Remote controls for infrared experimentsJay S. Huebner and N. Sundaralingam Citation: American Journal of Physics 66, 544 (1998); doi: 10.1119/1.18824 View online: http://dx.doi.org/10.1119/1.18824 View Table of Contents: http://scitation.aip.org/content/aapt/journal/ajp/66/6?ver=pdfcov Published by the American Association of Physics Teachers Articles you may be interested in Numerical investigation of optical Tamm states in two-dimensional hybrid plasmonic-photonic crystal nanobeams J. Appl. Phys. 116, 043106 (2014); 10.1063/1.4891222 Generalized scattering control using cut-wire-based metamaterials Appl. Phys. Lett. 98, 221105 (2011); 10.1063/1.3597628 Remotely controlled laboratories: Aims, examples, and experience Am. J. Phys. 76, 374 (2008); 10.1119/1.2885058 Large positive and negative Goos-Hänchen shifts from a weakly absorbing left-handed slab J. Appl. Phys. 98, 043522 (2005); 10.1063/1.2034084 Decoding the TV remote control Phys. Teach. 38, 6 (2000); 10.1119/1.880436
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Remote controls for infrared experimentsJay S. Huebnera)
Physics Program, Department of Natural Sciences, University of North Florida, Jacksonville,Florida 32224-2645
N. Sundaralingamb)
College of Arts and Sciences, Edward Waters College, Jacksonville, Florida 32209
~Received 20 June 1997; accepted 17 October 1997!
Digital IR remote control devices1 and incandescent lampselectrically heated only to red provide convenient and inex-pensive sources of IR for optics experiments, facilitating stu-dent exploration of this important and neglected area. IR canbe made visible using commercial IR sensor cards.2 When IRfrom a remote is directed to the sensitive area of these cards,yellow–orange flashes emanate. These flashes can be seenseveral rows away in a lighted classroom, and from across adarkened room. Students can tell from such demonstrationsthat the IR is flashing, suggesting some code, but the flashesare much too fast for the sequence to be determined fromthese observations.
Simple experiments can be conducted with remotes andsensor cards to determine some basic physical properties ofIR. For example, opaque objects, like keys and pencils, castshadows; common mirrors reflect IR; white cloth and paperscatter it; black cloth and paper absorb it; red filters~typi-cally! transmit it; and so on. If students are given or purchasetheir own sensor cards, they can do experiments to investi-gate the IR emitted by remotes in their homes. They caneven make qualitative observations using household appli-ances which respond to IR as their IR detectors. For ex-ample, will their TV respond to their IR remote when thesignal is bounced off the ceiling, an opposite wall, window,through several layers of tissue, plastic wrap, or a glass ofmilk? They may be pleased to demonstrate their results toothers, perhaps even suggesting that surfing the TV channelsfrom the couch has redeeming educational value.
Most science students in industrialized countries knowhow to use IR remotes to control TVs, VCRs, etc, but ourexperience suggests few know much about IR, or how itcommunicates the desired information. One can pique thestudents’ interest by suggesting the above home experiments,and by asking, for example, ‘‘When programming the VCRwith an IR remote, why doesn’t the TV respond?’’
The chromatic aberration of a simple converging glasslens can be easily observed using an incandescent counterlamp ~with clear glass and a linear filament! as the object,demonstrating different focal lengths for blue and red light.3
These results may be extended to IR by using an IR sensorcard on the screen with the same lamp behind a filter whichtransmits only IR. Suitable IR filters are available from manysources.4 The object may also be a flashing IR remote. Thespectra of IR emitted from several commercial remotes, thefluorescence of a sensor card, and light from a cloudy sky,recorded on an Oceans Optical spectrometer,5 are shown inFig. 1.
