Starting DC motor based on squeeze pressure.

Thread Starter

homer2121

Joined Jan 2, 2016
32
Hi, I am a newbie when it comes to electronics and circuits but would like help with an experiment I am working on.

With a round handle (aprox 15-20mm diameter) I want to be able to send a current to start a small DC motor based on how hard the handle is squeezed. I don't want the motor to run when the handle is squeezed say 5,6 or 7 on a scale of 1-10 (will take some trial and error to figure out exactly how hard that is) but if the handle is squeezed harder or lighter than that range I want it to run the motor. I am thinking I would also need a switch to turn it off so when nobody is holding it the motor isn't running. All of the components would need to fit inside the handle which will be 10-12 inches long (so all stacked on top of each other).

As I mentioned I have very little knowledge in this area but I have some battery holders with attached leads and a DC Motor. Once I get a switch and whatever else I need I really have no idea how to connect it all together. Also, based on some of the research I have done I came across piezo film sensors and thought that could possibly be wrapped around the handle but I was wondering if that is the best way to do it or if there was other options. It needs to be able to withstand a little bit of wear and tear. It won't be thrown around but could be dropped occasionally.

Any suggestions??

Thanks
 

Hypatia's Protege

Joined Mar 1, 2015
3,203
I'd go 'brute force' and interface the (unprocessed) output of a strain-gauge/pressure sensor to a uC -- You'll find that said approach's lack of imagination is abundantly compensated by versatility:cool:

Best regards
HP
 

Thread Starter

homer2121

Joined Jan 2, 2016
32
I'd use a microswitch operated by a hand-grip lever acting against a strong spring.
I will provide more info I forgot to mention so it is hopefully more clear. The handle is to run a fan when squeezed. So picture a round broom handle shape about 2cm in diameter and about 10-12 inches long. The handle is solid piece that will not deform when compressed. I may put a rubber grip over top but I just want it to detect the amount of pressure when it is squeezed and start the motor when it is squeezed either below or above the desired range. When it is squeezed within the desired range I do not want the motor to turn on. It needs to be able to detect the pressure almost everywhere on the handle which is why I initially thought I would need to wrap the handle with something like the piezo film. I do not have a picture as I have not built it yet. Does this make it more clear??

Thanks
 

Hypatia's Protege

Joined Mar 1, 2015
3,203
I will provide more info I forgot to mention so it is hopefully more clear. The handle is to run a fan when squeezed. So picture a round broom handle shape about 2cm in diameter and about 10-12 inches long. The handle is solid piece that will not deform when compressed. I may put a rubber grip over top but I just want it to detect the amount of pressure when it is squeezed and start the motor when it is squeezed either below or above the desired range. When it is squeezed within the desired range I do not want the motor to turn on. It needs to be able to detect the pressure almost everywhere on the handle which is why I initially thought I would need to wrap the handle with something like the piezo film. I do not have a picture as I have not built it yet. Does this make it more clear??

Thanks
Again, your requirements are sufficiently complex that use of a uC interrogated pressure sensor is warranted!:) --- Sometimes it happens that the easy way is the best way!!!:cool::cool::cool:

Best regards
HP:)
 

Thread Starter

homer2121

Joined Jan 2, 2016
32
Ok thanks, what are all the components I need for this and where do I get them? Also, I am assuming I will have to find someone to do the programming?

Thanks again and I apologize if these are dumb questions.
 

MaxHeadRoom

Joined Jul 18, 2013
19,747
The load cells/pressure sensors from such as Omega are very pricey, it may be possible to cannibalise one of the small Kitchen scales you can get now, they have load cells and display in a flat package for around $8-$11 etc.
Wall Mart and Ebay 361129796626
I have never opened one up yet.
Max.
 

