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I have a question on a simple 555 buzzer circuit.

  1. May 9, 2013 #1
    I plan to take a 555, wire it up into astable operation to make a square wave, and hook the output up to a transducer. It's Panasonic's 24C411, with a rated voltage of 15V peak-to-peak and a maximum current of 2mA. Apparently, the maximum output current of the 555 is 200mA, and a 9V can put out between 100mA and 200mA at the highest. I'd like to simply use a resistor, but would that just draw too much of the voltage?

    On the other hand, perhaps it would be better to use a speaker. I just remembered that I have a small one lying around.
     
  2. jcsd
  3. May 10, 2013 #2
    The Panasonic 24C411 appears to be a piezo, which means it's mostly capacitive, so you probably don't need a limit resistor at all. But you could experiment to see how loud things get with, say, 100 ohms...
     
  4. May 12, 2013 #3
    Thank you! That's what I thought at first, but then the mention of a current limit made me unsure. I've got a potentiometer, so I can try it gradually, too.
     
  5. May 13, 2013 #4
    I tried it with a 100 ohm resistor and then with nothing, to no avail either time. Then I tried with an 8 ohm speaker, and it made a small pip upon being connected and then again upon being disconnected, as if it were high all the time. I wish I had an oscilloscope so I could tell if that's actually the case. For the time being, what do you think?
     
  6. May 13, 2013 #5

    NascentOxygen

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    Try coupling to the speaker via an electrolytic capacitor, say 100uF, with its + terminal going to the 555's output. A 25V or higher rating will be fine.

    To test whether the 555 circuit is actually oscillating, you could temporarily connect a larger capacitor across its timing capacitor, making the period quite long, then power a LED from the output (in series with a 4.7k resistor) to see whether the LED blinks.
     
  7. May 13, 2013 #6
    Also as a 555 no-oscillate test you could check the output voltage with both DC and AC settings on a multimeter to see if there is any difference. Zero AC volts and your one-click speaker would indicated that the chip is not oscillating...
     
  8. May 15, 2013 #7
    I have a very rudimentary multimeter; it won't check AC voltages this low. I considered that the 555 might be busted by static, so I tried with a Wein bridge oscillator - no good there either. However, I know for a fact that the LM741 I'm using is working. That's only supposed to put out 25 mA - maybe that's not enough.

    I like NascentOxygen's idea with the LED - unfortunately, I'm just starting with electronics and actually don't have any. I'll keep trying, but I really don't know what's wrong...
     
  9. May 15, 2013 #8

    NascentOxygen

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    Staff: Mentor

    So the coupling capacitor gave silence?
     
  10. May 16, 2013 #9
    You can use your DC meter instead of an LED for the NOx long-period test. You can also use the DC setting to "look at" a higher frequency AC, especially one that swings between 0 and +V, because it will try to average the signal and thus show a lower than +V reading -- if there is any oscillator activity.

    555's are not very static sensitive, although you may destroy them by reversing the supply lines. I don't remember offhand if I've ever outright killed any while putzing around with them. I would double check that you have everything connected like this (where you can use your meter -- to + or - -- instead of the LED):
    http://static.electro-tech-online.com/imgcache/8016-555schematic.gif

    And I would investigate getting a good multi-meter, even a $10 one should have some low voltage AC facility...

    Also, don't give up hope. Things will (suddenly) start to work (for no apparent reason)!
     
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