzzer, so any pointers on small speakers would be handy if going this route.

    My level of electronics knowledge is "rusty school physics", so although I'm quite happy soldering stuff together I'm not really up to designing an analogue circuit based on general pointers - my apologies, but I'd really need a diagram to work from.

    (For general interest, the application is a below-decks warning panel for use on my boat at night, at sea. Depending on the configuration of another, off-the-shelf piece of kit, it might be set up to warn that a ship has been detected a long way off, that a ship is coming close enough that we need to take action, that a lone watchkeeper has fallen overboard, or (if in harbour rather than at sea) that the anchor is dragging. These different uses, together with the differing combinations of people who may be on board and on watch vs asleep, lead to the requirement for adjustable volume. Happy to answer general-interest questions about this, but don't really want to get into debating the requirements.)

    Thanks in advance for any help you can give,

    Pete
     
  2. #12

    Expert

    Nov 30, 2010
    16,278
    6,791
    I hope somebody can point to an adjustable alarm for 98 cents, but meanwhile, This sounds like a job for a 555 timer and a tiny speaker.

    http://www.allaboutcircuits.com/vol_6/chpt_6/7.html

    The 1 Meg resistor seems wrong to me. I say, use 10,000 ohms.
    Eliminate the 510 ohm resistors and the LEDs.
    Use a capacitor to connect the signal to a volume control.
    Add a speaker.

    This circuit will present a short duty cycle square wave to the speaker, making a rather annoying sound. If you can accept this approach, we can calculate values for you.
     
  3. Mitch conrad

    New Member

    Apr 10, 2013
    7
    2
    I also might want to put a op-amp with that 555 buzzer. I have one set up on my bread-board with a pot and the sound is not all that loud with a 9v power source.

    It's makes a rather obnoxious sound at low frequencies(1 to 4Hz).
     
  4. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    I can't suggest an electronic solution to this. My advice, failing all else, is to add a baffle of sorts over the speaker. This is the only way I've found to control the volume of a piezo/buzzer. Some manufacturers sell baffles for their piezos.

    You could add a plastic cover of sorts as well. I'm picturing an 1/8" thick piece of plastic cut in a circle centered over the piezo (assuming it is behind a panel). Then a screw fastens one edge of the circle and it can be swiveled to cover the piezo to control the volume. Not sure how well this would work, just a thought.
     
  5. prv

    Thread Starter New Member

    Apr 17, 2013
    3
    0
    To be clear, I'm not trying to reduce the volume of the piezo buzzer I have. I am trying to build an alternative to it.

    Pete
     
  6. prv

    Thread Starter New Member

    Apr 17, 2013
    3
    0
    A small chip, two resistors, and a capacitor? I think I can manage that :). Thanks. The fact that it natively runs at 12 volts is handy too. Although note this is "nominal" 12v, like in a car - it could be up to maybe 14.4v when the engine is running - likely to be a problem?

    I'm not sure what you meant by "Use a capacitor to connect the signal to a volume control" though.

    When you say "an annoying noise" - how annoying are we talking about here? :) I'm hoping for something relatively high pitched, a beep rather than a growl, as the latter may not be recognised as an alarm and could also perhaps be masked by engine noise if motoring rather than sailing.

    Thanks,

    Pete
     
  7. #12

    Expert

    Nov 30, 2010
    16,278
    6,791
    Yow! Problem. Charging systems are electrically noisy and tend to shoot spikes through integrated chips. You will need to add parts to keep the timer safe.

    Most 555 chips run at 15 volts and the protective circuit can help guarantee that.

    Pin3---capacitor---volume control-----speaker.

    The frequency is entirely adjustable with resistors presently labeled, 1M and 100k. You can even throw away the 100k resistor put a pot in where the 1M resistor is to make it adjustable.

    NE555 = 15V and outputs +/- .2 amps
    TLC555 = too weak of an output
    LM555 = 18V and outputs +/- .2 amps
    ICM7555 = 18V and too weak of an output current.

    Something like this, and maybe other people here can suggest improvements.
     
    Last edited: Apr 18, 2013
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