Sensing optical tape - Revision history

EricN at 18:05, 4 December 2008

2008-12-04T18:05:47Z

← Older revision		Revision as of 13:05, 4 December 2008
Line 57:		Line 57:

	(add circuits for comparator/trimpot, Schmidt trigger, and photodiode amplifier)		(add circuits for comparator/trimpot, Schmidt trigger, and photodiode amplifier)

			'''Reflective Tape'''

			Retroreflective tape comes in many varieties and colors. Retroreflective tape utilizes prism crystals imbedded within a resin matrix which internally reflect light such that it is reflected back in the direction from which it arrived. This makes the tape highly reflective, provided that the observer (or sensor) is closely located with the source of light.

			Quality retroreflective tapes can be obtained from manufacturers such as 3M, but less expensive versions can be obtained through sporting good stores, where they are used as reflective strips for nighttime activities. Common applications of such tapes include vehicle markings, emergency floatation device markings, and motion analysis markers.

LIMS at 20:16, 27 December 2006

2006-12-27T20:16:56Z

← Older revision		Revision as of 15:16, 27 December 2006
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	The QRB1114 optoreflector is popular and is discussed on the [[Optoreflector\|Optoreflector wiki page]]. It consists of an IRED and an IR phototransistor, exactly as discussed here, but together in one package, thus, conveniently pre-aimed. The Emitter and Receiver cones overlap best when a target is at a distance of 0.15 inches. Its sensitivity falls sharply beyond that distance. If you can make do with that distance (or somewhat more) it is very convenient. If you want to specify your own optical geometry, use discrete components.		The QRB1114 optoreflector is popular and is discussed on the [[Optoreflector\|Optoreflector wiki page]]. It consists of an IRED and an IR phototransistor, exactly as discussed here, but together in one package, thus, conveniently pre-aimed. The Emitter and Receiver cones overlap best when a target is at a distance of 0.15 inches. Its sensitivity falls sharply beyond that distance. If you can make do with that distance (or somewhat more) it is very convenient. If you want to specify your own optical geometry, use discrete components.

			'''Tuning'''
⚫	Using a digital input line to tune up your sensing resistor value will be frustrating. Instead, monitor the voltage across your sensing resistor with a digital voltmeter (DVM) or oscilloscope, as you adjust your optical geometry and sensing resistor vale.


		⚫	Using a digital input line on a microcontroller to tune up your sensing resistor value will be frustrating. Instead, monitor the voltage across your sensing resistor with a digital voltmeter (DVM) or oscilloscope, as you adjust your optical geometry and sensing resistor vale.

	(add circuits for comparator/trimpot, Schmidt trigger, and photodiode amplifier)		(add circuits for comparator/trimpot, Schmidt trigger, and photodiode amplifier)

LIMS at 20:15, 27 December 2006

2006-12-27T20:15:09Z

← Older revision		Revision as of 15:15, 27 December 2006
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	If you need to amplify your light signal, or compare it to an adjustable threshold, consider a photodiode amplifier or a comparator such as LM311.		If you need to amplify your light signal, or compare it to an adjustable threshold, consider a photodiode amplifier or a comparator such as LM311.

	The longer lead is the anode. In the second circuit it is cathode up, anode ~~down~~.		The longer lead is the anode. In the second circuit it is cathode top, anode bottom.

	'''Using phototransistors'''		'''Using phototransistors'''
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	The light sensitivity of this phototransistor circuit is probably similar to the photodiode circuit, but its output impedance is 100x less.		The light sensitivity of this phototransistor circuit is probably similar to the photodiode circuit, but its output impedance is 100x less.

	The longer lead is the Emitter. In the third circuit it is Collector up, Emitter ~~down~~.		The longer lead is the Emitter. In the third circuit it is Collector top, Emitter bottom.

	'''Some favorite Emitters and Receivers'''		'''Some favorite Emitters and Receivers'''

LIMS at 20:13, 27 December 2006

2006-12-27T20:13:20Z

← Older revision		Revision as of 15:13, 27 December 2006
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	Photodiodes will conduct like ordinary diodes in the forward direction, so we don't use them that way. The trick is, they conduct backwards when exposed to light: one electron sneaks through for each photon, more or less. So we use them biased in reverse as shown in the second diagram.		Photodiodes will conduct like ordinary diodes in the forward direction, so we don't use them that way. The trick is, they conduct backwards when exposed to light: one electron sneaks through for each photon, more or less. So we use them biased in reverse as shown in the second diagram.

