Hello

I am doing a project to create a small system for elderly. the system should detect if they have fall and send an SMS message.

I have been asked to use accelerometer for the purpose of the system
the issues I am facing are as follow:

1- how to choose a suitable sensitivity
2- found a device with some sensitivity / G, but isn't it that
the plane we usually move on will always be 1G. is 1G ~10m/s^2
if that's true how would I be able to detect the elderly falling as different people will have different speed and acceleration is the rate of change of speed (Velocity).

I welcome any pointers in the matters Thanks for your Help

Hey, Im not an expert but I used some accelerometers in my masters project a few years ago.

1- The better the sensitivity generall the better the accelerometer- it's a measure of output (voltage) change with regards to input (acceleration) change, so really limiting factors should really be cost and whatever input your microcontroller (or whaterver control your using) can accept.

2- When someone falls I assume your accelerometer will not stay 'level'. When this happens it will experience a change in gravity relative to the angle through which it tilts

sorry it's not more in depth, I don't have much time atm

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Andrew Packwood MEng

Thanks very much every little helps as they say, if you can point me toward some reading material that can be useful.

I think that there is a good texas instruments pdf (Acceler1.pdf - google is your friend) that takes you through all of the basics to do with accelereometers, the application your using them for shouldn't involve anything overtly complicated, they are fairly well documented so there are probably heaps of books out there with in-depth application notes.

There are many different types of accelerometer so I won't go into detail about how they work though most are capacative and piezoelectric. For the most part functionality involves varying the output voltage in a linear fashion with respect to the 'tilt' angle it goes through. That is why there are 1/2/3 axis accelerometers out there, you need to decide how many axis' are worth measuring and what kind of acceleration around these axis will represent a fall. Once you've done that your control circuitry should be reasonably straight-forward.

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Andrew Packwood MEng

I don't think you can just use an accelerometer by itself, since there are a number of factors to consider.

a) Rate of fall is incredibly difficult to ascertain, and cannot be used in isolation.
b) may slip off a chair and slide to the ground, unable to get up.
c) may bend over to pick something up, unable to regain a sitting or standing pose after, and lower themselves to the ground.
d) Stroke or heart attack patients may lower themselves to the ground under a controlled fall.
e) A person may lean rapidly from a chair to pick something up, but not fall over. Depends where the sensor is located.

The list goes on, from personal experience with an ageing Dad (RIP), God bless.

Suggest some other devices for detection along with accelerometer, placed at hip height.