Ambient light color sensing - Revision history

Lynch at 22:39, 2 March 2008

2008-03-02T22:39:35Z

← Older revision		Revision as of 17:39, 2 March 2008
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	== Original Assignment ==

	The goal of this project is to build a sensor that can detect the color of light produced by an LCD projector (such as the one in the lab). The sensor will consist of three tightly bundled phototransistors (e.g., the OP506B from digikey), each with its own color filter (see, for example, this [[Media:color_filters.pdf\|description of color filters]]). Three analog inputs will read the sensed values and the program will print the RGB (or similar) values to an LCD screen (see, e.g., [[C_Example:_Serial_LCD]] or [[C_Example:_Parallel_Interfacing_with_LCDs]]). The demonstration will show these values changing as you move from one part of the projected image (a simple test pattern consisting of single-color blocks) to another.

	== Overview ==		== Overview ==

BenjaminMurphy: /* Overview */

2008-02-13T22:02:56Z

Overview

← Older revision		Revision as of 17:02, 13 February 2008
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	[[Image:LCDRGB.jpg\|left]]		[[Image:LCDRGB.jpg\|left]]

	Once you have three different phototransistor voltages that are dependent on 3 RGB values, each one can be connected to the PIC via an analog input. While the voltage read may be between 0 and 5, it can be adjusted linearly to a scale from 0 to 255, the range for an RGB value. Each transistor will have a value from 0 to 255, which can then be reconstructed back into a single color on the computer, or can be printed out to an LCD screen.		The sensitivity of the phototransistor depends on the resistance R. Using a larger resistance will allow for an increase in the ability to detect changes in light. Once you have three different phototransistor voltages that are dependent on 3 RGB values, each one can be connected to the PIC via an analog input. While the voltage read may be between 0 and 5, it can be adjusted linearly to a scale from 0 to 255, the range for an RGB value. Each transistor will have a value from 0 to 255, which can then be reconstructed back into a single color on the computer, or can be printed out to an LCD screen.

	The LCD screen is a two-line parallel port screen, model MCC162A4-5. The information for displaying content on the lcd screen can be found here: [[C_Example:_Parallel_Interfacing_with_LCDs]].		The LCD screen is a two-line parallel port screen, model MCC162A4-5. The information for displaying content on the lcd screen can be found here: [[C_Example:_Parallel_Interfacing_with_LCDs]].

BenjaminMurphy: /* Overview */

2008-02-13T21:59:10Z

Overview

← Older revision		Revision as of 16:59, 13 February 2008
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	== Overview ==		== Overview ==

	[[Image:Phototrans.jpg\|right]]		[[Image:Phototrans.jpg\|thumbnail\|right]]

	A phototransistor will alter its emitter current according to the amount of light shone upon its base input. Thus, the current will be at its maximum when the transistor receives the most light, and at a minimum when it receives no light. To translate this current into a voltage measurable by the PIC, the voltage can be probed across a resistor placed in series at the collector or emitter of the phototransistor. This means that maximum voltage (at maximum light exposure) should be approximately equal to the input voltage at the collector, minus the voltage drop across the transistor, and the minimum voltage should be approximately zero.		A phototransistor will alter its emitter current according to the amount of light shone upon its base input. Thus, the current will be at its maximum when the transistor receives the most light, and at a minimum when it receives no light. To translate this current into a voltage measurable by the PIC, the voltage can be probed across a resistor placed in series at the collector or emitter of the phototransistor. This means that maximum voltage (at maximum light exposure) should be approximately equal to the input voltage at the collector, minus the voltage drop across the transistor, and the minimum voltage should be approximately zero.

BenjaminMurphy: /* Overview */

2008-02-13T21:58:50Z

Overview

← Older revision		Revision as of 16:58, 13 February 2008
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	To split the source light into separate colors, color filters must be used to block out other wavelengths of light. A red color filter will allow red light to pass through (650 nm), a cyan filter will allow cyan light to pass through, and a green filter will allow green light to pass through (510 nm). Note that filters may also allow light out of the visible spectrum (for example, Infrared radiation), so be sure to consult the spectral property of the individual filter you intend to use. The spectrum of the green filter can be seen on the right. (Click [http://hades.mech.northwestern.edu/wiki/images/5/50/Color_filters.pdf here] for filter spec sheet).		To split the source light into separate colors, color filters must be used to block out other wavelengths of light. A red color filter will allow red light to pass through (650 nm), a cyan filter will allow cyan light to pass through, and a green filter will allow green light to pass through (510 nm). Note that filters may also allow light out of the visible spectrum (for example, Infrared radiation), so be sure to consult the spectral property of the individual filter you intend to use. The spectrum of the green filter can be seen on the right. (Click [http://hades.mech.northwestern.edu/wiki/images/5/50/Color_filters.pdf here] for filter spec sheet).

