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Circuit Wanted To Buy...

Discussion in 'General Electronics Discussion' started by blktoptrvl, May 21, 2011.

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  1. blktoptrvl

    blktoptrvl

    1
    0
    May 21, 2011
    Hello all.

    I am not an electronics guy, nor do I wish to become one - meaning that I do not wish to learn electronics. I am just here to see if there is anyone who might be interested in designing and building a circuit and selling the result to me.

    I am assuming it is a relatively simple circuit from what I have been able to read (but hey - what do I know), but I do not have the time to learn, design or build it. If anyone here can, and is interested, I would be happy to pay for the completed product.

    The following is a description of what I need.

    Wanted To Buy...

    An Electronic device (and documentation thereof) with a circuit that will (at base state) pass 9 volts as long as the circuit is sensing vibrations. When the vibrations stop, the circuit will continue to pass 9 volts for x more minutes. However, if before the x minutes are expired, there is a new vibration sensed, the circuit will go back to the base state.

    [In this writeup, x is variable between 5 and 30 minutes.]

    The next time the motion is stopped, the timer will again begin at x minutes.

    This device should be sensitive enough that the vibrations associated with walking down the street will keep the voltage flowing.

    The device should use 16 guage wires to pass power and must fit within a 2.5" x 2.5" x .5" plastic box.

    Once the time (x) expires, the circuit should draw 0 volts and will not draw any voltage again until a new vibration is sensed.

    I will pay for the documentation of the circuit and the prototype as a matched set.


    If anyone is interested in building this, please drop me a private message with a price.

    Thanks.

    BTW, if this message is outside of the tradition or protocol of this site, I mean no offense.
     
    Last edited: May 21, 2011
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,473
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    Jan 21, 2010
    OK, firstly, it is unlikely that you will find someone willing to do this (but nothing is impossible).

    However, you need to describe the device in terms that people will understand.

    For example, you might have stated:

    A want a device that will power my MP3 player while I am walking, but turn it off after 5 to 30 minutes (set by a control) if I stop walking. I believe that walking could be detected by sensing vibrations. The device needs to fit in a box 75mm x 75mm x 12mm.

    I have no idea if that is what you want or not.
     
  3. poor mystic

    poor mystic

    1,068
    31
    Apr 8, 2011
    I agree with Steve... :-D:-D:-D
    Although electronics is cheap in bulk, that's purely because of mass production. Nobody can afford to give you this sort of thing for the same price as it would be if you'd found what you want all ready to go in a retail shop. There's too much work in it!
    Electronics design is a high-stress activity which uses all a person's brains. Good electronics is designed by clever people who think so hard for so long that they find simplicities where you just wouldn't expect them. Such people have trained for years. It's hard work. What is their time worth? Hard to say, I know my workspace cost my company $300/hour 25 years ago... what does it cost now even to set someone up with everything they need for technical work? I had at least $50,000 worth of gear at my disposal, back then. That's what a bespoke designer would need.
    So! Are you a billionaire with a nice attitude? I can do such work for you if we become friends, part-time only (else I won't stay fresh and creative), for a good salary.
    You will need real wherewithal to get what you want!
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,473
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    Jan 21, 2010
    Presuming that what I stated is what the original poster requires, it neatly illustrates the 80/20 rule that applies to the design of something like this.

    For example, the basic design might be some sort of vibration detection, a PIC and a MOSFET to pass the current.

    Then we need to consider how it might work, and what quiescent current draw is acceptable. The requirement that it draws no power (not voltage btw) is not achievable, but you can get pretty low. An average of 20uA to 50uA should be achievable.

    The current it needs to pass is not stated, but let's assume it's low enough that a single MOSFET can do it easily (say less than a couple of amps).

    The vibration sensor is the first problem. We need to determine what's available, and how much vibration walking generates. What if the person has the device in something spongy (say a handbag) and is walking on a soft surface? And remember that it has to operate at a very low current if the device requires power.

    The software for the PIC is pretty simple. But do we need to allow for the odd vibration when the device is off? if it's too sensitive then people walking past a table with the device on it may be picked up as "walking".

    Then we need to consider what power connectors are required.

    Then we need to build one up to see how it performs. Debugging etc follow, finally (perhaps) it needs to be housed in something.

    Then there's the documentation. Lets assume what is required is:

    1) schematic
    2) PCB layout
    3) Discussion of theory of operation
    4) Parts list
    5) Service info
    6) PCB design stuff to allow for mass production(?)
    7) Software source
    8) software documentation
    9) compiled firmware
    10) Documentation of development environment
    11) programming info
    12) user manual

    And probably more. Or maybe less. It may take quite some time to determine exactly what you require, document it, and create a contract.

    I guess that those of us who do some of this on a daily basis would prefer not to do it in our spare time as well :)
     
  5. shiekh

    shiekh

    77
    1
    Oct 11, 2010
    Just for fun, just how easy could this be done?

    A tiny speaker with a weight attached to the cone could be used to detect vibration, the signal could be fed to a transistor that fills a capacitor that runs an op-amp to switch the main 9V. Without filling the capacitor runs down in time ~RC

    Even so, developing such a project would cost big bucks as has been noted here.
     
  6. poor mystic

    poor mystic

    1,068
    31
    Apr 8, 2011
    Not bad, Shiek! Not bad at all!
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,473
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    Jan 21, 2010
    Shiek's idea is good, but suffers from 2 problems:

    1) it consumes power when waiting for vibrations (Hard to get around, but see the stated requirements)
    2) it is sensitive along 1 axis only.

    The second point can be rectified by having more than 1 sensor, or by ensuring that the major vibration to be detected is along this axis.

    The first point is harder.