	~~Refering~~ to the second circuit, the photocurrent passes through the sensing resistor, here 1 megohm, so each 1uA of photocurrent results in an output voltage of 1v, up to 5v but no more. If you use a larger sensing resistor, you will get a greater sensitivity. 1M is a lot however: think about the input impedance of whatever you are going to test with or connect this to. Digital voltmeters (DVM) and oscilloscopes usually have an input impedance of 10M, so that's OK. What is the impedance of an input line on a PIC chip or Basic Stamp?		Referring to the second circuit, the photocurrent passes through the sensing resistor, here 1 megohm, so each 1uA of photocurrent results in an output voltage of 1v, up to 5v but no more. If you use a larger sensing resistor, you will get a greater sensitivity. 1M is a lot however: think about the input impedance of whatever you are going to test with or connect this to. Digital voltmeters (DVM) and oscilloscopes usually have an input impedance of 10M, so that's OK. What is the impedance of an input line on a PIC chip or Basic Stamp?

	If you need to amplify your light signal, or compare it to an adjustable threshold, consider a photodiode amplifier or a comparator such as LM311.		If you need to amplify your light signal, or compare it to an adjustable threshold, consider a photodiode amplifier or a comparator such as LM311.
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	Phototransistors will operate like ordinary transistors (here, an NPN transistor) but most do not give you access to the Base. You can see it but you can't touch it. Light falling on the Base acts like a current into the Base. The phototransistor conducts, from Collector to Emitter, a current which is the transistor gain (hfe) times the Base (photo)current. Anyway, it conducts.		Phototransistors will operate like ordinary transistors (here, an NPN transistor) but most do not give you access to the Base. You can see it but you can't touch it. Light falling on the Base acts like a current into the Base. The phototransistor conducts, from Collector to Emitter, a current which is the transistor gain (hfe) times the Base (photo)current. Anyway, it conducts.

	~~Refering~~ to the third circuit, the Collector-Emitter current passes through the sensing resistor, here 10Kohm, so each 0.1mA of current results in an output voltage of 1v, up to almost 5v but no more.		Referring to the third circuit, the Collector-Emitter current passes through the sensing resistor, here 10Kohm, so each 0.1mA of current results in an output voltage of 1v, up to almost 5v but no more.

	The light sensitivity of this phototransistor circuit is probably similar to the photodiode circuit, but its output impedance is 100x less.		The light sensitivity of this phototransistor circuit is probably similar to the photodiode circuit, but its output impedance is 100x less.
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	In infrared (IR), I have used the QED123 IRED (clear pink package) at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The LTR-4206E (IR transparent black package) phototransistor passed about 300uA at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees). [[image:iririr.jpg\|right]]		In infrared (IR), I have used the QED123 IRED (clear pink package) at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The LTR-4206E (IR transparent black package) phototransistor passed about 300uA at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees). [[image:iririr.jpg\|right]]

	The QRB1114 optoreflector is popular and is ~~dicussed~~ on the [[Optoreflector\|Optoreflector wiki page]]. It consists of an IRED and an IR phototransistor, exactly as ~~dicsussed~~ here, but together in one package, thus, conveniently pre-aimed. The Emitter and Receiver cones overlap best when a target is at a distance of 0.15 inches. Its sensitivity falls sharply beyond that distance. If you can make do with that distance (or somewhat more) it is very convenient. If you want to specify your own optical geometry, use discrete components.		The QRB1114 optoreflector is popular and is discussed on the [[Optoreflector\|Optoreflector wiki page]]. It consists of an IRED and an IR phototransistor, exactly as discussed here, but together in one package, thus, conveniently pre-aimed. The Emitter and Receiver cones overlap best when a target is at a distance of 0.15 inches. Its sensitivity falls sharply beyond that distance. If you can make do with that distance (or somewhat more) it is very convenient. If you want to specify your own optical geometry, use discrete components.

	Using a digital input line to tune up your sensing resistor value will be frustrating. Instead, monitor the voltage across your sensing resistor with a digital voltmeter (DVM) or oscilloscope, as you adjust your optical geometry and sensing resistor vale.		Using a digital input line to tune up your sensing resistor value will be frustrating. Instead, monitor the voltage across your sensing resistor with a digital voltmeter (DVM) or oscilloscope, as you adjust your optical geometry and sensing resistor vale.