In more advanced labs, with more sophisticated equip-ment, experiments may be done using IR remotes as flash-lights for IR sensitive video cameras, night vision equip-ment, and IR imaging devices.6 If oscilloscopes areavailable, photodiodes can be used to detect IR intensityvariations in time and space.7 Storage oscilloscopes aid datarecording and analysis8 and digital oscilloscopes are evenbetter.9 Motorola MRD 500 photodiodes function well in theIR, are inexpensive, yet fast enough to show all IR variationsfrom IR remotes. All oscilloscope traces of IR presented inthis work were recorded with a MRD 500 photodiodes sol-
Fig. 1. The spectra from the sky on a rainy day, emissions of three IRremotes, and fluorescence of an IR sensor card, all recorded on an OceanOptics spectrometer. The vertical scale is in arbitrary units, the horizontalscale is in nm. For reference, human vision extends from;400 to;700 nm.
APPARATUS AND DEMONSTRATION NOTES
Daryl W. Preston,EditorDepartment of Physics, California State University, Hayward, California 94542
This department welcomes brief communications reporting new demonstrations, laboratory equip-ment, techniques, or materials of interest to teachers of physics. Notes on new applications of olderapparatus, measurements supplementing data supplied by manufacturers, information which, while notnew, is not generally known, procurement information, and news about apparatus under developmentmay be suitable for publication in this section. Neither theAmerican Journal of Physicsnor the Editorsassume responsibility for the correctness of the information presented. Submit materials toDaryl W. Preston,Editor.
544 544Am. J. Phys.66 ~6!, June 1998 © 1998 American Association of Physics Teachers
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dered directly to a coaxial cable which was terminated with50-V resistance on a Hewlett–Packard 54522A digital oscil-loscope.
The output IR power of three remotes, measured with aThorLabs optical power meter,10 was;1.2 mW for an NEC~model 9022!, and ;0.3 mW for both the One-for-All~model URC-2086!, and Pioneer~model BNR!. The peakemission wavelengths from these remotes, as shown in Fig.1, were 931.5, 929, and 948 nm, respectively.
Figure 2~a!, ~b!, and ~c! shows the IR flashing sequencewhich controls a Pioneer cable~to TV! converter ~modelBC-4125NSP! at several oscilloscope sweep speeds. The IRsignals are seen to be composed of periods when the IR isflashing at 40 kHz, Fig. 2~a!, punctuated by dark~off! peri-ods, seen in Fig. 2~b! and~c!. When a key of this remote washeld down the entire signal was repeated;10 times per s~not shown!.
The IR signals were converted into digital format~transistor–transistor logic signals! by an IR detector stage inthe Pioneer converter, shown in Fig. 2~d!. The detector out-put is seen to become logic 0~i.e.,;0 V! when the remote isflashing at 40 kHz and logic 1 (;5 V) when it is not flash-ing. There were propagation delays,;40ms for the on~logic 1 to 0! transitions, and;400ms for the off transitions.
Figure 3 shows the IR flashing sequence for four othervendors. Two protocols for encoding data in IR signals fromhand-held remotes are discussed in informal literature foundon the Internet.11 Two popular standard are RC-5 and RECS-80. The latter encodes logic 0 after an IR burst by having theIR be off for a period of twice the burst duration, and logic 1by having the IR be off for thrice the burst duration. TheRC-5 protocol specifies 14 bits, the first three of which aretiming bits. In RC-5 logic 1 is encoded with an IR burst, andlogic 0 with the IR being off, equal time intervals being usedfor each bit.
The Archer signals, one example of which is shown asFig. 3~a!, have some characteristics of the RECS-80 protocol
in that the space between sequential IR bursts vary in dura-tion between two values when the message contents arechanged. This changes the total signal duration. The Pioneersignals, shown in Fig. 2, have an;8-ms header followed byan ;4-ms off period. The parts of the signal following thatoff period have some characteristics of the RC-5 protocol,although there are differences since there are more than 14bits. The first three bits are used to identify the target device~i.e., are address bits, see below! and are not just timing bits,if they are used as timing bits. Additionally, the overalllength of the Pioneer signals were longer for addressing TVs,VCRs, and CD players than for addressing the converter.
The analysis of the IR signals was simplified by using thePioneer IR detector’s digital output. Since this digital outputmay only be valid when the signal protocol is consistent withPioneer’s design criteria, only Pioneer signals are consideredfurther here.
