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  1. #1
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    Default "Saw dust bin full" Sensor

    I've been toying with this idea for some time and after an 8 week period of stuffing around to get the right sensor I am finally able to make some progress.

    I posted about this is earlier today in the "Developments in Dust Sensor tech" but though I would start its own thread as I guess not many folks are that interested in the technical nature of the other thread.

    I got the prototype and software working on the bench last night.
    Its basically a weight or force sensor that is placed under the bin to measure the weight of sawdust and to sound an alarm when a preset weight is reached.
    This means it won't work on fully suspended collection bags but bins that are primarily resting on the floor or ground.
    If the bag is resting on the base of the DC frame a hinged secondary base could be added and this sensor could be placed under the side opposite the hinge.

    The force sensor is that gold foil rectangle which is an up to 50kg rated thin film variable resistor.
    The resistance ranges from >500kΩ near zero to around 70kΩ at 50 kg.
    Placed in a voltage divider the output V can easily vary enough to be picked up by a microcontroller.

    Developments in Dust Sensor tech-img_2417-jpg

    The resistance of the force sensor is inverse exponential and I calibrated it on a set of bathroom scales using lead weights.

    The force sensor will be embedded into a thin rubber pad and placed under the front bottom edge of wheelie bin collector at the mens shed.
    The wheelie bin wheels should take about half the weight and the front edge of the bin should take the other half.
    The sensor will be connected to the micro controller/display back inside the shed where the % fill of the bin is displayed on an LED display.
    Switch "Sw" can be switched to display the required alarm level using pot "P" .
    Then Sw is set back to display.
    When %fill of bin exceeds the alarm level the alarm (A) will sound.
    Of course a bigger alarm on a relay will be used in practice.

    Developments in Dust Sensor tech-img_2416-jpg

    A secondary calibration will be needed with the sensor under the bin font edge and will take place with the bin near full
    Trim pot "T" is part of the voltage divider and is part of the secondary calibration system.

    The microcontroller is a $4 Arduino Uno clone.
    The LED display costs $4
    The Sensor costs $11
    Total cost of parts is ~$25, excluding the alarm - given how deaf the men's shed members are it will need to be LOUD.

    As usual the much of the real work is in the turning the prototype into a robust actual product.
    Sorry am not making these for sale but the details and micro controller software will be freely available to anyone that wants it.

    Now I have to assemble it into an actual unit.

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  3. #2
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    I have done a bit more on the sensor.

    This is the "sensor foot" as I'm calling it.
    It's the bit that is under the bin and connected to the micro controller / display and alarm inside the shed.

    The foot is a pice of 3mm black anodised Al plate to which the sensor and junction box is attached.

    IMG_2418p.jpg

    A piece of 3mm thick Viton Rubber sheet is then siliconed over the sensor.
    IMG_2419p.jpg

    Here's a mock up of how the foot is place.
    I'm just testing it with that short piece of red flex but eventually I will need to use a much longer piece of flex.
    IMG_2421p.jpg
    IMG_2420p.jpg

    I picked up a 12V alarm from Altronics for $5
    Its 105dB at 3m and I will modulate it so it will be noticeable.

  4. #3
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    Quote Originally Posted by BobL View Post
    The microcontroller is a $4 Arduino Uno clone.
    The LED display costs $4
    The Sensor costs $11
    Total cost of parts is ~$25, excluding the alarm - given how deaf the men's shed members are it will need to be LOUD.

    As usual the much of the real work is in the turning the prototype into a robust actual product.
    Sorry am not making these for sale but the details and micro controller software will be freely available to anyone that wants it.

    Now I have to make the display and alarm bit.
    Bob, The Bicton Men's Shed has designed a system using a 4PDT 12v relay, a sensor activates the relay which then latches on through one contact, another activates a buzzer, the third shuts down the VFD / Dust extractor by being in series with the remote ON switch. When the DE stops the sensor resets but because the relay is self latched it stays in the alarm state until a push button in the relay latching circuit is pressed. Our problem is that the sensor is activated when the cyclone "overflows" into the exhaust ducting, so there is a clean up required after the bin has been emptied!

    So when you have finalized your sensor design we would interested in using it to replacing our sensor.

    Regards,
    Arie.
    Arie.

  5. #4
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    Quote Originally Posted by Breezy View Post
    Bob, The Bicton Men's Shed has designed a system using a 4PDT 12v relay, a sensor activates the relay which then latches on through one contact, another activates a buzzer, the third shuts down the VFD / Dust extractor by being in series with the remote ON switch. When the DE stops the sensor resets but because the relay is self latched it stays in the alarm state until a push button in the relay latching circuit is pressed. Our problem is that the sensor is activated when the cyclone "overflows" into the exhaust ducting, so there is a clean up required after the bin has been emptied!

    So when you have finalized your sensor design we would interested in using it to replacing our sensor.

    Regards,
    Arie.
    No worries Arie.

    I'll post updates here so you will know where it's at.

  6. #5
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    Hi Bob, "Given how deaf the men's shed members are it will need to be LOUD", would it be possible to connect a flashing light to the system? I find a flashing light better in noisy conditions.
    Kryn
    To grow old is mandatory, growing up is optional.

  7. #6
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    Flashing light - good idea - will look into the cost.

