Voltage Amplifier

Discussion in 'The Projects Forum' started by pradeep76, Nov 5, 2012.

  1. pradeep76

    Thread Starter New Member

    Nov 5, 2012
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    Hello
    I want to know how much voltage is in a phone ear piece when someone send a text message to the phone and what is the best way to amplify or multiply it for other reasons.

    Regards
    Pradeep
     
  2. wayneh

    Expert

    Sep 9, 2010
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    The voltage will depend on the specifics of the phone - they will not all be the same. That said, the voltage is likely in the 1-10V range.

    Can you access the connections to the ear piece? If so, almost any audio power amplifier would amplify the signal. If you cannot access the signal directly, you can have another microphone "listen" to the phone and again use an audio amp (probably with a pre-amp first) to amplify the signal from that microphone.

    If your "other reasons" include something other than making the signal louder, you'll need to elaborate on your plans.
     
  3. pradeep76

    Thread Starter New Member

    Nov 5, 2012
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    Thanks for the reply. I have Motorola Atrix where I have install an app for video streaming. What I am trying to build is a garage doors opener/ closer. My plan is use skype to send a message to phone and use the message tone to build enough voltage to close garage door.

    Is this possible. I was looking at you tube and there something like this made using Bluetooth. But I don't like the pairing /unpairing part.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    Closing the door won't require a "voltage", it likely requires closing a contact like you do when you manually hit the button on the wall. So you need a way to activate a relay or such when the phone receives a text. It's possible. To avoid altering the phone at all, I recommend a circuit to "listen" for a tone. If you can use a specific ring tone, that would help because the circuit could filter out other noise and prevent that noise from opening the door unexpectedly.

    You plan on leaving a dedicated phone "on" so that you can control your garage door? I don't understand why you wouldn't just use a garage door remote like everyone else. What's to keep a random spam text from opening or closing your door?
     
  5. pradeep76

    Thread Starter New Member

    Nov 5, 2012
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    This phone does not function properly. Touch screen is bad etc.
    What remote controls are available out there. Can you share couple links. I was looking at some but they are expensive.

    I am planning to use a dedicated account for text messaging where me and my wife only can send message to it.

    Like I said there is a bluetooth version available http://www.youtube.com/watch?v=6cAtso2tzMo

    I guess final goal is to learn and build something cheap. Let me know if you have any other ideas to make it happen.
     
  6. wayneh

    Expert

    Sep 9, 2010
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    I'm not sure there is such a thing. Your carrier might send you a message or you might get a wrong number. I occasionally receive spam texts on my phone. Maybe your carrier can allow you can block all but certain numbers. Still, have you ever butt-dialed someone? I'd hate for my garage to open as a result!

    Here's an example of a garage door remote. This would be cheaper in the long run than a dedicated texting account.
     
  7. pradeep76

    Thread Starter New Member

    Nov 5, 2012
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    I totally understand your concern. But my plan is to use a dedicated skype account which I allow who can send a message to. I have these local remotes. But I want one which I can use from physical remote/out a site location. This phone does not have service, it is on WiFi.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    Ah, OK, that makes a lot more sense.

    Question: Do you think you can get at the internal speaker, or vibrator motor if it has one? If you can do so easily, then you won't need a microphone to "listen" to the phone and the rest of the circuit can be a bit simpler.

    If you'd rather not risk opening the the phone, you need a microphone. Old cordless phones are a good place to find one free. I'd place it directly on the phone with a drop of hot glue.

    The next step is to detect the tone. Maybe someone can jump in here with a good tone detector circuit. I think it's usually an op-amp as an integrator? I'm not sure it will need a frequency filter to avoid triggering on thunder claps, car honks, barking dogs, fire alarms and such.

    The next step is to compare the output of the tone detector to a variable reference voltage. Once the voltage surpasses the setpoint, due to "tone on" detected, the comparator output can be used to trigger the door. The reference voltage is set to be sensitive enough without false triggering.

    Depending on the door motor circuit, you may need a transistor and/or a relay in between the comparator and the door circuit. To decide, you need to know what power is in the existing door switch. 24V AC is common, but it could be DC and it could be a different voltage. If it's AC, you'll want a small relay to act as the switch. If it's DC, the comparator alone might do it or you may need a transistor for more current. (The comparator cannot sink more than about 5mA.)

    If the switch voltage is DC and you have a multimeter, use its ammeter mode and put it in series with the door switch to see how much current is drawn when you press the button.

    Finally, I haven't read this but it might interest you.
     
  9. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    My question is, why would you want to open your garage with a cell phone?

    If the phone is on wifi then there are much better ways of doing this.

    Here is one of many.

    http://atmega32-avr.com/wifi-microcontroller/
     
  10. wayneh

    Expert

    Sep 9, 2010
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    "Many" is right. Hacking garage doors seems to be a popular pastime.
     
  11. alliknight

    New Member

    Dec 7, 2012
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  12. MrChips

    Moderator

    Oct 2, 2009
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    Easy. Phone your wife and ask her to open the garage door.
     
    absf likes this.
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