Audio-activated Switch [Bluetooth Remote]

Discussion in 'The Projects Forum' started by ddm, Mar 4, 2011.

  1. ddm

    Thread Starter New Member

    Mar 4, 2011
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    Hello everyone, and thanks in advance if you are willing to help me out :)


    I do a lot of low-light photography, so I already made a handy cable release for my new camera. The problem is, there is still a physical connection between me and the camera through the cable, so a tiny bit of vibration still passes through, ruining the point of a cable release.
    I could pay Canon ~$30 for an infrared remote that will only work up to 5 meters, and will still not allow me to use Bulb mode properly.



    So, I devised a little plan. I have an older Bluetooth headset.
    I can take the mono audio output of it, and I need a simple switch to activate based on the signal.
    If I can accomplish this, I can write an application for my phone that would connect to the headset and send a simple signal to it (say, silence for "do nothing" and a 400hz tone for "open shutter"). This would not only give me radio-based remote control of the camera up to 10 meters (maybe more if I can mess with the headset's antenna?), it would also allow me to programmatically control it, and turn my phone into an expensive intervalometer.


    TL;DR:
    I need a simple circuit that will take an audio signal, and when a specific amplitude is reached (or a specific frequency - this would be the better, but probably harder option), would create a short circuit across the camera's shutter release, making it expose.

    I thought I could get away with a simple transistor solution, but as far as my limited knowledge goes, transistors are pretty much useless for this purpose once the signal level goes below 0.6 V. This is just an in-ear headset, and I'm almost certain the signal will never go that high.




    The optimal solution would only detect a specific frequency (bandpass filter + amplification + a transistor?), eliminating false positives (say if I get a call on the phone and the headset starts beeping), and this would also allow me to build a second copy of the circuit tuned to a different frequency, controlling the auto-focus too.



    If this (seemingly) simple problem can be solved, I could create something that is far more advanced than anything the camera's manufacturer, or indeed any third party, has available. Obviously a dedicated RF transmitter+receiver would work better as a remote, but I already have a microcomputer in my pocket, and this would put it to some very good use! :)



    Sorry if I blabbered on for too long, and thanks again in advance if you'd be so kind and help a n00b out. :p
     
  2. ddm

    Thread Starter New Member

    Mar 4, 2011
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    Anyone? :( I thought this would be simple to do.
     
  3. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Did you actually put TR;DR in there?
     
  4. ddm

    Thread Starter New Member

    Mar 4, 2011
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    Yes I did :) I didn't want to bore anyone who doesn't want to read the whole point of the project given that the actual question is pretty simple.


    I've been reading through the e-book on this site, and it's extremely helpful! Whoever wrote it and published it for free is an awesome person. :D

    At the moment I'm thinking: I need to add some DC bias voltage to the signal (perhaps just wire a button cell in series with it) to raise it above 0.6v. But the amount of fluctuation in the signal would still be very small, so I'm still missing some crucial element. Anyone got any ideas?
     
  5. blueroomelectronics

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    Jul 22, 2007
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    What model is the camera?
     
  6. ddm

    Thread Starter New Member

    Mar 4, 2011
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    Well... that doesn't really matter much, pretty much all camera manufacturers have the same system for cable releases (even if the connector is different): short one contact to ground to make the camera focus, short the other to ground to make it expose.

    But to answer your question, it's a Canon EOS 500D. :)
     
  7. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    On some Canons you can make a long USB shutter cable. Custom firmware might also offer some solutions to a remote shutter or even time lapse.
    http://chdk.wikia.com/wiki/CHDK
     
  8. ddm

    Thread Starter New Member

    Mar 4, 2011
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    Yes, I know. I love CHDK. I used it all the time with my old Powershot, I used to write scripts for it and all. :) But CHDK doesn't work on DSLRs.

    And the USB thing... it doesn't really matter whether I'm using the USB port (like you would with CHDK) or a dedicated shutter release port, I'd still need this circuit in both cases. Or better yet, a complete RF receiver and transmitter, but that is a little bit over my head at the moment.

    The whole point of this project is that I need it to be wireless, and I need it to have longer range than any 'official' solution allows.

    But if I can make a circuit that activates based on an audio signal, then I've already got the receiver and transmitter all designed for me, and gaining the ability for programmatic control.
     
  9. blueroomelectronics

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    Jul 22, 2007
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    What sort of range do you need?
     
  10. ddm

    Thread Starter New Member

    Mar 4, 2011
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    The more the better. The primary point of it is just to remove all physical connection between me and the camera, but I would occasionally need to be further away from it (like when doing light painting or self-portraits). 5 meters is definitely not enough given the sort of structures and locations I will be photographing in. 10 meters (the range given by Bluetooth) would be more or less enough in most situations, but gaining programmatic control would make it completely worth it. (I can just write a program that waits for 2 minutes and then leave my phone near the camera for example)
     
  11. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Since you can program, you might want to consider a pair of XBee radios. They have the same range as Bluetooth and the Pro version can be several kilometers. A small pair of reed relays on a couple of I/O pins would work your camera. These radio modules are small and about $20 each.
     
  12. ddm

    Thread Starter New Member

    Mar 4, 2011
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    Thanks for the suggestion, those really do look handy for a more complex project I'm also designing.

    But seriously, is it really that difficult to detect a certain pitch (or even just a rise in amplitude) in a low-level audio signal? That XBee radio is way overkill for something as simple as basically passing a single bit through.


    Edit: also, relays (anything that creates mechanical motion of any degree) would completely ruin the point of the entire thing. But there's no need for any significant amount of current to be passed at all, so I'm sure a transistor would do just fine to do the final switching.
     
  13. blueroomelectronics

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    Jul 22, 2007
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    Google 315MHz or 433MHz RF modules.
     
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