Looking for a contact sensor

[somewhere]

Hy guy's, I have the following problem.

I need a contact sensor 80 x 80 cm which will be use outdoor.
The problem is, the sensor must dedect weight from 0,5 kg to 30 kg.
The sensor must detect in ms if it was touched or not.

My first Idea was to use a capacitive system but I don't know if there is such a big size available.
Maybe someone of you can give me a good idea.

Thanks in advance
somewhere

[bbarney]

I think your looking for a load (cell)sensor
http://www.sensorsportal.com/HTML/SENSORS/Load_Cells.htm
http://findit-fixit.sensorsmag.com/showthread.php?t=590

[Trishool]

Hy guy's, I have the following problem.

I need a contact sensor 80 x 80 cm which will be use outdoor.
The problem is, the sensor must dedect weight from 0,5 kg to 30 kg.
The sensor must detect in ms if it was touched or not.

My first Idea was to use a capacitive system but I don't know if there is such a big size available.
Maybe someone of you can give me a good idea.

Thanks in advance
somewhere

30Kg , search Loadcells there are plent and very low cost . I dont understand when you say
" The sensor must detect in ms if it was touched or not"   what is   ms ,  you need a touch force of 30Kg?
Please explain your application , in order to guide you more appropriately.

Ts

[somewhere]

Hi Trishool !

I will use it in dogsports for contact areas.
With the sensor I will detect if the dog touches the zone (that means ms).
In case of a table the sensor is used also to detect how long the dog is on the table.
The minimum requiered time is 5 seconds and the count starts as soon as the dog touches the sensor immidiatly.

Maybe this describes my project a little bit more clear in few sentences.

regards
somewhere

[somewhere]

Sorry one additional info.

The reason why I ask for the weigth sensitifity is, dogs can have weigth eg. of 2kg but also eg. 28kg and each weight beetween.
Therefore the sensitifity in the range from 0,5kg to 30kg is important not the measurment of weigth.

regards again
somewhere

[bbarney]

I think the touch sensor won't care what the dog weigh's so it's a better way to go plus you can make your touch pads any size you want within reason the bigger the pad the less sensitive heres some links
http://www.touchsensor.com/home.html
http://www.qprox.com/downloads/appnotes.php


this is interesting
http://cs.nyu.edu/~jhan/ledtouch/index.html
and these vibration tab sensors
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=MSP1006-ND

[Trishool]

Hi Trishool !

In case of a table the sensor is used also to detect how long the dog is on the table.
The minimum requiered time is 5 seconds and the count starts as soon as the dog touches the sensor immidiatly.
[/quote ]



Hi Somewhere , See the part you describe 5 seconds is a timing process and maybe it would require some accuracy to announce the winner , for this I would suggest an FSR or Flexiforce sensor low cost but accurate , the Flexiforce sensor is more accurate the 100lb force range would solve the purpose. And for touch sensors  as   bbarney  has already stated you can use that.

BTW what exactuly you mean by touch sensor? , the dogs nose ? or its presence.

TrIsHooL

[somewhere]

First of all thank's for your reply. I will look at the linked pages.

Trishool to your question.
Normally the dog jumps on the table during the race and touch the table with his paws.
But the first paw contact is not done with the dogs full weight.

somewhere

[Ichan]

Hi, some years ago i made a basket ball passing meter, it measures the force of the passed (threw) basket ball when it hit the target. The target made from about 10mm thick 40 x 40 cm pvc board with a load cell behind it, the load cell itself is an assembly of strain gage taken from a cheap bathroom scale (very cheap sources of load cell, they have 4 load cell per unit!).

Regards, Ichan.

Ps: You are right, timing is critical... took me days to solve it.. 

[somewhere]

Hi Ichan,
I checked also the possibility of load cells. I think it's a good idea
but I'm not sure if it works on this big sized area.

I think I've found a solution now. Because of I don't need to know the exact weight I try to
fix it with microswitches and a mechanical solution.
If I know some results I will post it.

Thanks for all your reposts.

somewhere

[Parmin]

To reiterate.

If you want the weigh of the dog, then use the load cell, but I am sure that the weighing will not be done in the ms (milliseconds) it would be more like a few seconds to stabilize. Unless if you want to measure the IMPACT load then it could be done in the milliseconds or even microseconds (used in measuring pressure load on a rifle barrel when the cartridge is ignited).

If you want to know WHEN the dog reach a certain area (eg. finish line) then use a light curtain. Fast enough to measure the speed of a bullet as in chronograph.

If you want to activate something when the dog reach the sensor, you could use Passive infrared on narrow band. Something like the common household PIR but with the lens covered up and left only with a small slit.

[Trishool]

but I'm not sure if it works on this big sized area.

I think I've found a solution now. Because of I don't need to know the exact weight I try to
fix it with microswitches and a mechanical solution.
If I know some results I will post it.

Thanks for all your reposts.

somewhere

somewhere , you can use microswitches , but a more easy according to me would be a spring mass system with leaf contacts (leaf can be a strip of brass bent at an angle say 45degrees), Place a fixed board on the ground suspend another board(thick cardboard/wood) with a aluminium foil mounted on the back side , tie GND to this sheet . Place springs at the all four corners of the bottom board , along with the leafs and now place the top board with foil over it .As soon as the dog will press it a GND contact for the MCU will be generated . I feel this could be the lowest cost solution .

Ts