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Make: Electronics Second Edition.   Experiment 11 NO SOUND!

computerhabit

The Experiment is called "Light and Sound".

 

It has you walk through setting up some Transistors to make an LED blink.  Then you swap out some resistors and add a capacitor to make the LED fade out.

 

Then it says:

 

Remove the LED, the 470-ohm resistors, and the 220µF capacitor, and substitute a little loudspeaker, a 100µF coupling capacitor, and a 1K resistor.

 

First, there is no explanation of what a 'coupling' capacitor is compared to a regular capacitor.  I bought a kit so I'm not sure if I'm using the wrong capacitor or not.  There all little cans except for these tiny orange and a blue one which are kind of square and the regular round ceramic capacitors.

 

I get absolutely no sound.  Just a click and a pop sound and only when add power quickly.

 

I thought maybe if I went further with the instructions I'd get something so I completed the build further down where you basically repeat the build above with additional resistors and adding the speaker.  Still no sound!

 

No clue what I'm doing wrong.  I verified the speaker works by testing it with my set of "Snap Circuits".

  • The bit of text in the book you are looking for is this:

     

    "The capacitor blocks the DC component of the signal, while allowing the alternating current through."

     

    It is describing the function/purpose of the capacitor as opposed to its design type.

     

    The breadboard diagram (Figure 2-120) shows an aluminium electrolytic capacitor being used, which matches the preamble text about components.

     

    What is a Coupling Capacitor?

  • in reply to beacon_dave

    Thank you for responding.  I still don't see where my issue is.  Can you at least tell me that you completed this experiment and you got sound?

     

    Honestly I'm thinking there is something missing from the book.

  • in reply to computerhabit

    I've not even read the book - but looking at the page you refer to, it looks like an astable multivibrator circuit initially driving a LED and then driving a small loudspeaker.

     

    First question would be if the multivibrator stage is oscillating.

    Second question would be if the LED is flashing.

    Third question would be if the oscillation frequency is within the audible range of human hearing.

  • For your experiments you can actually do away with the "Coupling" capacitor.

    The only thing it really does is to prevent you leaving the speaker permanently on allowing only pops/clicks! to be passed through.

    You can graduate later to adding the coupling capacitor when it is fully explained that it is acting as a low frequency filter (which is a device to attenuate (turn the volume down on) low frequency signals - like leaving the speaker permanently on.).

     

    To make sound what you need to do is to turn off and on the output pin driving the speaker at the frequency you want.

     

    Here's a bit of pseudo code to help you.

     

    Turn off bit     // Ensure output bit is ready to pop the speaker

    loop:

      Turn on bit     //pop speaker

      wait

      Turn off bit     //reset output bit ready to pop the speaker again

      wait

    goto loop

     

    Have a look at posts on the element14 community for more information.

     

    The challenge after getting the sound to work is to have the sound working whilst simultaneously doing something else.

  • Thank you to all that responded. 

     

     

    I feel kind of silly.  As I was banging my head against the desk the positive wire of the speaker fell off!  The soldering job on the speaker was bad and failed, I guess during testing it worked just long enough for me to think it was good.  I re-soldered the connection and everything worked.

  • in reply to COMPACT

    Thank you for the part about doing away with the coupling capacitor.  That is how I was able to get my first sounds.

  • in reply to beacon_dave

    Thank you.  This reminded me that in the book they mention that replacing the 3.3 uf capacitors with .01 capacitors to move into a frequency you can hear.

  • in reply to computerhabit

    Seems like it always ends up something simple like that I overlooked or a variable that changed along the way for me.  I had a similar issue like that with a speaker not that long ago too! 

     

    Was this from one of the electronics kits/component packs made for the Make: Electronics book?  I was considering getting one for a gift and I was wondering if your issue was from one of the packs.

  • in reply to jpeterson

    Well I ended up buying this one on Amazon which worked out great https://www.amazon.com/dp/B01EKO6FZU

    I realize it was more the buying the parts individually, but I didn't want to deal with that and having everything together in a organized case made it easy to give as a gift anyway.


    P.S. Watch out as I almost made a mistake buying a older kit made by Radioshack for the 1st edition of Make: Electronics and then I saw on Charles Platt's site (http://www.plattkits.com/kits/) that the old kits from radio shack are obsolete and incompatible with Make: Electronics Second Edition and recommends the one by ProTechTrader and one other company.