	(add circuits for comparator/trimpot, ~~schmidt~~ trigger, and photodiode amplifier)		(add circuits for comparator/trimpot, Schmidt trigger, and photodiode amplifier)

LIMS at 20:08, 27 December 2006

2006-12-27T20:08:08Z

← Older revision		Revision as of 15:08, 27 December 2006
Line 48:		Line 48:
	In visible light (red), I have used the SLI-580UT3F LED (clear package)at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The PDB-C134 (clear package) photodiode passed about 1.5uA photocurrent at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees).		In visible light (red), I have used the SLI-580UT3F LED (clear package)at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The PDB-C134 (clear package) photodiode passed about 1.5uA photocurrent at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees).

	In infrared (IR), I have used the QED123 IRED (clear pink package) at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The LTR-4206E (IR transparent black package) phototransistor passed about 300uA at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees). [[image:ir.jpg\|right]]		In infrared (IR), I have used the QED123 IRED (clear pink package) at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The LTR-4206E (IR transparent black package) phototransistor passed about 300uA at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees). [[image:iririr.jpg\|right]]

	The QRB1114 optoreflector is popular and is dicussed on the [[Optoreflector\|Optoreflector wiki page]]. It consists of an IRED and an IR phototransistor, exactly as dicsussed here, but together in one package, thus, conveniently pre-aimed. The Emitter and Receiver cones overlap best when a target is at a distance of 0.15 inches. Its sensitivity falls sharply beyond that distance. If you can make do with that distance (or somewhat more) it is very convenient. If you want to specify your own optical geometry, use discrete components.		The QRB1114 optoreflector is popular and is dicussed on the [[Optoreflector\|Optoreflector wiki page]]. It consists of an IRED and an IR phototransistor, exactly as dicsussed here, but together in one package, thus, conveniently pre-aimed. The Emitter and Receiver cones overlap best when a target is at a distance of 0.15 inches. Its sensitivity falls sharply beyond that distance. If you can make do with that distance (or somewhat more) it is very convenient. If you want to specify your own optical geometry, use discrete components.

LIMS at 20:07, 27 December 2006

2006-12-27T20:07:35Z

← Older revision		Revision as of 15:07, 27 December 2006
Line 48:		Line 48:
	In visible light (red), I have used the SLI-580UT3F LED (clear package)at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The PDB-C134 (clear package) photodiode passed about 1.5uA photocurrent at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees).		In visible light (red), I have used the SLI-580UT3F LED (clear package)at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The PDB-C134 (clear package) photodiode passed about 1.5uA photocurrent at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees).

	In infrared (IR), I have used the QED123 IRED (clear pink package) at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The LTR-4206E (IR transparent black package) phototransistor passed about 300uA at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees).		In infrared (IR), I have used the QED123 IRED (clear pink package) at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The LTR-4206E (IR transparent black package) phototransistor passed about 300uA at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees). [[image:ir.jpg\|right]]

	The QRB1114 optoreflector is popular and is dicussed on the [[Optoreflector\|Optoreflector wiki page]]. It consists of an IRED and an IR phototransistor, exactly as dicsussed here, but together in one package, thus, conveniently pre-aimed. The Emitter and Receiver cones overlap best when a target is at a distance of 0.15 inches. Its sensitivity falls sharply beyond that distance. If you can make do with that distance (or somewhat more) it is very convenient. If you want to specify your own optical geometry, use discrete components.		The QRB1114 optoreflector is popular and is dicussed on the [[Optoreflector\|Optoreflector wiki page]]. It consists of an IRED and an IR phototransistor, exactly as dicsussed here, but together in one package, thus, conveniently pre-aimed. The Emitter and Receiver cones overlap best when a target is at a distance of 0.15 inches. Its sensitivity falls sharply beyond that distance. If you can make do with that distance (or somewhat more) it is very convenient. If you want to specify your own optical geometry, use discrete components.

LIMS at 19:57, 27 December 2006

2006-12-27T19:57:20Z

← Older revision		Revision as of 14:57, 27 December 2006
Line 50:		Line 50:
	In infrared (IR), I have used the QED123 IRED (clear pink package) at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The LTR-4206E (IR transparent black package) phototransistor passed about 300uA at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees).		In infrared (IR), I have used the QED123 IRED (clear pink package) at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The LTR-4206E (IR transparent black package) phototransistor passed about 300uA at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees).