    One method would be to have a traditional mechanical vibration detector (or several for multiple axies) When these make contact they could apply a voltage tot he gate of a mosfet which turns on and resets a timing circuit. This timing circuit also holds the mosfet turned on until the timer times out. It switches off the mosfet and removes power from itself at the same time. The vibration detector would also reset the timer so that the timeout would be from the last vibration, not the first.
     
  8. shiekh

    shiekh

    77
    1
    Oct 11, 2010
    True, my proposal was not well thought out, and far, far from perfect.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,473
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    Jan 21, 2010
    But it is definitely a method of producing a sensitive vibration detector. Absolutely nothing wrong with that.

    I'm sure you could probably come up with an amplifier having a very low quiescent power requirement. You're not limited by the amplifier having to exhibit lack of distortion or wide bandwidth, so you can do things you would not in an audio amplifier.
     
  10. poor mystic

    poor mystic

    1,068
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    Apr 8, 2011
    ... like for example the generating coil might be grounded on 1 side and feed the base of a high-gain darlington pair with the other. Half-pulses would charge a 100 microfarad capacitor in the collector with 10 Megohms in series. A separate RC network would smooth Vc with respect to ground, out to the right on the drawing. The averaged Vc would be measured against a 10 meg potentiometer by a low-power comparator, whose output would pull down to switch a P-channel Mosfet in the positive rail.
    If the speaker were too low power we could use the spring out of a ball-point pen, with a little rare earth magnet and a good wrapping of litz wire.
    ... right about now, we're off to see the customer for development costs, with progress payments to be made at defined stages of the project.
    How many did you say you wanted?
     
  11. poor mystic

    poor mystic

    1,068
    31
    Apr 8, 2011
    I see it still needs lots of attention.
     
  12. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    A ceramic record player stereo pick-up would do two axes, it would have a relatively high voltage suitable for matching to a fet. A weight would need to be added instead of the needle.
     
  13. john monks

    john monks

    693
    1
    Mar 9, 2012
    You might consider using a self charging magnetic flashlight modified so that internal capacitor drives a DMOSFET gate on. A 9 volt battery can be installed in series with the FET and the remaining leads would be your output. Maybe a TN0604N3 would work. The circuit draw should be less than a few microamps. Self powered motion detectors are hard to come by but that's what you need to drive the FET.
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    You could check out a pedometer. They often run for (almost) ever on (again, almost) no battery at all. How do they do it?
     
  15. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Newbie here, just came across this thread...

    I know it's old, and as others have said custom electronic design is not cheap but there are people like me that will work at a reasonable rate to design custom circuits when I have time or when the project interest me...

    As far as this circuit goes, it's not complicated at all in fact it's pretty straight forward and simple to build, if the original poster is still around and ready to give more input I might be interested in working out a deal...

    One, thing I will comment upon is the fact that the build requirement requires no draw when idle, with todays low power sleep modes on µ-chips this is really impractical for most designs... The low power sleep modes generally draw less or equivalent to the normal idle discharge of a battery just sitting there alone, thus from a cost perspective it's simply easier and more cost effective design wise to put a chip to sleep vs designing and implementing a zero current drain wake up circuit... The current draw when active will be hugely and exponentially more than when just sitting idle and will really be the limiting factor on battery life, in sleep mode with a few AA or AAA batteries you can easily expect 6 months of idle sitting around without killing a battery, theoretically you could get years of standby.

    The other big factor in this as has been touched upon is the sensitivity of the design, its dead simple to make a mechanical motion sensor but will that suit this build, or is it going to require some high end solid state device with fine tuning ability? You can build a dead simple motion detector by soldering a BB or small ball bearing onto the end of a small spring or piano wire, and inserting that into a conductive metal tube... The ball bearing on the end of the spring is held centered in the tube by the spring or wire,when jarred it makes contact with the side of the tube completing a circuit, presto motion sensed... The diameter of the tube and/or the stiffness of the spring will determine the sensitivity, by trial and error mostly. Place two or three of these at different axises and you will have a very basic but reliable multi-direction mechanical motion sensor...

    You can pick one up at the dollar store and tear it apart, they generally have a small ball bearing in there there rolls inside a tube, upon contact with each end in completes a count circuit, it's only on and drawing power when the ball bearing is moving, and as stated above the sleep drain with modern µ-chips is insignificant overall. Heck the sensor out of one of them could be used in this project in the most basic form...
     
    Last edited: Apr 7, 2012
    Wakoli Chokeli likes this.
  16. Django Fawkes

    Django Fawkes

    10
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    May 16, 2012
    I don't know much about "raw" electronics, but that kind of sounds like it could be done with an Arduino board. Arduino is really easy to use if you're shown how from a good source and should fit in to the size if you were to build your own board. I think the alternative of having a custom built circuit would be more complicated.

    Seeing as you can already speak in variables, I think you should give arduino a shot.
     
  17. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Overkill, the main concern is the development/choice of the sensor (sensing circuit) itself not the micro handling the logic, a 75¢ micro can handle the logic required for this project, no need for a Ardunio developer board...

    The obstacle is designing and developing the actual sensor circuit and that is mostly independent of the micro or logic chips that will take the sensor data and do the appropriate things...
     
  18. Raul

    Raul

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    Sep 25, 2012
  19. Wakoli Chokeli

    Wakoli Chokeli

    6
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    Nov 16, 2016
    Will be interested to design and guide till the end. Just thinking about 2.5" x 2.5" x .5" plastic box though. If anybody wants to join me as I design, you are welcome. Let me know if you need videos of the built process in advance. Please don't ask the cost, am considering it my project as well.
     
    Last edited by a moderator: Nov 16, 2016
  20. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    The original poster never came back. And is been 4 years.
     
    HellasTechn likes this.
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