PIC32MX: Interfacing with Force Sensors from a Scale - Revision history

NickMarchuk at 20:21, 1 March 2010

2010-03-01T20:21:05Z

2010-02-16T18:57:04Z

Overview

2010-02-16T18:51:10Z

Next Steps and Files

2010-02-16T18:41:58Z

Processing Code

2010-02-16T14:57:53Z

Processing Code

2010-02-16T14:56:27Z

Next Steps and Files

2010-02-16T14:46:51Z

Processing Code

2010-02-16T05:30:53Z

Next Steps and Files

2010-02-16T05:30:08Z

Next Steps and Files

2010-02-16T05:21:23Z

Processing Code

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-== Original Assignment ==
-'''Do not erase this section!'''
-Your assignment is to use four analog inputs to continuously read four force sensors taken from a bathroom scale, and to display them on a PC screen as bars whose length corresponds to the force at the sensors.  You will use Processing for the PC data acquisition and graphics.
 == Overview ==

@@ Line 7: / Line 7: @@
 == Overview ==
-A BME Senior Design project group is developing a device to measure the weight shifting ability of a child with Cerebral Palsy. The end goal is develop an interface that will allow the child to visually see on a screen how they are shifting their weight.
+A BME Senior Design project group is developing a device to measure the weight shifting ability of a child with Cerebral Palsy. The end goal is to develop a video game that is controlled by the child shifting their weight. Hopefully this device will allow the children to improve their balance while having fun playing a video game.
 Our portion of the project involves designing the hardware to read the signals from 4 load cells and writing code to read in the load values to a PIC 32 microcontroller which is then sent to a PC via RS232. Additionally we developed an interface for the PC that visually represents the collected data in a useful and intuitive format.

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 One of the global variables, mapping integer "m," determines the sensitivity of the sensors.  Our potentiometers are tuned to output a miniscule positive voltage difference which is amplified by 675.  The resulting value falls within our initial range of 0-m (default: 0-511) which is then mapped to a floating-point number range 0-255.  We found that the default initial range of 0-511 (m = 511) works well for adults standing on the scale.  For adults using their hands to exert force on the scale, the range 0-200 (m = 200) is more suitable.  Thus, as m is decreased, the sensitivity is increased.  This mapping variable can be altered for each individual user, especially cerebral palsy patients, for which this scale is designed.
-==Next Steps and Files==
+==Next Steps==
-'''Next Steps'''
 . Develop a printed circuit board that contains all amplification circuitry, the microcontroller, and tunning circuits. Additionally, redesign the tunning circuit so that it is more robust.
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+==Files==
-'''Downloadable files and links:'''
 The full Processing code can be found [http://hades.mech.northwestern.edu/images/5/54/Processing_lab5.zip here].

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 == Processing Code ==
-'''The Processing portion of our lab involves 4 main sections:'''
+'''The Processing portion of our lab involves 4 visible sections:'''
 . Colorbars, ''colorbars();''

← Older revision		Revision as of 14:57, 16 February 2010
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	'''Screenshots:''' exerting force on the sensors in a circular pattern (left) and exerting force on one sensor at a time (right).		'''Screenshots:''' exerting force on the sensors in a circular pattern (left) and exerting force on one sensor at a time (right).

	[[Image:Circle.jpg \| ~~450px~~]] [[Image:loadon1sensor.jpg \| ~~450px~~]]		[[Image:Circle.jpg \| 500px]] [[Image:loadon1sensor.jpg \| 500px]]

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 . Find a formula(hopefully linear) that equates the voltages seen from the sensors to mass. This can be done by using a few objects whose mass's are known.
 .  Develop a chart that details what the "m" mapping variable value should be for a user's body weight and configure the scale to automatically adjust the m value when a user steps on the scale.
 .  Also, make the colorbars or plot dots change to a certain color and/or have the computer play a sound when a certain mass amplitude value on a sensor has been breached.  This may be useful for cerebral palsy patients that are being trained to maintain balance.

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 . Y-position vs. time ''(not a separate function)''
-continuously plots a dot for the y-position along a time axis.  This plot will be useful to see how much the person shifts his/her weight forward or backwards (dorsoventral shift) over time.  The code for this section is essentially the same as the x-position but edited to show y-position.
+continuously plots a dot for the y-position along a time axis.  This plot will be useful to see how much the person shifts his/her weight forward or backwards (anteroposterior shift) over time.  The code for this section is essentially the same as the x-position but edited to show y-position.
@@ Line 131: / Line 131: @@
 One of the global variables, mapping integer "m," determines the sensitivity of the sensors.  Our potentiometers are tuned to output a miniscule positive voltage difference which is amplified by 675.  The resulting value falls within our initial range of 0-m (default: 0-511) which is then mapped to a floating-point number range 0-255.  We found that the default initial range of 0-511 (m = 511) works well for adults standing on the scale.  For adults using their hands to exert force on the scale, the range 0-200 (m = 200) is more suitable.  Thus, as m is decreased, the sensitivity is increased.  This mapping variable can be altered for each individual user, especially cerebral palsy patients, for which this scale is designed.
 ==Next Steps and Files==

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+==Next Steps and Files==
-'''Potential Future Work:'''
 .  Use at least 3 objects to experimentally obtain amplitude values.  Determine the relationship between sensors (hopefully it's linear!) to compute the actual mass in kilograms and pounds on top of each sensor and extrapolate the full mass between all 4 sensors (measure a user's body weight).
@@ Line 142: / Line 142: @@
 .  Also, make the colorbars or plot dots change to a certain color and/or have the computer play a sound when a certain mass amplitude value on a sensor has been breached.  This may be useful for cerebral palsy patients that are being trained to maintain balance.
-.  Develop a printed circuit board specifically for this scale.
+.  Develop a printed circuit board specifically for this scale which allows for easier tuning.