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Topic: Weight sensor (Read 144 times) previous topic - next topic

sm535

This will be my first serious Arduino project. Greatly appreciate your guidance on the question I have.

I would like to detect if someone is sitting on a chair. Preferably, I need a binary decision directly from the sensor. If not, I know the range of weight I need to detect and I can detect the analog weight (or equivalent) and can deduce the binary decision.

My question is what should I use as a weight sensor? I can think of three possibilities:

1. Use FlexiForce: http://www.tekscan.com/store/flexiforce-sensors.html
    Way too costly even though it sounds like it does exactly what I need. Is there a low cost alternative?
2. Pressure sensors (such as, Sensore pressione MD-PS002)
    Elsewhere in this forum, I read a lot of associated work needed to make it work. Is there a similarly priced (=cheap) item that simply give the binary 1 or 0 when it is sat upon?
3. Piezo sensors
   I am not sure if this is a solution for the given problem. It might be too sensitive etc. But I am open to it if it works.

For my application it is important that the sensing surface be flat and not something like: http://www.omega.com/ppt/pptsc_lg.asp?ref=PXCPC&Nav=

Thanks very much in advance for your help.

Peter_n

#1
Jul 19, 2014, 07:14 pm Last Edit: Jul 19, 2014, 07:16 pm by Peter_n Reason: 1
I think there is just one good solution: force sensitive resistors
Like this one: https://www.sparkfun.com/products/9375
I would use more than one, perhaps three in 'strategic' locations.

They have a maximum of 10kg. More weight will not damage it, but I don't know the break force.

You have thought well about it, but using a pressure sensor that measures the air pressure is not possible in this situation.
A piezo element would detect the sitting down or rising up. You would not be able to detect if someone is sitting down at that moment.

There are other options:

  • Measure the temperature, if it is higher than room temperature, someone might be sitting on the chair.

  • Using a strain gauge. Glue a strain gauge to the metal of the chair in a smart location. The (extremely small) bending of the metal can be detected. You might even measure the weight to determine if the dog has jumped on the chair.

  • Capacitive Library. There is a capacitive library for the Arduino. With a metal foil, you can detect a person sitting on the chair. It is not very reliable, but worth testing and very cheap.


I'm sure others can think of more options.
Everything is binary, even life itself. It consists of only two things: the things that matter and the rest.

sm535

@Peter_n: 

Thanks very much.

Yes, I had to put a '-barometric -air' in my search of pressure sensors to avoid getting results for air pressure sensors.

I am also leaning towards force sensitive resistors. The cost is a bit on the higher side at this moment. However, your suggestions of stress and capacitive sensors are good ones. I will do some more research on them. 

I look forward to more suggestions as well.

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