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Amplify 600mv-need help? — Parallax Forums

Amplify 600mv-need help?

computer guycomputer guy Posts: 1,113
edited 2010-04-26 01:57 in General Discussion
Does anyone have a schematic for amplifying 600mv into at least 1.5v?


Thank you smile.gif

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Comments

  • Brian218Brian218 Posts: 92
    edited 2008-10-22 08:54
    Check this site out:
    http://www.satsleuth.com/schematics.htm

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  • LeonLeon Posts: 7,620
    edited 2008-10-22 12:32
    AC or DC?

    Leon

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  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2008-10-22 17:32
    If AC, what is the needed frequency response? Can the output be inverted?

    -Phil
  • computer guycomputer guy Posts: 1,113
    edited 2008-10-23 04:45
    DC.

    The input is a coil of copper wire that produces 600mv of power when a mobile phone is put close to it.

    I managed to get an op-amp, a 100k and 470R resistor and get it to boost it to 5v. When the phone is far away I get 5v when it is close I get about 4.2v

    It would be nice to go from 0v to 1.5v though.


    Thank you smile.gif

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  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2008-10-23 04:52
    A coil pickup without rectification and filtering is going to give you AC, not DC. You're on the right track with the op-amp, though. Can you show us a schematic for what you've done so far?

    -Phil
  • computer guycomputer guy Posts: 1,113
    edited 2008-10-23 05:14
    attachment.php?attachmentid=56340

    R2 = 100k
    R1 is 470R

    The coil goes between Vin and GND

    It is a RC455BPS op-amp.

    The power source for the op-amp is 12v.


    Thank you smile.gif

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  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2008-10-23 05:24
    computer guy,

    What are your coil dimensions? ...and what frequency are you able to detect?

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    Beau Schwabe

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  • computer guycomputer guy Posts: 1,113
    edited 2008-10-23 05:31
    The coil was quickly made from scrap insulated copper wire.
    The diameter of the space in the middle of the coil is 4-5mm.
    The coil when wound is about 10cm long.

    I know I could get better performance if I had it the right dimensions.

    The frequency reading from an oscilloscope is 6 to 8 KHz


    Thank you smile.gif

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    Building Blocks To The Propeller Chip A web site designed to help people who are new to the propeller chip.

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  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2008-10-23 06:10
    Ok, so roughly 7 turns on a 4.5mm coil form?
    What processor are you planning on using? (BS1,BS2,SX, Propeller)
    ...there is likely a solution available to you without using an Op-Amp.

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • computer guycomputer guy Posts: 1,113
    edited 2008-10-23 06:14
    The copper wire is about 0.2mm thick.

    A BS2. Im wanting to detect a phone signal.


    Thank you smile.gif

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    Guitar Hero controller using the prop (WIP) --> HERE
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2008-10-23 06:42
    computer guy,

    Let me think about this.... You basically want the I/O threshold of the BS2 (about 1.4V) to detect the 0.6V signal induced on the coil in proximity to a Phone correct?
    ...and possibly a way to also detect distance? ...as the coil is removed from the phone?

    The first part is pretty easy... raising or lowering the voltage threshold depending on how you look at it. But determining the distance can get tricky. Let me sleep on it,
    and I will try to have an answer sometime tomorrow.

    Am I right though on the wire? (about 7 turns)

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • computer guycomputer guy Posts: 1,113
    edited 2008-10-23 06:57
    I don't know much about coils but physically it is about 40 turns.
    Distance isn't really a problem. I simply want to put my phone in a cradle (with the coil built in) and have it on silent.
    When I get a call the BS2 will notify me (don't know how yet).


    Thank you smile.gif

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Building Blocks To The Propeller Chip A web site designed to help people who are new to the propeller chip.

    Guitar Hero controller using the prop (WIP) --> HERE
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2008-10-23 15:59
    computer guy,
    ·
    Here is a circuit that should work for you that does not use an Op-Amp.· Set the I/O pin to an INPUT and monitor the pin with a·DEBUG....
    ·
    'For example if your coil·is connected to P4
    TestLoop:
    DEBUG BIN IN4,CR
    GOTO TestLoop
    ·
    ...Adjust the POT right on the edge of the I/O threshold so that when the phone is not present (Coil is quiet) you either get all 1's or all 0's.
    ·
    If you adjusted for·all 0's, then when the phone is present you should see 1's inserted among the 0's.· Likewise, if you adjusted for all 1's, then when the phone is present you should see 0's inserted among the 1's.
    ·
    In your code, you would simply look for the opposite state present (trigger event) that you adjusted the POT for.· If you needed to measure the frequency, you could use the COUNT command after you have determined a trigger event had occurred with a simple IF/THEN.
    ·


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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
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  • computer guycomputer guy Posts: 1,113
    edited 2010-04-26 01:57
    Thanks Beau.

    Will try this out. smile.gif

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