	[[Image:Color_filter.JPG\|right]]		[[Image:Color_filter.JPG\|thumbnail\|right]]

	These three filters will split light into Red-Green-Blue (RGB) components, a common quantification of the visible spectrum in PCs. Note that phototransistors may be sensitive to differing wavelengths of light, usually visible light or IR phototransistors- make sure you choose the correct one for your purposes.		These three filters will split light into Red-Green-Blue (RGB) components, a common quantification of the visible spectrum in PCs. Note that phototransistors may be sensitive to differing wavelengths of light, usually visible light or IR phototransistors- make sure you choose the correct one for your purposes.

BenjaminMurphy: /* Overview */

2008-02-13T21:58:28Z

Overview

← Older revision		Revision as of 16:58, 13 February 2008
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	To split the source light into separate colors, color filters must be used to block out other wavelengths of light. A red color filter will allow red light to pass through (650 nm), a cyan filter will allow cyan light to pass through, and a green filter will allow green light to pass through (510 nm). Note that filters may also allow light out of the visible spectrum (for example, Infrared radiation), so be sure to consult the spectral property of the individual filter you intend to use. The spectrum of the green filter can be seen on the right. (Click [http://hades.mech.northwestern.edu/wiki/images/5/50/Color_filters.pdf here] for filter spec sheet).		To split the source light into separate colors, color filters must be used to block out other wavelengths of light. A red color filter will allow red light to pass through (650 nm), a cyan filter will allow cyan light to pass through, and a green filter will allow green light to pass through (510 nm). Note that filters may also allow light out of the visible spectrum (for example, Infrared radiation), so be sure to consult the spectral property of the individual filter you intend to use. The spectrum of the green filter can be seen on the right. (Click [http://hades.mech.northwestern.edu/wiki/images/5/50/Color_filters.pdf here] for filter spec sheet).

	[[Image:Color_filter.~~jpg~~\|right]]		[[Image:Color_filter.JPG\|right]]

	These three filters will split light into Red-Green-Blue (RGB) components, a common quantification of the visible spectrum in PCs. Note that phototransistors may be sensitive to differing wavelengths of light, usually visible light or IR phototransistors- make sure you choose the correct one for your purposes.		These three filters will split light into Red-Green-Blue (RGB) components, a common quantification of the visible spectrum in PCs. Note that phototransistors may be sensitive to differing wavelengths of light, usually visible light or IR phototransistors- make sure you choose the correct one for your purposes.

BenjaminMurphy: /* Overview */

2008-02-13T21:58:00Z

Overview

← Older revision		Revision as of 16:58, 13 February 2008
Line 11:		Line 11:
	To split the source light into separate colors, color filters must be used to block out other wavelengths of light. A red color filter will allow red light to pass through (650 nm), a cyan filter will allow cyan light to pass through, and a green filter will allow green light to pass through (510 nm). Note that filters may also allow light out of the visible spectrum (for example, Infrared radiation), so be sure to consult the spectral property of the individual filter you intend to use. The spectrum of the green filter can be seen on the right. (Click [http://hades.mech.northwestern.edu/wiki/images/5/50/Color_filters.pdf here] for filter spec sheet).		To split the source light into separate colors, color filters must be used to block out other wavelengths of light. A red color filter will allow red light to pass through (650 nm), a cyan filter will allow cyan light to pass through, and a green filter will allow green light to pass through (510 nm). Note that filters may also allow light out of the visible spectrum (for example, Infrared radiation), so be sure to consult the spectral property of the individual filter you intend to use. The spectrum of the green filter can be seen on the right. (Click [http://hades.mech.northwestern.edu/wiki/images/5/50/Color_filters.pdf here] for filter spec sheet).