The location of certain encoded data can be determined bycomparing signals with small differences in message data.Two examples are shown in Fig. 4. Trace~a! shows thedigital signal for ‘‘0’’ addressed to a Pioneer CD player.Trace ~b! was produced by subtracting the digital trace for‘‘1’’ addressed to the same device from trace~a!, thus show-ing the difference between the traces for ‘‘0’’ and ‘‘1.’’ Thissubtraction was accomplished in the oscilloscope, and illus-trates one aspect of the utility of digital oscilloscopes. Trace~c! shows the digital trace for ‘‘0’’ addressed to a PioneerVCR. Trace~d! was produced by subtracting the trace for‘‘0’’ addressed to a Pioneer TV from trace~c!, thus showingthe difference between the signals ‘‘0’’ addressed to a Pio-neer VCR and TV. These and other such traces illustrate thatthose parts of the signals which have nonzero values in Fig.4~d! are address bits~i.e., they identify or address the targetdevice!.
The procedure just illustrated can potentially identify theuse of all bits which can be changed in a particular set of
Fig. 2. The upper 3 traces,~a!, ~b!, and~c!, show the photodiode response to IR signals from the Pioneer remote signaling ‘‘1’’ addressing a Pioneer converter.These signals were recorded at 8 mV, and 100ms, 2 ms, and 10 ms/div, respectively. The lower trace,~d!, shows the digital output of the Pioneer converter’sIR detector for the same signal, at 4 V and 2 ms/div.
545 545Am. J. Phys., Vol. 66, No. 6, June 1998 Apparatus and Demonstration Notes
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RC-5 type signals. Different procedures would be requiredfor RECS-80 type signals since changing the first bit from 0to 1 delays all subsequent bits.
The Pioneer detector’s response to the frequency of pulsesin IR bursts was investigated by using a gated pulse genera-tor to drive an IR diode signaling the detector, and varyingthat pulse frequency. The Pioneer detector responded cor-rectly providing the IR pulse repetition rate was.;2 kHz. A significant number of errors occurred at lowerpulsing rates.
The IR power required to reliably operate the Pioneer con-verter was below our capacity to measure directly, but wasestimated assuming a 1/r 2 dependence of the beam intensityin the middle of the beam beyond 1 m inarrangements wherescattered IR did not reach the detector. In the absence ofinterfering IR, the converter could be controlled by the pio-neer remote from;13 m, where the IR power was estimatedto be;0.2m W/m2. Outside on a cloudy day, with interfer-ing natural IR~see Fig. 1!, the converter could only be con-
Fig. 3. The photodiode response from the One-for-All remote, programmed to signal ‘‘1’’ to cable boxes from Archer~a!, Hamlin ~b!, Gemini~c!, and Zenith~d!, all recorded at 20 mV and 10 ms/div.
Fig. 4. Traces~a! and~c! are digital signals from the Pioneer IR detector, responding to IR signals generated by the One-for-All remote, programmed to signal‘‘0’’ to a Pioneer CD player~a! and ‘‘0’’ to a Pioneer VCR~c!. Trace~b! is trace a minus the digital signal generated from signaling ‘‘1’’ to a Pioneer CDplayer, thus showing the difference between the data ‘‘0’’ and ‘‘1.’’ Trace~d! is trace~c! minus the digital signal generated from signaling ‘‘0’’ to a PioneerTV, thus showing the difference between the signal ‘‘0’’ addressed to a Pioneer CD player and ‘‘0’’ addressed to a Pioneer TV. All traces were recorded at10 ms/div.
546 546Am. J. Phys., Vol. 66, No. 6, June 1998 Apparatus and Demonstration Notes
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trolled from within ;10 m. At 10 m, the IR power wasestimated to be;0.3m W/m2. The relatively high IR detec-tor sensitivity was achieved at the cost of detector instability,as evidenced by the fact that with no IR input the detectoroutput randomly switched from logic 1 to 0 and quickly backabout five times per s. This switching is acceptable in thisapplication since the probability of its generating a correctheader, address, and data sequence is extremely unlikely.
