project weight
How can help me? i want to start with my basic stamp discovery kit. for a (school) robotic project i want to monitor the weight a cup of water while water is leaking. at a certain point an alarm (sound or led lights up)should go off. the weight of the cup and water is about 400 grams; the alarm should go at e.g. 30 gram.·i want to·program the uC Basic stamp and put it in a small robot stand-alone.·the signal comes from a flexiforce demokit sensor;·energy from a small battery
who can help me with circuit suggestions and maybe a small Basic program?
thanks!
sofos, Belgium
who can help me with circuit suggestions and maybe a small Basic program?
thanks!
sofos, Belgium
Comments
Based on how I'm reading the flexiforce data sheet, I don't think you will be able to get either the low end range, nor the accuracy that you may need for your project. I certainly stand to be corrected, however.
A better bet might be to go with a load cell (wheatstone bridge principle):
http://en.wikipedia.org/wiki/Wheatstone_bridge
Regards,
Bruce Bates
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You might also want to look at the "Applied Sensors" manual for measuring liquid levels.
Both manuals can be downloaded from the Parallax website.
Oh sure. What you want to do it quite doable. I am by no means a load cell "expert", but here's how I would approach it:
1. Find an appropriate load cell which meets your particular needs. This will include force range, physical size and accuracy.
2. Find an appropriate A/D chip which is DESIGNED for load cell applications. Often these contain an amplifier and/or an exciter circuit if one is needed. A good place to look is Linear Technologies. You might even be able to get them to part with a sample. Again, make sure the load cell A/D chip meets the specifications and accuracy you require.
3. Hook it up, test it out, calibrate it if necessary, and you should be pretty much good to go.
Best of luck with your project.
Regards,
Bruce Bates
Post Edited (Bruce Bates) : 8/24/2006 3:46:51 PM GMT
Since the flexforce measures 0 to 100 lbs in 0 to 4.5V your 30 grams trigger is just way to small to measure with it.
How about a balance system similar to the wheatstone idea
Set up a balance platform scale, put 30 grams on one side and your cup for the water on the other side as the water leaks out to the point where both sides are equal weight the beam will be parallel and continue to rotate until the beam bottoms out. Connect a simple on off switch to the beam so that when it tipspast center yoiu know the cup side is less than 30 grams. (add the cup weight as well to the measurement side)
cup
30gms
........... /\..................... trigger switch when this side drops past centerline.
The other sensor you need is to measure the flow of the water you said.
Since the state fair just started, I am thinking about the ferris wheel...
Use a circle cut from plastic maby 2" diameter, put slots in edges maby 20 around the diameter, inset small plastic squares to make a mini waterwheel
put that under the flow of water comming from the cup, on the water wheel put a on off sensor to measure its rotation, if it's not rotating there is no water flow.
If it's just drops of water use an ir sensor and a black center (hubcap) with holes in it, a light on one side and count the pulses of light to see if it's spinning.
Course there are a million other ways to do it as well.
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Think outside the BOX!
Post Edited (metron9) : 8/24/2006 3:36:36 PM GMT
my idea was and with your suggestions : a wheatstone bridge/load cell -> analog signal -> A/D convertor-> digital signal -> stamp kit -> Basic program for setpoint and monitoring teh weight -> stamp upload -> stand alone
this nis teh beginning: now i have to consider teh components and programming. maybe you can help me with some circuit ideas?
i hope i am not asking too much.
thanks again
sofos
For my application: can i built this system on the parrallax Basic stamp kit? and/ or can somebody advise me which uC to use for programming the setpoint (cerian weight) and monitoring the amount water in the cup·(weight monitoring over time) and the other parts. i am·not very familiar with this stuff. thanks again. sofos
I use BS2 with the AD7730 in weigh scale application like liquid filler and·checkweigher.I use keypad for programming setpoints.
Look at my first project:
http://www.parallax.com/html_pages/resources/custapps/app_paint.asp
Go to forum search and search for AD7730.
Mohamed Refky
·
BS2 code reads the 16 bit word and converts it to weight so you will program
a setpoint at certain weight not resistance of the load cell.
Here is example codes of writing and reading of registers:
ADdata···· ·var·word· 'variable to hold 16 bit result.
DATAin······con·2····· 'AD data input pin.
DATAout··· con·3····· 'AD data output pin.
SCKL········ con·4···· ·'clock to AD.
RDY··········con·5····· 'RDY input .
input 5
Initial:
SHIFTOUT DATAin,SCLK,MSBFIRST,[noparse][[/noparse]$FFFF\16,$FFFF\16]·'write 32 ones will reset the AD7730 to the default state.
SHIFTOUT DATAin,SCLK,MSBFIRST,[noparse][[/noparse]$02]··'write to communication register setting next operation as write to mode register.
SHIFTOUT DATAin,SCLK,MSBFIRST,[noparse][[/noparse]$3080\16]·'write to mode register starting continuous conversion for 10mV input range,unipolar,16 bit data word and 5V reference.
SHIFTOUT DATAin,SCLK,MSBFIRST,[noparse][[/noparse]$21]··'write to communication register setting next operation as continuous read from data· register.
low 2········ ' set DIN line low to insure part is not reset while in continuous reade mode.
ReadData:
waitRDY:
··· IF RDY = 1 THEN waitRDY···'wait for RDY to go low to indicate output update.
··· SHIFTIN DATAout,SCLK,MSBPOST,[noparse][[/noparse]ADdata\16]·'read conversion result from data register.
DEBUG DEC ADdata,cr····'display data in decimal.
pause 500················· ·'wait 0.5 second between reading.
GOTO ReadData
thanks again for your reply if possible, sofos
http://www.revere.nl/Index/indexp.htm
thanks!
Since the spring will contract as it gets lighter, you can measure the position by using a variety of methods:
electro-mechanical, potentiometers, light, or sound.
You could use ultrasonic distance to measure the bottom of the cup, you could use a sliding [noparse][[/noparse]linear motion] potentiomer to measure the distance, paired leds and sensors, or you could set up a series of electical contacts that indicate exact possition.
The BasicStamp will generally limit you to only 16 electrical contacts.· If that is not enough resolution, I suspect you can use logic chips to gain a higher resolution.
This project is really about reliable calibration and selecting a system that will allow that.
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