	[[Image:Color_filter.jpg\|~~thumbnail\|left~~]]		[[Image:Color_filter.jpg\|right]]

	These three filters will split light into Red-Green-Blue (RGB) components, a common quantification of the visible spectrum in PCs. Note that phototransistors may be sensitive to differing wavelengths of light, usually visible light or IR phototransistors- make sure you choose the correct one for your purposes.		These three filters will split light into Red-Green-Blue (RGB) components, a common quantification of the visible spectrum in PCs. Note that phototransistors may be sensitive to differing wavelengths of light, usually visible light or IR phototransistors- make sure you choose the correct one for your purposes.

BenjaminMurphy: /* Overview */

2008-02-13T21:57:10Z

Overview

← Older revision		Revision as of 16:57, 13 February 2008
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	A phototransistor will alter its emitter current according to the amount of light shone upon its base input. Thus, the current will be at its maximum when the transistor receives the most light, and at a minimum when it receives no light. To translate this current into a voltage measurable by the PIC, the voltage can be probed across a resistor placed in series at the collector or emitter of the phototransistor. This means that maximum voltage (at maximum light exposure) should be approximately equal to the input voltage at the collector, minus the voltage drop across the transistor, and the minimum voltage should be approximately zero.		A phototransistor will alter its emitter current according to the amount of light shone upon its base input. Thus, the current will be at its maximum when the transistor receives the most light, and at a minimum when it receives no light. To translate this current into a voltage measurable by the PIC, the voltage can be probed across a resistor placed in series at the collector or emitter of the phototransistor. This means that maximum voltage (at maximum light exposure) should be approximately equal to the input voltage at the collector, minus the voltage drop across the transistor, and the minimum voltage should be approximately zero.

	To split the source light into separate colors, color filters must be used to block out other wavelengths of light. A red color filter will allow red light to pass through (650 nm), a cyan filter will allow cyan light to pass through, and a green filter will allow green light to pass through (510 nm). Note that filters may also allow light out of the visible spectrum (for example, Infrared radiation), so be sure to consult the spectral property of the individual filter you intend to use. The spectrum of the green filter can be seen on the right. (Click here for filter spec sheet) ~~These three filters will split light into Red-Green-Blue (RGB) components, a common quantification of the visible spectrum in PCs~~. ~~Note that phototransistors may be sensitive to differing wavelengths of light, usually visible light or IR phototransistors- make sure you choose the correct one for your purposes.~~		To split the source light into separate colors, color filters must be used to block out other wavelengths of light. A red color filter will allow red light to pass through (650 nm), a cyan filter will allow cyan light to pass through, and a green filter will allow green light to pass through (510 nm). Note that filters may also allow light out of the visible spectrum (for example, Infrared radiation), so be sure to consult the spectral property of the individual filter you intend to use. The spectrum of the green filter can be seen on the right. (Click [http://hades.mech.northwestern.edu/wiki/images/5/50/Color_filters.pdf here] for filter spec sheet).

			[[Image:Color_filter.jpg\|thumbnail\|left]]

			These three filters will split light into Red-Green-Blue (RGB) components, a common quantification of the visible spectrum in PCs. Note that phototransistors may be sensitive to differing wavelengths of light, usually visible light or IR phototransistors- make sure you choose the correct one for your purposes.

BenjaminMurphy: /* Overview */

2008-02-13T21:55:18Z

Overview

← Older revision		Revision as of 16:55, 13 February 2008
Line 9:		Line 9:
	A phototransistor will alter its emitter current according to the amount of light shone upon its base input. Thus, the current will be at its maximum when the transistor receives the most light, and at a minimum when it receives no light. To translate this current into a voltage measurable by the PIC, the voltage can be probed across a resistor placed in series at the collector or emitter of the phototransistor. This means that maximum voltage (at maximum light exposure) should be approximately equal to the input voltage at the collector, minus the voltage drop across the transistor, and the minimum voltage should be approximately zero.		A phototransistor will alter its emitter current according to the amount of light shone upon its base input. Thus, the current will be at its maximum when the transistor receives the most light, and at a minimum when it receives no light. To translate this current into a voltage measurable by the PIC, the voltage can be probed across a resistor placed in series at the collector or emitter of the phototransistor. This means that maximum voltage (at maximum light exposure) should be approximately equal to the input voltage at the collector, minus the voltage drop across the transistor, and the minimum voltage should be approximately zero.

