Hello!

I've been looking everywhere for a solution but couldn't find one. I would like to close a simple circuit when a weight (~20 lbs) is placed on the switch (and open the circuit when the weight is removed). What's the correct way to do this? Preferably a switch I can buy as opposed to building one, footprint about the size of a penny would be great.

Thanks for the help!
Nate

 

Your problem is a Mechanical-Design problem first,
then the Electrical part can easily be worked-out.

For instance, You mention that it needs to be the size of a Penny.
Well, what weighs ~20-pounds and is the size of a Penny ?
What are You weighing ?, Cardboard-Boxes ?, Liquids ?, estimating quantity by weight ?
How large is the item to be weighed ?

How much Travel, or downward-Motion is acceptable ?, zero ?, 1/8-inch ?, 1/2-inch ?

What limits the downward travel to prevent damage to the Switch ?

What is the Frequency that this Switch must operate reliably at ?

What will be the average number of On/Off-Cycles that are likely to occur per day ?

What will prevent "Switch-Bounce" ?, ( multiple, unintentional, On/Off Switching-Cycles )

How precise does the weight need to be to cause the Switch to change states ?
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Hello!

I've been looking everywhere for a solution but couldn't find one. I would like to close a simple circuit when a weight (~20 lbs) is placed on the switch (and open the circuit when the weight is removed). What's the correct way to do this? Preferably a switch I can buy as opposed to building one, footprint about the size of a penny would be great.

Thanks for the help!
Nate

Almost any but not all “SIngle Pole Single Throw Momentary Switches” would do. Search for them in your favorite electronics supplier or even Amazon.

 

Here's one with 6 to 8 lb activation force. You might use this to tract down a manufacturer and go to their website.

https://www.ebay.com/itm/2553533487...044&customid=93a31f2057341e1618187bf92c1a57bf

 

Your requirement is not at all clear. Some responders seem to be assuming that a lesser weight should not trigger it, but I don’t think that is your intent. The way I read it is that an object weighing about 20 lbs will be placed in a particular place and you only need to know if that object is present or not.

So, please clarify your intent.

If it is what I think, I would use a lever action microswitch. The are very commonly used to sense the presence of an object.

 

Your problem is a Mechanical-Design problem first,
then the Electrical part can easily be worked-out.

For instance, You mention that it needs to be the size of a Penny.
Well, what weighs ~20-pounds and is the size of a Penny ?
What are You weighing ?, Cardboard-Boxes ?, Liquids ?, estimating quantity by weight ?
How large is the item to be weighed ?

How much Travel, or downward-Motion is acceptable ?, zero ?, 1/8-inch ?, 1/2-inch ?

What limits the downward travel to prevent damage to the Switch ?

What is the Frequency that this Switch must operate reliably at ?

What will be the average number of On/Off-Cycles that are likely to occur per day ?

What will prevent "Switch-Bounce" ?, ( multiple, unintentional, On/Off Switching-Cycles )

How precise does the weight need to be to cause the Switch to change states ?
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Thanks for the response! And you're right, more of a mechanical problem. Here's some more detail.

What are you weighing?:
I'm "weighing" the force put on a D-ring by a dog pulling against his leash (leash attached to D-ring, D-ring attached to said dog's neck via collar)

What is 20 lbs and the size of a penny?:
A D-ring being pulled on by a difficult dog and his frustrated, electro-mechanically-inclined owner.

How much travel is tolerable?:
I'm flexible on this but the device (switch) will need to sit in the collar, under the ring so I would think no more than 1/4 inch in overall thickness when not under load which would suggest ~1/8 inch travel.

What limits downward travel to protect the switch?:
Good question, I would hope that a purchased switch that took 20lbs of moment to operate cold withstand 200lbs but something I would need to consider if I have to build something.

What is the frequency this switch will need to operate at?:
I would think 1Hrz would be plenty fast enough.

How precise does the weight need to be measured?:
I would think 20lbs +/- 10lbs would be acceptable although 1lb of variability seems reasonable.

What will the average number of on-off cycles be?:
Depends on the dog, if he'd listen to his training zero but I wouldn't be asking this question if he listened to his owner haha. I would think about 30x on a walk, hopefully decreasing over time.

Question by other regarding disconnecting the circuit:
I would want the circuit to open immediately upon force < 20lbs (dog stops vibrating as soon as he stops pulling on me, thus dog learns not to pull on me).

Esd disclosure:
I've built this circuit around a vibrating motor, not an electronic shock, no one will be shocked by this device.

 

Almost any but not all “SIngle Pole Single Throw Momentary Switches” would do. Search for them in your favorite electronics supplier or even Amazon.

Thanks! Will do!

 

Best idea I have right now is a flush washer and a flat washer isolated by a rubber washer that would make contact when the rubber was compressed.

 

Please don't ask me.
A dog is not a toy.
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Thanks for the response! And you're right, more of a mechanical problem. Here's some more detail.

What are you weighing?:
I'm "weighing" the force put on a D-ring by a dog pulling against his leash (leash attached to D-ring, D-ring attached to said dog's neck via collar)

What is 20 lbs and the size of a penny?:
A D-ring being pulled on by a difficult dog and his frustrated, electro-mechanically-inclined owner.

How much travel is tolerable?:
I'm flexible on this but the device (switch) will need to sit in the collar, under the ring so I would think no more than 1/4 inch in overall thickness when not under load which would suggest ~1/8 inch travel.

What limits downward travel to protect the switch?:
Good question, I would hope that a purchased switch that took 20lbs of moment to operate cold withstand 200lbs but something I would need to consider if I have to build something.

What is the frequency this switch will need to operate at?:
I would think 1Hrz would be plenty fast enough.

How precise does the weight need to be measured?:
I would think 20lbs +/- 10lbs would be acceptable although 1lb of variability seems reasonable.

What will the average number of on-off cycles be?:
Depends on the dog, if he'd listen to his training zero but I wouldn't be asking this question if he listened to his owner haha. I would think about 30x on a walk, hopefully decreasing over time.

Question by other regarding disconnecting the circuit:
I would want the circuit to open immediately upon force < 20lbs (dog stops vibrating as soon as he stops pulling on me, thus dog learns not to pull on me).

Esd disclosure:
I've built this circuit around a vibrating motor, not an electronic shock, no one will be shocked by this device.

It wouldn't be too difficult to build a sleeve that almost any pushbutton switch could stick into -- but some decent travel would be good. The sleeve would basically be a suitable spring with a washer on it. You could build in the ability to adjust the spring position so that the switch get activated at the desired about of force.

A simple lever system could also be built into a handle and that would probably be easier to build.

 

All you need is a standard pushbutton switch and a spring
https://www.weltroniker.de/DB-Pool/dip_dts2_2016-09-09_a9bb.pdf
Choose a spring with the required "rate" so that when it is compressed the switch gets pressed. Place the spring over the button.
The switches are available with several different activating forces.
I used the technique to make footswitches. Careful positioning of the switch and spring will allow you to prevent damage by the application of too great a force.
Another alternative is the V3 or V4 microswitch. They are available with different actuating forces, and loads of accessories to join to all sorts of mechanisms.

 

A D-ring being pulled on by a difficult dog and his frustrated, electro-mechanically-inclined owner.

Wow! I never would have guessed that from your initial post. Hiding that information would have made this thread completely useless.

Thanks for giving us the details quickly, you saved us all a lot of time and frustration, unlike many other people with “secret” projects.

Just a nitpick: using the correct word, ”force,” instead of “weight” would have been less misleading.