	The QRB1114 optoreflector is popular and is dicussed on the [[Optoreflector wiki page~~\|Optoreflector~~]. It consists of an IRED and an IR phototransistor, exactly as dicsussed here, but together in one package, thus, conveniently pre-aimed. The Emitter and Receiver cones overlap best when a target is at a distance of 0.15 inches. Its sensitivity falls sharply beyond that distance. If you can make do with that distance (or somewhat more) it is very convenient. If you want to specify your own optical geometry, use discrete components.		The QRB1114 optoreflector is popular and is dicussed on the [[Optoreflector\|Optoreflector wiki page]]. It consists of an IRED and an IR phototransistor, exactly as dicsussed here, but together in one package, thus, conveniently pre-aimed. The Emitter and Receiver cones overlap best when a target is at a distance of 0.15 inches. Its sensitivity falls sharply beyond that distance. If you can make do with that distance (or somewhat more) it is very convenient. If you want to specify your own optical geometry, use discrete components.

	Using a digital input line to tune up your sensing resistor value will be frustrating. Instead, monitor the voltage across your sensing resistor with a digital voltmeter (DVM) or oscilloscope, as you adjust your optical geometry and sensing resistor vale.		Using a digital input line to tune up your sensing resistor value will be frustrating. Instead, monitor the voltage across your sensing resistor with a digital voltmeter (DVM) or oscilloscope, as you adjust your optical geometry and sensing resistor vale.

LIMS at 19:56, 27 December 2006

2006-12-27T19:56:02Z

← Older revision		Revision as of 14:56, 27 December 2006
Line 50:		Line 50:
	In infrared (IR), I have used the QED123 IRED (clear pink package) at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The LTR-4206E (IR transparent black package) phototransistor passed about 300uA at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees).		In infrared (IR), I have used the QED123 IRED (clear pink package) at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The LTR-4206E (IR transparent black package) phototransistor passed about 300uA at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees).

			The QRB1114 optoreflector is popular and is dicussed on the [[Optoreflector wiki page\|Optoreflector]. It consists of an IRED and an IR phototransistor, exactly as dicsussed here, but together in one package, thus, conveniently pre-aimed. The Emitter and Receiver cones overlap best when a target is at a distance of 0.15 inches. Its sensitivity falls sharply beyond that distance. If you can make do with that distance (or somewhat more) it is very convenient. If you want to specify your own optical geometry, use discrete components.
	The

	Using a digital input line to tune up your sensing resistor value will be frustrating. Instead, monitor the voltage across your sensing resistor with a digital voltmeter (DVM) or oscilloscope, as you adjust your optical geometry and sensing resistor vale.		Using a digital input line to tune up your sensing resistor value will be frustrating. Instead, monitor the voltage across your sensing resistor with a digital voltmeter (DVM) or oscilloscope, as you adjust your optical geometry and sensing resistor vale.

LIMS at 19:51, 27 December 2006

2006-12-27T19:51:40Z

← Older revision		Revision as of 14:51, 27 December 2006
Line 49:		Line 49:

	In infrared (IR), I have used the QED123 IRED (clear pink package) at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The LTR-4206E (IR transparent black package) phototransistor passed about 300uA at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees).		In infrared (IR), I have used the QED123 IRED (clear pink package) at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The LTR-4206E (IR transparent black package) phototransistor passed about 300uA at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees).

			The

	Using a digital input line to tune up your sensing resistor value will be frustrating. Instead, monitor the voltage across your sensing resistor with a digital voltmeter (DVM) or oscilloscope, as you adjust your optical geometry and sensing resistor vale.		Using a digital input line to tune up your sensing resistor value will be frustrating. Instead, monitor the voltage across your sensing resistor with a digital voltmeter (DVM) or oscilloscope, as you adjust your optical geometry and sensing resistor vale.

LIMS at 19:47, 27 December 2006

2006-12-27T19:47:43Z

← Older revision		Revision as of 14:47, 27 December 2006
Line 46:		Line 46:
	'''Some favorite Emitters and Receivers'''		'''Some favorite Emitters and Receivers'''

	In visible light (red), I have used the SLI-580UT3F LED at 30mA, which throws a bright and narrow cone of illumination (~10 degrees). The PDB-C134 (clear package) photodiode passed about 1.5uA photocurrent at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees).		In visible light (red), I have used the SLI-580UT3F LED (clear package)at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The PDB-C134 (clear package) photodiode passed about 1.5uA photocurrent at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees).

			In infrared (IR), I have used the QED123 IRED (clear pink package) at 30mA, which throws a bright and narrow cone of illumination (~15 degrees). The LTR-4206E (IR transparent black package) phototransistor passed about 300uA at a range of about 3cm with a white paper reflector. It is also narrow-cone (~30 degrees).

			Using a digital input line to tune up your sensing resistor value will be frustrating. Instead, monitor the voltage across your sensing resistor with a digital voltmeter (DVM) or oscilloscope, as you adjust your optical geometry and sensing resistor vale.