shock detection

Just measure the deformation of the case ?:-)

...Jim Thompson

Why would you care about free fall? It's not the fall that kills your instrument, it's the sudden stop at the end.

It's not necessarily an appropriate job for electronics.

Cheap zero-power technology:

Best regards, Spehro Pefhany

How do you plan on measuring free fall? This is probably impossible for you. Netwon and Einstein say that free fall is an inertial frame of reference so there is no method that can measure it directly. Any method doing so must use something about the surroundings(which almost surely = air resistance).

In any case if your handhelds cost $25k+ then I'm sure you make enough money so that you can hire someone to try and solve the problem.

As far as impact, which seems to be what you actually need, take a look at

But again, if your selling a "handheld" for $25k+(what, is it made of solid gold?) then you can afford to hire a real scientist to do the work(or are you that "scientist" that was hired?).

The Brat dropped her Dell laptop yesterday, and lunched the hard drive, including a powerpoint presentation that took 8 hours to do and is due today. She called for help. I told her to head for Wal-Mart, get a new pc, and start over. They had DElls and a Sony Vaio available, and called me from the Wal-Mart and asked me which to buy. The Sony of course. It has mems accelerometers inside that detect zero-G and retract the disk heads before impact.

0G = falling

John

"Michael" skrev i en meddelelse news: snipped-for-privacy@57g2000hsv.googlegroups.com...

Calibrated glass tubes are often used - if they break, there was a shock of at least X g.

Either measure it - or don't worry about it because then it is not important.

meddelelsenews: snipped-for-privacy@57g2000hsv.googlegroups.com...

We need to have a time stamp (to be able to properly assign blame ;o) ) - glass tubes won't do. I do not know: a. "how much is too much?" b. How to keep this system running for, say, two months between recharges on whatever tiny volume available for the battery. The minimum I will need (I have found so far is) ~1..1.5Amp-hour cell. It's not tiny... :o(

Hobo:

John

You just need a loose wire.

The Fonz would punch the side of a jukebox and it would start working.

D from BC

You are quite serious when you say that?

There are some large-format piezo accelerometers out there that appear to produce a big enough signal to turn on some electronics -- I did some preliminary work on this for a prospective customer. That takes care of the "big shock" case.

For free-fall, perhaps some self-centering tilt switches?

Instead of consuming power all the time, you can get this down to consuming power for each event -- but I'll bet a hand-held instrument sees a lot of free fall without seeing consequent shock; you may run out the battery from all the "whee!" events then miss the "thump!" that you wanted to capture.

Sure-- you've failed to consider that the end user may be attempting to use the product in, say, a space station, so the 0g state is indistiguishable from normal operation.

Best regards, Spehro Pefhany

Alright, so use an opto detector of some sort that watches the glass! Or a contact (metallize the glass tube?), or who knows what else... ;-)

Tim

-- Deep Fryer: A very philosophical monk. Website @

But then, if he drops it, nothing breaks!

John

air

Argh, beat me to it! But there's really no "dropping" on a space station, is there???

Well, the disgustingly easy method won't do timestamps. It is however small, cheap enough to stick on a cardboard box, and reliable - with no batteries at all.

This will monitor, but could miss an event depending on logging interval, which trades off with battery life. Could probably arrange to OEM the guts to cut the size down (take out of waterproof package). Also rather low-range for you, I guess (+-3G)

A bit large for you, but otherwise seems to do what you want:

How bout springs? F = kx, mount two opposite springs(actually 6) on a ball then any accelleration will compress one and extent the other... the amount of acceleration being proportional to the acceleration... i.e., F = ma = kx. (with 3 axis you'll need a better algorith as it would depend on the orientation(in this case it does too but I'm assuming lateral motion)).

I'm sure there are a bazillion ways... In fact somehow they do it with very small chips using ingenious methods. I'm sure it can be done for a few dollars?

Knowing the minimum high at which the device could potentially break would help. If its in free fall(and not thrown) from 1 feet then it will take about 0.35 s to hit the ground so one does not actually have to sample at a high rate(well, depends on what this guy wants to do).

But seriously, I don't see what real damage could come from a handheld made of solid gold. What if it is dropped? Why does it matter? Does the gold really know its in free fall?

(I'm not actually saying this is a good method... I imagine it would work on a large scale with precision components but I'm sure it probably doesn't beat your standard accelerometers in cost, size, and accuracy)

Eggs are a good source of accelerometers too... although they don't actually test acceleration ;/

air

It's sort of in free-fall continuously.

Best regards, Spehro Pefhany