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Changing the speed of a walkman motor with motion

Discussion in 'Sensors and Actuators' started by foundry, Aug 4, 2013.

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  1. foundry

    foundry

    11
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    Aug 4, 2013
    Hi there,

    I'm new here. I'm not very experienced working in electronics, although i love to experiment. I was hoping someone may be able to shed some light on a problem i'm having.

    I'm currently working on an interactive art installation.

    My idea is to alter a series of old walkman cassette players so that as people move around them, the speed of the motor changes.

    I know that when walkman batteries become weak, the tape gradually slows down. This is the effect i would like, but so far i've only been able to shut the motor down entirely.

    Essentially i would like it so that when someone is close to the walkman/sensor, or walks past it, the speed slows down, and when they move away it returns to normal.

    I thought that using a motion sensitive switch (or potentiometer?) of some kind may work, but i'm really lost as to what components might be available for this, and whether this is in fact possible.

    I did already try an LDR, but i couldn't get it to work.

    The walkman runs off two AA batteries.

    It seems like a simple idea, but perhaps it's something that's actually quite complex to achieve. Either way, any light anyone could shed on this would be a real help to me.

    Thank you!
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Detecting people is most easily done using PIR sensors. There are some PIR modules available quite cheaply that could be used to trigger a mosfet which shorted out a resistor in series with the batteries or something similar.

    You would need to determine if a simple resistor in series with the batteries gives you the change in speed that you desire.

    The way I have described it, the motors would run slow until someone walked in front of the sensor. Then they'd go back up to speed.

    You'd probably want to run the walkmen (is that the plural of walkman?) from an external power supply so you don't have to mortgage your house to buy batteries all the time.
     
  3. mikgol

    mikgol

    87
    1
    Jul 6, 2013
    You could do it with software running on a PC, and use a USB experiment board to control the motor speed with PWM. You could then use a Kinect to sense people and how close they are.
     
  4. Lord_grezington

    Lord_grezington

    124
    2
    May 3, 2013
    I think the best option is to go for an ultrasonic proximity sensor (similar to what is used on a car parking sensor) a PIR will only give you an either on or off (digital signal) where as a proximity sensor will allow you to vary the motor speed depending on the distance the person is from the sensor.

    The issue is they don't come cheap if you want something that is not the standard parking sensor. I take it you want to measure over a couple of meters rather than a few centimetres? These things work off a frequency of pulses, ie the closer they are the higher the frequency. so you will need some sort of signal processing to analyse the pulses and then control the motor drive electronics.

    I have not used the parking sensors before, but if I were you as these are going fairly cheap, get some in and do some testing on them. These will be your best option if you want to sense over a meter or so.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Here is a cheap ultrasonic module.

    They are triggered by an edge on one pin and emit a pulse with length proportional to the distance to the closest object they "see"

    Whilst usually used with a microcontroller, you could also use some fairly simple logic to detect certain fixed distances.
     
  6. foundry

    foundry

    11
    0
    Aug 4, 2013
    Hello again everybody,

    Thanks so much for your responses. I'm sorry i didn't get back sooner, i had to rush off to Europe for a few days and my laptop managed to die on me.

    I've managed to find out how to alter the pitch of the motor. Reading this article gave me some insight into the process: http://ofsoundmind.wordpress.com/2008/01/24/primer-pitch-bending-a-walkman/

    The Walkmen models that i have purchased and am hoping to modify are: Sony WM-FX443 and WM-FX423

    I've managed to find a couple of service manuals, i'm not able to decipher them myself, but someone informed me that it would be possible, as in the article, to replace the potentiometer.

    With that in mind, will it then be possible to control this pitch adjustment with the ultrasonic sensors you guys mentioned?

    (*steve*) - i'm actually based in the UK, but i've managed to find the modules you mentioned fairly cheap here. If they would be suitable, what other equipment would i need to help them operate with the Walkmen?

    Thanks again for all the help,

    James
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I recommend you see if the devices you have include the speed adjustment as per that article.

    If they do, it *may* be possible to adjust the speed with something that replaces that pot.

    I would be looking at a microcontroller, an ultrasonic rangefinder, maybe a digital pot, and quite a bit of software.

    It would be a bit of work and require some probably quite new skills for you...

    A lot also depends on how that speed control works...

    You could perhaps also use a servo to control a pot directly, but that might wear out the pot pretty quickly (it would certainly wear out the trimpot)
     
  8. foundry

    foundry

    11
    0
    Aug 4, 2013
    Thanks a lot for your response Steve.

    From what you mention, it does sound quite complex for my skillset!

    Fundamentally, all i want to do is have the sound change based on some kind of proximity interaction...it would be great if this was gradual, as opposed to on off...other than that it doesn't matter so much. The idea of the piece is largely to explore interaction.

    I would love to do what you've described, but if it's too much for me to realistically achieve then i'm happy to consider any and all ideas.

