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Movement detection

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2010 - » Archive through 25 January, 2012 » Movement detection « Previous Next »

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bruce
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Username: bruce

Post Number: 732
Registered: 04-2008

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Posted on Sunday, 22 January, 2012 - 10:39 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi,
I have a PIC which is flashing some LEDs ( yup, no-one ever thought of that before, I bet ).

The LEDs are in rows and the idea is to flash the rows sequentially. However, I really want the rate at which the sequence is accomplished to respond to movement: the more vigorous the movement, the faster the rate.

An obvious method ( well, to me )is one of those 'footstep counters', although I'm not sure the mechanical counter would work well ( I could be wrong, as I have been wrong before ). Didnt someone glue a small weight on a piezo sound module to get a movement detector?

Whatever the output, it would probably need to be digital, or digitized in some way, because it will be a 'button' input.

Come on guys, thinking caps on: I expect the best idea to appear on "Dragon's Den".

bruce
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mikehibbett
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Post Number: 1351
Registered: 04-2005


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Posted on Sunday, 22 January, 2012 - 10:57 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Use a tilt switch. Or better, two. £1.20 from farnell.

It's what security products use to detect motion (speaking from experience)

The switch is a small amount of mercury inside a small tube with two contacts at one end. Simple and effective.

Piezo's require impact; you could put it in a small box with a few ball bearings. Hum... that sounds interesting....

Piezo's are like £1.50 from maplin, but beware - they can output anything from a few hundred millvolts to 100V!
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cjaysharp
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Post Number: 168
Registered: 06-2010

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Posted on Sunday, 22 January, 2012 - 12:38 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Buy a Wii Motion Plus controller? I2C interface and three axis I think?
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kolbep
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Username: kolbep

Post Number: 154
Registered: 05-2009


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Posted on Sunday, 22 January, 2012 - 01:50 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

When I was a young lass, (Only about 20 years ago), I used to have a toy axe, that used a small spring soldered on the pc board. This spring was inside a metal cylinder which was also on the board (sort of like a hollowed out capacitor without the top and bottom).

Shaking the axe (and by hitting my sister on the head), it caused the spring to contact the cylinder, which triggered the chip to make a screaming sound.

Perhaps you can do a similar arrangement, and get the micro to count the contact bounces (This arrangement could easily be put onto a digital input on the micro), the more bounces the micro reads, the more vigirous the shaking was

P
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kolbep
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Post Number: 155
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Posted on Sunday, 22 January, 2012 - 01:51 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Put a blob of solder on the top of the spring, and it will have more inertia
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terry
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Post Number: 646
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Posted on Sunday, 22 January, 2012 - 02:39 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Surprising to learn you were a young lass!!


Terry
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kolbep
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Username: kolbep

Post Number: 156
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Posted on Sunday, 22 January, 2012 - 02:56 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Well, next month I will be 30. For me that is Over the Hill and Around the bend.
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bruce
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Post Number: 736
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Posted on Sunday, 22 January, 2012 - 05:15 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Peter, this is no place to discuss your sex-life.

Actually, chaps, I lied to you: the movement detector I need is ( I think) going to have to be a bit more sophisticated. First, the LEDs are going to have to run through their 5-step sequence at a resting rate of about 200 - 500 msec per step ( give or take ) This rate will have to happen even if the 'dancer' isnt moving, and mechanical movement detectors, almost by definition, produce no output at rest. Problem!

The next problem is that I want the rate of progress of the sequence ( I hope you're following this at the back ) to reach, maybe, 10 times that as an upper limit. This, I imagine, is a doddle with sound, but movement? I dont see how movement ( say, dancing ) could generate a 'signal' over a range of 10-fold. At a guess, even 5-fold might be enough, but I suspect the range in practise would be more 'moving' or 'not moving'.

Another brilliant idea crashes to the ground.

bruce
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joe
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Post Number: 1270
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Posted on Sunday, 22 January, 2012 - 05:25 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Bruce, I'm having a hard time following this invention of yours... but then I've got a cold so that could be it.

You want to detect a person moving around.

You want a chain of 5 LEDs.

When the person is idle, you want to step to the next LED in sequence every 200 - 500 ms.
However, the more they move around, the faster the step (or the slower the delay between steps if you prefer). A ten-fold increase in speed of LED stepping wound be aorund 20 - 50ms delay between steps.

I assume you only want 1 LED on at a time.

Is this right ?

I'm not going to ask "why" you want this, as I have a feeling the answer will scare me. But it sounds like an interesting techncial challange.

Regards,
Joe
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twintub
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Post Number: 214
Registered: 02-2007

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Posted on Sunday, 22 January, 2012 - 11:19 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Kolbep,

I think you should clarify your 'satus' before you get yourself into trouble; Surely you were once a young 'lad' not a 'lass'!
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kolbep
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Username: kolbep

Post Number: 157
Registered: 05-2009


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Posted on Monday, 23 January, 2012 - 04:40 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

So thats what they were on about.
Guess that was the forums first fail of the year...

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