	To split the source light into separate colors, color filters must be used to block out other wavelengths of light. A red color filter will ~~only~~ allow red light to pass through (650 nm), a cyan filter will ~~only~~ allow cyan light to pass through, and a green filter will ~~only~~ allow green light to pass through (510 nm). These three filters will split light into Red-Green-Blue (RGB) components, a common quantification of the visible spectrum in PCs. Note that phototransistors may be sensitive to differing wavelengths of light, usually visible light or IR phototransistors- make sure you choose the correct one for your purposes.		To split the source light into separate colors, color filters must be used to block out other wavelengths of light. A red color filter will allow red light to pass through (650 nm), a cyan filter will allow cyan light to pass through, and a green filter will allow green light to pass through (510 nm). Note that filters may also allow light out of the visible spectrum (for example, Infrared radiation), so be sure to consult the spectral property of the individual filter you intend to use. The spectrum of the green filter can be seen on the right. (Click here for filter spec sheet) These three filters will split light into Red-Green-Blue (RGB) components, a common quantification of the visible spectrum in PCs. Note that phototransistors may be sensitive to differing wavelengths of light, usually visible light or IR phototransistors- make sure you choose the correct one for your purposes.

Lynch: /* Overview */

2008-02-09T21:55:59Z

Overview

← Older revision		Revision as of 16:55, 9 February 2008
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	[[Image:Phototrans.jpg\|right]]		[[Image:Phototrans.jpg\|right]]

	A phototransistor will alter its emitter current according to the amount of light shone upon its base input. Thus, the current will be at its maximum when the transistor receives the most light, and at a minimum when it receives no light. To translate this current into a voltage ~~measureable~~ by the PIC, the voltage can be probed across a resistor placed in series ~~following~~ the ~~emitter~~ ~~portion~~ of the phototransistor. This means that maximum voltage (at maximum light exposure) should be approximately equal to the input voltage at the collector, minus the voltage drop across the transistor, and the minimum voltage should be approximately zero.		A phototransistor will alter its emitter current according to the amount of light shone upon its base input. Thus, the current will be at its maximum when the transistor receives the most light, and at a minimum when it receives no light. To translate this current into a voltage measurable by the PIC, the voltage can be probed across a resistor placed in series at the collector or emitter of the phototransistor. This means that maximum voltage (at maximum light exposure) should be approximately equal to the input voltage at the collector, minus the voltage drop across the transistor, and the minimum voltage should be approximately zero.

	To split the source light into separate colors, color filters must be used to block out other wavelengths of light. A red color filter will only allow red light to pass through (650 nm), a cyan filter will only allow cyan light to pass through, and a green filter will only allow green light to pass through (510 nm). These three filters will split light into Red-Green-Blue (RGB) components, a common quantification of the visible spectrum in PCs. Note that phototransistors may be sensitive to differing wavelengths of light, usually visible light or IR phototransistors- make sure you choose the correct one for your purposes.		To split the source light into separate colors, color filters must be used to block out other wavelengths of light. A red color filter will only allow red light to pass through (650 nm), a cyan filter will only allow cyan light to pass through, and a green filter will only allow green light to pass through (510 nm). These three filters will split light into Red-Green-Blue (RGB) components, a common quantification of the visible spectrum in PCs. Note that phototransistors may be sensitive to differing wavelengths of light, usually visible light or IR phototransistors- make sure you choose the correct one for your purposes.

MichaelKryger: /* Circuit */

2008-02-08T05:05:57Z

Circuit

← Older revision		Revision as of 00:05, 8 February 2008
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	[[Image:Photo_circuit.jpg]]		[[Image:Photo_circuit.jpg]]

	~~All~~ ~~resistors are~~ 100 kOhm. ~~The potentiometer~~ has a ~~maximum~~ value of 10 kOhms.		R = 100 kOhm. Rp has a max value of 10 kOhms.

	Note that if the positions of the phototransistors are swapped with that of the resistors, the input signs will be reversed.		Note that if the positions of the phototransistors are swapped with that of the resistors, the input signs will be reversed.