Post by thread:[EE] shake, rattle and roll

I have an application that I was thinking of using an accelrometer for, but now I wonder if there is a less expensive and easier method. Essentially I want to wake up the circuit if the box is picked up. So I guess more of a movement sensor....its known by another name, as googling hasn't been all that helpful so far. --------------------------------- Yahoo! for Good Click here to donate to the Hurricane Katrina relief effort.

Alan, On Fri, 23 Sep 2005 12:54:55 -0700 (PDT), alan smith wrote: > I have an application that I was thinking of using an accelrometer for, but now I wonder if there is a less expensive and easier method. Essentially I want to wake up the circuit if the box is picked up. So I guess more of a movement sensor....its known by another name, as googling hasn't been all that helpful so far. Do you mean a tilt switch? At one time made by using a blob of mercury that shorted a pair of contacts, or didn't, according to its angle to the ground. Nowadays they are mercury-free, so much less fun! :-) Cheers, Howard Winter St.Albans, England

probably thats what I mean, I just haven't found exactly what...so would a tilt switch operate if the unit was simply picked up or does it need to actually tilt Howard Winter <spam_OUTHDRWTakeThisOuTh2org.demon.co.uk> wrote:Alan, On Fri, 23 Sep 2005 12:54:55 -0700 (PDT), alan smith wrote: > I have an application that I was thinking of using an accelrometer for, but now I wonder if there is a less expensive and easier method. Essentially I want to wake up the circuit if the box is picked up. So I guess more of a movement sensor....its known by another name, as googling hasn't been all that helpful so far. Do you mean a tilt switch? At one time made by using a blob of mercury that shorted a pair of contacts, or didn't, according to its angle to the ground. Nowadays they are mercury-free, so much less fun! :-) Cheers, Howard Winter St.Albans, England

Alan, Tilt switch... On Fri, 23 Sep 2005 14:40:33 -0700 (PDT), alan smith wrote: > probably thats what I mean, I just haven't found exactly what...so would a tilt switch operate if the unit was simply picked up or does it need to actually tilt Well it needs to experience a change in gravity that feels like tilting - either actual tilting or accelerating horizontally in the right direction would do it - but I can't think of anything (even an accelerometer) that would reliably indicate being picked up. But If you do it slowly enough, you could defeat almost any non-contact sensor. Have you considered just having a switch underneath, bearing on the surface it's resting on, so that it operates when lifted off it? Cheers, Howard Winter St.Albans, England

On Sep 23, 2005, at 12:54 PM, alan smith wrote: > Essentially I want to wake up the circuit if the box is picked up. > So I guess more of a movement sensor. The standard in toys is a spring, fixed at one end, as one contact, an a central rigid conductor as the other contact, but you'd be very challenged to make such a thing respond to being "picked up" (as opposed to shaken, or thrown against the floor.) Tilt sensors using mercury or balls likewise require tilting. BillW

> probably thats what I mean, I just haven't found exactly > what...so would a tilt switch operate if the unit was simply > picked up or does it need to actually tilt Alan, they'd be called pick-up switches otherwise ;-)) Mercury tilt switches aren't particularly sensitive, although you can get them in a variety of degrees. The simplest for you might be a pendulum. It's the type of sensor used as a "TILT" switch in pinball machines and motorbike alarms. Basically a wire hangs freely in the middle of a wire ring. If the two touch, the circuit is completed. Something you could make yourself. The smaller the ring or greater its distance from the wire pivot, the more sensitive the alarm. The best wire to use is gold-plated, because it doesn't get a non- conducting oxide layer as other metals would over time, and you can get that free (or very cheap) as scrap from anyone who electro- plates for jewellers or maybe even a manufacturing jeweller

On Fri, 2005-09-23 at 12:54 -0700, alan smith wrote: > I have an application that I was thinking of using an accelrometer > for, but now I wonder if there is a less expensive and easier method. > Essentially I want to wake up the circuit if the box is picked up. So > I guess more of a movement sensor....its known by another name, as > googling hasn't been all that helpful so far. Vibration sensor? They're used in car alarms and the like.. About UK£1 from RS.. I used one in a car alarm project.. It was a tad too sensitive though and tended to resonate with lorries and loud bass-boxes..and people kicking the bumper :) The action of picking a vibration sensor up will almost certainly set it off. I think they consist of a tiny ball mounted vertically on a spring, in a gold-plated dome. When one touches the other the circuit is made. Or that's what it sounds like when you shake 'em... Cheers, Tim.