Hypatia's Protege

Joined Mar 1, 2015
3,203
I apologize if these are dumb questions.
Nothing wrong with your questions!:)

Inasmuch as it seems you are not in possession of a uC programmer and might (understandably) wish to eschew investment in same for an experimental project --- You may be well served by an Arduino (very low cost, shallow 'learning curve') in conjunction with @MaxHeadRoom 's suggestion (above):)

Strange days! -- ME recommending Arduino?!?!:eek::eek::eek::D -- But Hey! This is the appropriate application! - To wit: Prototyping of experimental projects where 'sterling Specs' aren't at issue!:):):)

Very best regards
HP:)
 

Thread Starter

homer2121

Joined Jan 2, 2016
32
Nothing wrong with your questions!:)

Inasmuch as it seems you are not in possession of a uC programmer and might (understandably) wish to eschew investment in same for an experimental project --- You may be well served by an Arduino (very low cost, shallow 'learning curve') in conjunction with @MaxHeadRoom 's suggestion (above):)

Strange days! -- ME recommending Arduino?!?!:eek::eek::eek::D -- But Hey! This is the appropriate application! - To wit: Prototyping of experimental projects where 'sterling Specs' aren't at issue!:):):)

Very best regards
HP:)
So you believe an absolute beginner like me could build the project I describe after playing with Arduino? I know how limited my knowledge is in this area so forgive me for being a bit skeptical lol.
 

Thread Starter

homer2121

Joined Jan 2, 2016
32
We could probably come up with a little circuit to use something like these if they would meet your needs. They are pretty inexpensive. I used one once for a throttle on an electric motorcycle.
https://www.google.com/search?q=pressure+sensitive+resistor&ie=utf-8&oe=utf-8
Would I be able to use a bunch of these together all connected to the same motor? I need the sensors to cover pretty much the entire handle. Or perhaps there some a bit larger that are flexible that could be wrapped around the handle so I would only be dealing with one.

I would still need to program a microprocessor wouldn't I? To send the current when it was either squeezed too lightly or too hard?

Would arduino teach me to do that?

Thanks
 

Thread Starter

homer2121

Joined Jan 2, 2016
32
maybe like this:
http://www.digikey.com/us/en/ph/Interlink Electronics/FSR408.html
Tell us more about what you are trying to do. Maybe that will stir some better ideas. I'm concerned that if you need to cover the whole thing we may have a problem with repeatability.
Can't think of how else to explain it. I want it to be a round handle that is max 20mm in diameter. All components will need to fit inside the handle and prob have a battery holder that will slide out of the top to change them. The batteries need to be connected to a switch, and a dc motor so it will start the motor ONLY when it is squeezed either too lightly or too firmly...in between when it is squeezed medium I don't want the motor to run. I am assuming I would need to program a microprocessor to differentiate all this to the motor??

It needs to cover most of the handle bc everybody will grab it differently and in a different spot since it is round. So, would either need to be multiple sensors all around the handle or just one larger one that would wrap around the handle and be at least 8 or 10 inches wide since the handle will be about 10-12 inches long. Perhaps I should use more than one motor and use two larger sensors?? I have about 12" to stack components on top of each other inside the handle so that may be enough room??

But I still need to program a microprocessor correct?

Thanks
 

ronv

Joined Nov 12, 2008
3,770
Can't think of how else to explain it. I want it to be a round handle that is max 20mm in diameter. All components will need to fit inside the handle and prob have a battery holder that will slide out of the top to change them. The batteries need to be connected to a switch, and a dc motor so it will start the motor ONLY when it is squeezed either too lightly or too firmly...in between when it is squeezed medium I don't want the motor to run. I am assuming I would need to program a microprocessor to differentiate all this to the motor??

It needs to cover most of the handle bc everybody will grab it differently and in a different spot since it is round. So, would either need to be multiple sensors all around the handle or just one larger one that would wrap around the handle and be at least 8 or 10 inches wide since the handle will be about 10-12 inches long. Perhaps I should use more than one motor and use two larger sensors?? I have about 12" to stack components on top of each other inside the handle so that may be enough room??

But I still need to program a microprocessor correct?

Thanks
It can be done in hardware or microprocessor. Can you solder and read a schematic?
 

Thread Starter

homer2121

Joined Jan 2, 2016
32
It can be done in hardware or microprocessor. Can you solder and read a schematic?
I have never done either. But if you can tell me what needs to be done with hardware I can learn how to solder and I can get help reading a schematic. If I were to go the microprocessor route would I learn what I need to through arduino?

Which option would be cheaper?

I am willing to try the hardware option if that will achieve the desired results just need to be told what to do and then i will do what I can and get help with the rest.

Thanks
 

ronv

Joined Nov 12, 2008
3,770
I can't do it right now, but I will make a schematic tomorrow.
Maybe some other ideas between now and then.
 
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