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Raise Pin Voltage to headphones With Propeller — Parallax Forums

Raise Pin Voltage to headphones With Propeller

TylerSkylerTylerSkyler Posts: 72
edited 2012-02-02 10:46 in Propeller 1
Hello All! I'm experimenting with propeller and playing wavs through a 3.5mm headphone jack(to headphones). I have the audio playing beautifully, but there is one problem the
audio is really quiet. I believe I need more than the propeller's usual 3.3V in order to get a volume acceptable for practical use. How can raise the voltage output to the headphone jack(pin 10 and 11 go to headphone jack). All help and suggestions welcome and appreciated.

Thanks,
Tyler

Comments

  • CircuitsoftCircuitsoft Posts: 1,166
    edited 2012-02-01 19:37
    Just connect a large (220uF or so) cap between the headphones and ground. They're quiet because the DC offset from the pin is pushing the voice coil out of the magnetic gap and lowering the BL product of the driver.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2012-02-01 19:53
    Tyler,

    It may also help to lower the impedance of your lowpass filter, if you can. What values of R and C are you using?

    -Phil
  • CircuitsoftCircuitsoft Posts: 1,166
    edited 2012-02-01 20:59
    When I've done headphone out, I actually drive the phones straight from the I/O pins with a low frequency high-pass to remove the DC component. The diaphragms themselves are heavy enough for the headphone to physically filter the output.
  • idbruceidbruce Posts: 6,197
    edited 2012-02-01 21:04
    @Tyler

    Are you using an existing object for this project or did you write your own? I had a problem with an existing object that seriously reduced the output. I then tried JonnyMacs sound object and the volume was much louder.

    Bruce
  • idbruceidbruce Posts: 6,197
    edited 2012-02-01 21:09
    @Tyler

    Try JonnyMac's code at this location and see if it helps, http://forums.parallax.com/showthread.php?128129-cylon-eye-sound
  • cavelambcavelamb Posts: 720
    edited 2012-02-01 21:26
    idbruce wrote: »
    @Tyler

    Try JonnyMac's code at this location and see if it helps, http://forums.parallax.com/showthread.php?128129-cylon-eye-sound

    Oh Bruce...
    Thanks for the link to JonnyMacs piece.
    That's a nice bit of work he did there.
    Funny how things work out some times...
    I was just starting to play with the wav objects in the OEX.
    Somehow I had missed his.

    Richard
  • TylerSkylerTylerSkyler Posts: 72
    edited 2012-02-01 21:35
    Thanks for all the responses! I will try to change my project with your suggestions and reply my results.

    Cheers,

    Tyler
  • idbruceidbruce Posts: 6,197
    edited 2012-02-01 21:37
    @cavelamb

    I don't actually believe it is in the OBEX, but it could be.
  • RaymanRayman Posts: 14,845
    edited 2012-02-02 02:58
    Can you really get high volume sound out of a Prop pin? I think you need an external amplifier (but could be wrong).
    You can use powered PC speakers. Or, radioshack sells a little DIP8 audio amp...
  • idbruceidbruce Posts: 6,197
    edited 2012-02-02 04:18
    @Rayman
    Can you really get high volume sound out of a Prop pin?

    Oooooppppsss. I had forgotten that my sound experiments included a LM4808M.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2012-02-02 08:49
    Rayman wrote:
    Can you really get high volume sound out of a Prop pin?
    Theoretically, you could get 125mW peak from a single pin driving an 82-ohm load. But most modern headphones have a much lower impedance than that and would require some series resistance to protect the Prop from overcurrent. Instead, you could use a matching transformer for better power transfer. But an amplifier is the best solution.

    -Phil
  • CircuitsoftCircuitsoft Posts: 1,166
    edited 2012-02-02 10:46
    125mW into a headphone is LOUD. Many cheap MP3 players top out at 10mW into headphones, and they get plenty loud. My 16ohm headphones sound just fine with the circuit I described above. I've even hooked 4ohm speakers up the same way, and they're a bit quiet, but still listenable. Yes, I know that's basically a short to the prop pin, but I don't do it for long, and the chip doesn't get hot.

    You could be lazy and use an OPA2677 as a unity-gain buffer straight from the output pin and have the filtering be done by the speaker itself, or have a filter of 1K/8.1nF and use a cheap amplifier (TDA1517P is nice and can be found in many powered computer speakers) to drive your speakers.
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