>> Have you considered just having a switch underneath, bearing on >> the surface it's resting on, so that it operates when lifted off it ? > > eg a mouse microswitch - very low operation force I have just seen another good idea (does not work in dark) a cds photocel mounted in the bottom Peter van Hoof

How about a shock/vibration sensor from a car-alarm? Some of these I've seen have adjustable sensitivity. There are also shock/vibration sensors for house/building windows. Cheers, -Neil. On Friday 23 September 2005 02:54 pm, alan smith scribbled: {Quote hidden}> I have an application that I was thinking of using an accelrometer for, but > now I wonder if there is a less expensive and easier method. Essentially I > want to wake up the circuit if the box is picked up. So I guess more of a > movement sensor....its known by another name, as googling hasn't been all > that helpful so far. > > > --------------------------------- > Yahoo! for Good > Click here to donate to the Hurricane Katrina relief effort.

You can make your own with a piezo disk, a ball bearing and small capsule, like a plastic cover that fits over a tubular table leg, or even a cooldrink cap. The ball rests on the smooth side of the piezo, and when someone picks the device up, the ball bearing rolls to the side and,.. smack, generates a good many volts. Needs some filtering because it's very sensitive(but narrowband) to general floor noise. Regards Roland {Quote hidden}> >On Friday 23 September 2005 02:54 pm, alan smith scribbled: >> I have an application that I was thinking of using an accelrometer for, but >> now I wonder if there is a less expensive and easier method. Essentially I >> want to wake up the circuit if the box is picked up. So I guess more of a >> movement sensor....its known by another name, as googling hasn't been all >> that helpful so far. >> >> >> --------------------------------- >> Yahoo! for Good >> Click here to donate to the Hurricane Katrina relief effort. > > Regards Roland Jollivet

> I have just seen another good idea (does not work in dark) > a cds photocel mounted in the bottom Commonly found as a drawer alarm, can be used in a very low power configuration. If quiescent is an issue, a metallic contact type can be the trigger for a self-latching PSU switch, so no power at all is consumed until there's a contact

Thanks for all the interesting suggestions. The photocell idea wont work because it may be dark, the the primary reason to have this is to backlight a display if the unit is picked up. The other ideas of homebuilt won't work because this is going to be a high volume (he hopes) product, so it needs to be simple. A switch on the bottom wont work because there is no guarantee it will always sit flat on a surface. Even if the unit needs to be jostled a bit to turn on the backlight is fine, the user will just know if they do that enough the backlight will turn on. OK...someone is going to suggest a button for the backlight. Only issue with that is if the person has impaired vision, they wont be able to find a button. I might be able to solve this by other means....this just seemed to be a good way to momentarily backlight a display. Gus Salavatore Calabrese <.....gscKILLspam@spam@omegadogs.com> wrote: reed switch and magnet that falls away ( could be hinged ) AGSC

On Sep 26, 2005, at 9:42 AM, alan smith wrote: > Even if the unit needs to be jostled a bit to turn on the backlight is > fine In that case, one of the spring or rolling ball based switches ought to work fine. I was worried you wanted to detect motion that the "user" was trying to keep undetectable. The other interesting idea is some sort of capacitive or noise-pickup "touch switch", so the backlight would go on whenever you touched it. BillW

true....both good ideas....but needs to be cheap...or almost free. I've got a couple of other ideas as well...just need some 'thinkin' time to figure them out. Thinkin time is where you are sitting feet up..staring out in the abyss and the boss walks by and says....wake up...get to work.... William Chops Westfield <westfwKILLspammac.com> wrote: On Sep 26, 2005, at 9:42 AM, alan smith wrote: > Even if the unit needs to be jostled a bit to turn on the backlight is > fine In that case, one of the spring or rolling ball based switches ought to work fine. I was worried you wanted to detect motion that the "user" was trying to keep undetectable. The other interesting idea is some sort of capacitive or noise-pickup "touch switch", so the backlight would go on whenever you touched it. BillW

More ideas piezo strip parallel to table, inside box with small weight on end. Acceleration causes voltage which is detected. Also detects earthquakes. resistive flex strip set up the same way. Acceleration causes resistive change. AGSC

On 9/28/05, Gus Salavatore Calabrese <.....gscKILLspam.....omegadogs.com> wrote: > > More ideas > > piezo strip parallel to table, inside box with small weight > on end. Acceleration causes voltage which is detected. > Also detects earthquakes. Yeep. But everything is piezo is also more or less pyro. So avoiding heat variation which is increasing the error or it must be compensated. And will be a voltage variation for an acceleration variation. Not easy for an accurate measurement. And good only for great earthquakes where anyway does not care, you'll don't be allive to monitorise the signal... cheers, Vasile {Quote hidden}> > resistive flex strip set up the same way. Acceleration causes > resistive change. > > AGSC > > > > > > > -