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Hi,
I'm trying to build a system for storing flour, cofeee etc. and to separate electronically a small amount of it. For example, if I want just 1g of cofee, the system will give me it.

Anyone has an idea?

I tought about using something like a water level sensor, so I could make a relation between weight and percentage of pot filled, but it doesn't seem good, since I wouldn't have a lot of precision and it is kind difficult to create a system to open and close fastly the larger container (so I could open it, wait the the required amount falling and close it).

Thanks
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you can use force sensitive resistors. force sensitive resistors are flat like a piece of paper and you just place weight on them and measure it with a analogRead()
https://www.sparkfun.com/products/9376     this one is cheap and not as accurate
https://www.sparkfun.com/products/8685    this one is more expensive but is very accurate. I have tried this sensor and recommend it.
« Last Edit: December 28, 2012, 04:33:51 pm by arduinopi » Logged

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Nice.
The main problem is how to build this system to measure automatically, because the machine should separate the required amount (using a force sensitive sensor) without any waste and without putting in and putting out several times.
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Nice.
The main problem is how to build this system to measure automatically, because the machine should separate the required amount (using a force sensitive sensor) without any waste and without putting in and putting out several times.

see if u can do this with non-liquids.
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&ved=0CDgQtwIwAQ&url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3D9rSgAu4qYaU&ei=pRveUNOhNe-L4gSnu4HADg&usg=AFQjCNFiCQzvaR4U50i-t0lfH22TA4B21Q&bvm=bv.1355534169,d.Yms
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The force sensitive resistor can be programed with the arduino for autonomy. you need something mechanical to release the coffee/flour. you could get a funnel with a very small hole put a servo to close the hole off when not in use. you would need the hole to be so small the substance would come out only when shaken. you could then put a vibration motor on the funnel to shake it out into a container on top of a force sensitive resistor.
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As an alternative to the shaker, you could use a pintle style valve - basically a hole big enough for the media to pass through, with a cylindrical plug that is big enough to exactly fill the hole which is pulled back inside the reservoir to open, and pushed back to fill the hole to stop the flow. This style of valve would be inherently self-clearing and resistant to jamming/blocking. The size of the opening determines the flow rate, and you'd want to make it small enough to start/stop the flow within the resolution that you're trying to measure, and significantly larger than the granules that need to pass through it.
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PeterH, do you know if there is any eletronic pintle style valve? I only found those old ones, mechanically controlled.

This kind of valve solve the problem to "close the funnel". I would need to create a valve to open and close it. Maybe I should attach a vibration motor, depending on the geometry and the experimental results.

Sergegsx, that is exactly what I want to build but for non-liquids and small quantities.
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Look into bullet reloading equipment for inspiration -- the powder measuring part. A "trickler" is a horizontal, vibrating tube tee'd from a funnel for very small rates of feeding. Shotgun shell reloading equipment uses a rectangular bar with a hole in it that is pushed back and forth to measure a set amount of powder/shot; the reciprocating motion would be pretty easy with an RC servo and has the advantage of sealing your container when stopped. If you need a lot of volume to move then you'd have to go with some type of auger system. Perhaps a compression spring could be used for the auger.
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The only ones I know of are used for fluids and not suitable for this application, but I would have thought the basic design was suitable for what you're trying to do. I'd envisage a conical reservoir with a small opening at the bottom, with a cylindrical plug filling the hole; a servo would lift the plug up inside the reservoir to let the material out.
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