Jerk Sensor?

Hi everyone,

I’m new here and I hope i’m not posting in the wrong forum.

I’m currently thinking of making a watch that responses to the jerk of the arm. Everytime a jerk is detected some graphics will be displayed.

However, I have no ideal what type of sensor is able to fulfill my requirements…

Any suggestions?

Thanks!

You could use an accelerometer.

  • Ben

Everytime a jerk is detected some graphics will be displayed.

Could be helpful for some forums I frequent. :smiley:

On a more useful note, the big issue with any such sensor (electronic or mechanical) would be how (un)sensitive it needs to be to avoid false positives. Another recent forum thread here talked about using a small spring to detect movement.

–Phil.

If your “jerk” is in a single plane, a “mercury” (tilt) switch might work. Small and cheep anyway.
http://www.action-electronics.com/switches.htm#Mercury

Hi bens and follower! thanks for the reply!

I don’t need all of the features of the accelerometer and i don’t think it comes cheap. Furthermore, I intend to have it attached on a wristband or sorts, so the form factor would be a consideration for me. Perhaps there’s a small and cheap accelerometer around?

Anyway, I was thinking along the lines of sandwitching a flexible metal strip between two contacts… so whenever the movement is great enough, it causes the flexible strip to touch one of the contacts.

But i was wondering if there are any commerial products out that can fit my requirements…

Phil, would it be possible to give me more details about the other post so I can search it out? Can’t seem to find it…

Thanks so much!
;D

If your “jerk” is in a single plane, a “mercury” (tilt) switch might work. Small and cheep anyway.
action-electronics.com

Hi there,

I was thinking of mounting the sensor on a wrist band, and only activates when a large enough jerk is detected. so i guess a tilt switch is out?

thanks anyway… =)

If size is an issue, it seems like you’re going to need to use surface-mounted components to fit the sensor and microcontroller along with supporting electronics, in which case I don’t think you’ll get much smaller than an accelerometer IC:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=MMA7260QT-ND

It’s more than you need, but it’s quite small (6mm x 6mm x 1.5 mm QFN) and you can buy a single unit from digikey for $3.18. That seems pretty small and cheap, but the catch is that it’ll be difficult to solder, which is why people typically purchase them on breakout boards, and it’s a 3.3V part.

A switch made from a spring would also work, but I don’t know of any prebuilt solutions (I’m not saying there aren’t any out there, just that I can’t help you with finding them) and I think making your own could be a bit difficult mainly because you’d need to finely calibrate the mechanics for it to work. There isn’t going to be much difference between the forces it experiences from natural arm swings and the forces it experiences as you shake your wrist more violently. At least an accelerometer would let you do the calibration in software. Also, I could easily see a homemade solution being bigger than an accelerometer IC, but it would be much easier to solder and might prove more satisfying to you.

  • Ben

You could try using two mercury switches in such an orientation that it took a quick flip of the wrist to activate them within a certain period of time.

–Phil.

If size is an issue, it seems like you’re going to need to use surface-mounted components to fit the sensor and microcontroller along with supporting electronics, in which case I don’t think you’ll get much smaller than an accelerometer IC:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=MMA7260QT-ND

It’s more than you need, but it’s quite small (6mm x 6mm x 1.5 mm QFN) and you can buy a single unit from digikey for $3.18. That seems pretty small and cheap, but the catch is that it’ll be difficult to solder, which is why people typically purchase them on breakout boards, and it’s a 3.3V part.

A switch made from a spring would also work, but I don’t know of any prebuilt solutions (I’m not saying there aren’t any out there, just that I can’t help you with finding them) and I think making your own could be a bit difficult mainly because you’d need to finely calibrate the mechanics for it to work. There isn’t going to be much difference between the forces it experiences from natural arm swings and the forces it experiences as you shake your wrist more violently. At least an accelerometer would let you do the calibration in software. Also, I could easily see a homemade solution being bigger than an accelerometer IC, but it would be much easier to solder and might prove more satisfying to you.

  • Ben

Thanks so much ben! I never knew accelerometers come in such small packges! Seems like a possible candidate… Thanks for the suggestion!

You could try using two mercury switches in such an orientation that it took a quick flip of the wrist to activate them within a certain period of time.

–Phil.

Thanks Phil! the idea of using two mercury switch is so clever! i’ll go do more research on it… =)

Hey, I was thinking of something similar, a watch with multiple functions, and a Jerk one, kind of a pedometer for your lonely nights ^^
Come to think of it : what kind of sensor is in a pedometer?
Anyway, I was going for the accellerometer on my watch.

Ben’s mention of a spring switch would work. I found one the other day in a cat toy. Whenever you hit the toy with enough force it starts flashing. You can get the toy for about 5 bucks and then just harvest the materials from it. You could even try one of those bouncy balls that light up when you bounce them.

Ben’s mention of a spring switch would work. I found one the other day in a cat toy. Whenever you hit the toy with enough force it starts flashing. You can get the toy for about 5 bucks and then just harvest the materials from it. You could even try one of those bouncy balls that light up when you bounce them.

Or, click the link I just posted, and get just the sensor for way less.

Ben’s mention of a spring switch would work. I found one the other day in a cat toy…

Or, click the link I just posted, and get just the sensor for way less.

It’s quite useful to mention what a link goes to when posting-- I’ve been rickrolled’d and goatse’d enough…

Also, “click the link… and get…”? Thats two commands in a row-- suggestions are often more constructive than commands. Many people do not like being told what to do. You tripped the jerk sensor with that line, for sure…:wink:

Very useful link, though, thanks for that:

$1 Tiny Vibration/Tilt Switch:

Many people do not like being told what to do.

It did work, though. :smiley:

Anyway, here’s a tutorial [including a basic sketch].
http://www.arduino.cc/en/Tutorial/AccelerometerMemsic2125

the rolling-ball-tilt switch is cheap, and it unlike mercury it does not leech into the environment and get accumulated in fish, ultimately poisoning the people who eat them! Mercury is really bad news.

D