Recycling an old fm radio into phone's speakers

Discussion in 'The Projects Forum' started by or756, Jun 14, 2013.

  1. or756

    Thread Starter New Member

    Jun 14, 2013
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    Hey.

    I found an old little fm radio in my house while cleaning my room.
    This radio is working fine, but I have no use for it so I thought to myself why to throw it away ?

    It has a 3.5mm output so I thought I could turn it into an intput.

    I know its possible, but I lack the required knowledge.

    That's where I need you :)

    By the way the power source is 2x AA batteries, and the yellow "free wire" doesn't connect anywhere, the radio is still working perfectly

    Some pics :

    A picture of the parts :
    [​IMG]



    Pic of Circuit board (the big black box at the bottom left side of the pic is the 3.5mm output)

    [​IMG]


    The other side of the circuit board , the 3.5mm output is at the top left side, and the silver wheel at the top is the volume controller

    [​IMG]


    I you can help me.

    Thanks in advance ! :)
     
  2. wayneh

    Expert

    Sep 9, 2010
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    If you lack the knowledge, how do you "know" that an audio output can be converted into an input? It cannot.

    Are you hoping to turn this into a mr. microphone type transmitter?
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    If you connect your input signal across the volume control wires, that's the two on the outside possibly green and red , the wiper blue connects to the amplifier.
     
  4. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Gee that amp is crude!

    It's only mono, and uses just 3 transistors. Looks like 1 tran as a common emitter driver and a 2-tran push pull output stage.
     
  5. or756

    Thread Starter New Member

    Jun 14, 2013
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    No, I want to connect my iPod to it and make it a speaker, like the ones you buy for 5$ at eBay

    I'm afraid I did not understand you ... lol

    Same here.

    So... Is it impossible? because at first sight it looks possible indeed..
     
  6. Ramussons

    Active Member

    May 3, 2013
    557
    92
    If you really want to:

    It can be done.
    It will not be stereo.
    You will have to cut tracks on the pcb, rewire some.

    Can we have a photo of the volume control connection (which colour wire to which terminal) and the pcb side of these wires and the jack mounting?

    Ramesh
     
  7. or756

    Thread Starter New Member

    Jun 14, 2013
    4
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    Sure !

    Volume control pic :

    [​IMG]

    *The black wire connects to the batteries

    Pcb pics : (if you can't see the pcb pic, its on the first post )

    [​IMG]


    Jack pics :

    [​IMG]

    [​IMG]
     
  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Looking at the bottom of the PCB, the signal out from the FM IC goes to the blue wire to the pot.

    The red wire from the pot is the audio signal out of the pot, it goes through a ceramic cap and a resistor (C9 and R9), and connects to the middle pin of Q1 which is the base of the Q1 preamp.

    So if you remove the red wire from the pot PCB you can inject an audio signal there, or you can remove the blue wire from the large PCB and inject the audio there which will keep the pot in circuit and working.
     
  9. or756

    Thread Starter New Member

    Jun 14, 2013
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    Thank you for your comment!

    So what I need to do is remove the blue wire from the PCB and connect it to the 3.5mm Jack ??
     
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Yep. And the jack ground needs to be the radio ground.
     
  11. Ramussons

    Active Member

    May 3, 2013
    557
    92
    No, not that simple. The jack is connected to the amp output; first you need to isolate it.

    Anyone know how to "draw" on the enclosed photos? :mad:

    (editing a hard copy of the photos for scan and upload . . . . )

    Ramesh
     
  12. Ramussons

    Active Member

    May 3, 2013
    557
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    Ok, I can do that in windows Paint !

    Ramesh
     
  13. wayneh

    Expert

    Sep 9, 2010
    12,094
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    Just about any drawing or painting application will allow you to import an image and then draw over it or paint directly in the image. I prefer drawing to painting, primarily because the original image is not touched, but to each his own.
     
  14. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Just two minutes to resize (Windows), write and draw (Paint).

    I do that with pictures to be inserted in my reports when I need to add something to them.
     
    Last edited: Jun 17, 2013
  15. Ramussons

    Active Member

    May 3, 2013
    557
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    Yes, I found that out. Thanks for the hints all the same.

    Ok, or756, here we go.

    I have attached a photo about the changes to be made.

    There are 2 steps.

    The First step instructions have been written on the photo. That's breaking the Track, Cutting the yellow Speaker wire and Re routing it. You also disconnect One end of a Resistor (56 Ω ?).

    (Frankly, I could not make much sense of the schematic :eek: )

    The Radio should operate normally at this stage, except that the jack has been isolated and bypassed.

    The second step is to combine the input from the jack (2 numbers of 100 Ω Resistors) connected as shown. The Blue wire from the Volume Control is disconnected from the PCB and routed to the common point of the 100 Ω resistors.

    A feed back will be welcome.

    Ramesh
     
  16. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    That was my fault sorry, I assumed there would be a new jack for the incoming sound signal.

    The existing jack can be used for a decent sized external speaker, which will improve the sound and volume a lot.
     
  17. Ramussons

    Active Member

    May 3, 2013
    557
    92
    True, and that's what I would do. All it requires is an additional socket, a couple of resistors.

    Ramesh
     
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