    Thanks again, really appreciate your advice on this
     
  9. foundry

    foundry

    11
    0
    Aug 4, 2013
    Hi again,

    Today i had some success with the Walkmen. I was able to dissasemble 2 that i have and locate the potentiometers in each case that control the speed.

    I have decided that in the first instance i would like to try swapping these potentiometers out for light dependent resistors. It's possible that this approach may serve me well if i can adjust the environment correctly.

    I am having a little trouble however understanding how light dependent resistors relate to potentiometers, and as such how i can select the correct ones.

    For example, one of the pots is apparently 4.7k; in this instance which LDR would be best to replace it?
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    We would have to see how the pots are connected. It may be possible to place an LDR in their place, or it may require another resistor, or.. it may not be possible.

    Take a photo of both sides of the board on which the trimpot is connected.

    We need nice clear, sharp photos so that we can read the markings on the components. Take the photo in indirect light (outdoors in shade is perfect. DO NOT use flash.)
     
  11. foundry

    foundry

    11
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    Aug 4, 2013
    Thanks a lot (*steve*), really appreciate that. I will get on the case straight away. I have a reasonably good camera so should be possible to get some accurate shots i hope.
     
  12. foundry

    foundry

    11
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    Aug 4, 2013
    Hi Steve,

    My camera wasn't so effective at very close range, so i scanned the boards instead. I got quite clear results on one of them (the FX443), but not so much on the FX423.

    I can try re-shooting if it's still not possible to view the necessary details, however i have also included the schematics from the respective service manuals, so hopefully these will help.

    I've also tried to point to where it seems the speed control pots are on the board photos, but i'm definitely a novice so i may be wrong on this.

    Some information that i have received about the two models (which may help, although again i'm no expert so can't say if it's accurate) is that:

    The FX423 uses a DC motor. The speed control adjustment is a 470Ω pot in series with a 560Ω fixed resistor.

    The FX443 uses a three-phase stepper motor. The speed control adjustment is a 4.7kΩ pot with 4.7kΩ and 5.6kΩ resistors to form a variable voltage reference.


    Massive thanks once again for your help Steve.

    Here are the images (if you need to see them at very, very large size it's possible to do so by clicking the images through to Photobucket where they can be magnified to full size):

    SONY WM-FX423

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    SONY WM-FX443

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
  13. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
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    Nov 28, 2011
    I grabbed the service manual for the WM-FX423 from elektrotanya.com. Here is the relevant part of the circuit.

    [​IMG]

    That site also has the WM-FX443 but the site has a daily download limit. I'll get it tomorrow and upload the schematic in a separate post.
     

    Attached Files:

  14. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Attached Files:

  15. foundry

    foundry

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    Aug 4, 2013
    KrisBlueNZ - thanks so much for these, really kind of you to do that.

    From looking at these, does it seem possible that the circuit will work, and the speed of the motor can be controlled with an equivalent light dependent resistor?
     
  16. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Here's the info for the other walkman - the WM-FX443.

    [​IMG]

    [​IMG]

    [​IMG]
     

    Attached Files:

  17. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,374
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    This one uses the pot as a simple variable resistor. It appears to be a 470 ohm resistor and CdS cells have a minimum resistance which is not much lower than this, and a maximum resistance in the order of megohms (far, far higher).

    You might try wiring one in parallel with the trimpot. This would probably result in the tape player running fast when light reaches the cell, and slower (back to normal) as someone's shadow passes over it.

    The second one uses a higher value pot as a voltage divider.

    You could place a CdS cell between the wiper and one end or the other of the pot. This would most likely have a more dramatic effect and, depending on which side you place it, a shadow falling on the cell would speed up or slow down the tape.

    In either case, you're going to have to experiment and see what effects you get.
     
  18. foundry

    foundry

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    Aug 4, 2013
    Great stuff Steve, thanks a lot for this. I'm going to head out into town now to get a selection of CdS cells, but i notice there are many different types. Is there a specific type that you would recommend i get? Or should i try a selection?

    The place i'm going to is here: http://uk.rs-online.com/web/c/?sra=oss&r=t&searchTerm=ldr&x=0&y=0

    Thanks again, appreciate your help a great deal.
     
  19. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Both of those circuits are fairly low-resistance, so you should go for the LDR that has the lowest resistance values, otherwise the LDR will have no detectable effect unless it's very brightly illuminated. I suspect this will be a problem no matter which LDR you get, but it's still worth a try.

    Unfortunately, that selection table only has figures for one of the LDRs they offer. You may be able to find data sheets for the other ones though. Choose the one with the lowest resistance specification, but make sure that the illumination values are the same for the different types, otherwise you're not comparing apples with apples.
     
  20. foundry

    foundry

    11
    0
    Aug 4, 2013
    Thanks a lot for your help there KrisBlueNZ.

    I've picked up one LDR, and i will get another lower resistance one tomorrow too, so i will begin to do a little experimenting then, and we can see what happens...i do have an idea about the light and how to control it, but need to see if i can effect any change at all first...
     
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