  8. #7
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    TBH I do not see what the problem is apart from slack management. If the bin is emptied every day before the shed is closed the problem goes away and that is down to management and developing good habits just like sweeping the floor is a good habit.
    CHRIS

  9. #8
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    Quote Originally Posted by Chris Parks View Post
    TBH I do not see what the problem is apart from slack management. If the bin is emptied every day before the shed is closed the problem goes away and that is down to management and developing good habits just like sweeping the floor is a good habit.
    I guess it depends on the sheds activities but a large bin should not need to be emptied daily especially if it only contains a small amount of sawdust and very large bin should not need to be emptied even if it is half full because whether its emptying half bucket or half a bin of sawdust, especially out of a large bin, on a daily basis just results in unnecessary dust exposure to the person emptying the bin.

    BTW I know what you mean about regular maintenance but sweeping the floor on a daily basis also increases dust exposure and its better to vac with an external vac )

    The full size wheelie bins used at the shed where I am a member usually lasts anywhere from a week to 4 weeks.
    When its full we just wheel bin to the kerb and replace it with a spare so there's minimal dust exposure involved.
    However we only have 3 bins and a weekly rubbish collection service so we cannot replace daily.

    The problem then comes down to seeing how much sawdust is in the bin.
    This means unlocking the DC enclosure and peering at the transparent windows on the side of the bins which are covered in dust on the inside so its impossible to see how much is there.
    To really find out we have to open up the bin lid and that just takes longer and sometimes the lid is not replaced properly and that leads to more problems so we stopped members fiddling with the lid.
    A set of bathroom scales under the bin is what I initially proposed although it still requires someone to open up the enclosure and actually check, and we all know how well any sort of checking happens at the mens shed where I am a member. This is why I came up with the remote bathroom scales idea.

  10. #9
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    No matter how you couch it the fix is not needed because it should be a daily job like cleaning before everyone leaves. Any way you put it does not change that and good house keeping starts with good management and a bin full sensor only reinforces bad habits as they know that the sensor tells them when it needs emptying. I must be used to Mens Sheds that do this sort of thing routinely every day and I thought it would be the same elsewhere.
    CHRIS

  11. #10
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    Being involved with a shed, everyone has different ideas on what/how it should be done, depending on who's in charge on the day. A some of Bobs previous posts will detest, some in charge will do the right thing, while others will say it's unnecessary to do it every day or weekly or what ever, regardless if it's cleaning, maintenance of machines, restocking etc.
    Kryn
    To grow old is mandatory, growing up is optional.

  12. #11
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    The Bicton Men's Shed uses a small wheelie bin and sometimes we can fill it several times in a session when we are using the thicknesser. We also check the bin at the start of a session and empty it at the end.


    Sent from my iPad using Tapatalk
    Arie.

  13. #12
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    I think it is a good idea even for a hobby system and very simple compared to rotating paddle sensors. Very easy to forget to check the collection bin / barrel when jointing and planing a large amount of stock. It might be handy for a home shop to be able to select 2 or 3 weights to taylor the waste weight to what is being cut. Pine shavings verses hardwood shavings from the planer verses MDF dust off a CNC router.

    Pete

  14. #13
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    Quote Originally Posted by QC Inspector View Post
    I think it is a good idea even for a hobby system and very simple compared to rotating paddle sensors. Very easy to forget to check the collection bin / barrel when jointing and planing a large amount of stock. It might be handy for a home shop to be able to select 2 or 3 weights to taylor the waste weight to what is being cut. Pine shavings verses hardwood shavings from the planer verses MDF dust off a CNC router.

    Pete
    The system I've set up allows you to set the alarm trigger weight anywhere from about 4kg to 50 kg so you could adjust the trigger level up or down depending on what you were doing.
    I would suggest just setting the alarm level conservatively - you can always take a look at how much is in the bag and if there was enough room just add a few kgs to the alarm level as needed.

    Smaller sensors (10kg max rating) are available that could be placed in a triangle under a base under a single bag DC that would accurately measure the weight.
    While 3 sensors will give more accuracy the cost will add up.

    Most folks with collection bags allow their bags to over fill. Collection bag should be emptied when it is between 1/2 - 2/3rds full. It depends what processes have been used but even before then the filters are likely to be well and truly clogged. As the sawdust level rises more and more of the sawdust is swirling around in the top bag and really clogging the filters.

  15. #14
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    Quote Originally Posted by Chris Parks View Post
    No matter how you couch it the fix is not needed because it should be a daily job like cleaning before everyone leaves. Any way you put it does not change that and good house keeping starts with good management and a bin full sensor only reinforces bad habits as they know that the sensor tells them when it needs emptying. I must be used to Mens Sheds that do this sort of thing routinely every day and I thought it would be the same elsewhere.
    All I did was put a perspex window in the front of my collection drum. I can see how full it is regardless of the weight of the material. I can see if it is on fire.

    Low-tech of course, and I have to check it. It won't scream for attention but it works just fine. Never needs winding, no batteries to change and 100% reliable. I have never let the collection drum overfill.

    Cheers

    Doug
    I got sick of sitting around doing nothing - so I took up meditation.

  16. #15
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    Quote Originally Posted by doug3030 View Post
    All I did was put a perspex window in the front of my collection drum. I can see how full it is regardless of the weight of the material. I can see if it is on fire.
    Low-tech of course, and I have to check it. It won't scream for attention but it works just fine. Never needs winding, no batteries to change and 100% reliable. I have never let the collection drum overfill.
    I should have indicated that it's not intended for anyone that can see their DC - I would certainly hope they can use their eyes in that situation. It's of more significance to folks that have their DC in an enclosure either inside or outside their shed. We also have transparent windows in the sides of our collections bins but they get covered in dust and its still difficult to see the sawdust level.

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