The ideas developed in this note have wider applicationthan just for IR and remotes. For example, by straightfor-ward generalizations, the operation of bar codes scannersused to sort the US mail, identify moving railroad cars, andprice products at supermarket checkout counters, can be ex-plained. A primitive bar code was made with strips of blacktape of varying width on white paper. A primitive bar codereader suitable for lecture demonstrations was made by tap-ing a MRD 500 photodiode attached to a coaxial cable to theside of a laser pointer so red light reflected back to thepointer also illuminates the photodiode. Then, with the cableconnected to an oscilloscope, and the pointer on, passing thebeam over the bar code produced digital traces comparableto those described in this work. Another application involvesthe search for extraterrestrial intelligence~SETI!. Radio hasbeen used for SETI over the past;40 years, without suc-cess. A recent paper12 suggests pulsed optical signals mayhave significant advantages for communicating over inter-stellar distances, and therefore may be arriving undetected onEarth.
ACKNOWLEDGMENTS
We thank Ray Richards for technical advice and assis-tance. The support of this work by the US and Florida De-partments of Transportation by partially funding UNF’s Ap-plied Optics Laboratory through the Institute of PoliceTechnology and Management is gratefully acknowledged.
a!Electronic mail [email protected]!Electronic mail [email protected] remotes have been developed using ultrasound, radio, and IR,
but the low price and high reliability of IR remotes have allowed them todominate the consumer market. Ultrasound remotes can be distinguishedby screens or grills which form the ultrasound ports. IR remotes usuallyhave either a dark red plastic IR window, or an exposed IR diode, whichappears as a clear plastic bulb emerging through the end of the device.Radio remotes generally broadcast through their plastic cases and have noobvious window or port. Programmable IR remotes, such as the One-for-All model used here, retail at department stores for;$20.
2Catalog No. 276-1099, Radio Shack,;$6 each. These cards respond toIR from 0.7 to 1.3mm. During use, they must be periodically ‘‘recharged’’with daylight or light from a fluorescent lamp, for;10 s.
3J. S. Huebner, M. D. Reynolds, and T. L. Smith,Basic Astronomy Labs~Prentice-Hall, Upper Saddle River, NJ, 1996!, pp. 8-1 through 8-8.
4Potential filters can be tested for IR transmission by seeing if IR remotescan control appliances through them, and observing~with human eyes! ifvisible is transmitted. The following have been found to make suitable IRfilters for these experiments:~A! the front piece of many IR remotes;~B!cobalt blue glass, which transmits IR and blue, but a red metal filamentdoes not generate much blue, leaving only IR;~C! the overexposed anddeveloped color film strips usually produced from each roll of photo-graphic film;~D! stacked blue and red Lee Filters, which together transmitIR but not visible. These filters can obtained in 0.6 by 0.6-m sheets fromJacksonville Stage Lighting, 640 N. Lane Ave., Jacksonville, FL 32254.Transmission spectra packaged with small filter samples are available.More than 100 different types of filters available for,;$10 each, whichwhen cut into pieces make 535-cm filters for ;7 cents each. We use20320-cm color filters in exercises in basic astronomy labs where stu-dents investigate the light which passes through their closed eye lids.
5Model SD2000, Ocean Optics, Inc., 1237 Lady Marion Lane, Dunedin, FL34698-5314.
6PAS-100 Enhanced Infrared Viewer, Stano Components, P. O. Box 2048,Carson City, NV 89702.
7J. S. Huebner and T. J. Allen, ‘‘Physics with photo-cells and an oscillo-scope,’’ Phys. Teach.16, 31–33~1978!.
8J. S. Huebner and J. T. Humphries, ‘‘Storage oscilloscopes in the modernphysics laboratory,’’ Am. J. Phys.42, 870–876~1974!.
9M. F. Masters and R. E. Miers, ‘‘Use of a digital oscilloscope as a spec-trum analyzer in the undergraduate laboratory,’’ Am. J. Phys.65, 254–255~1997!.
10Model S22MM, ThorLabs, Inc., 435 Route 206, Newton, NJ 07860-0366.11http://falcon.arts.cornell.edu/;dnegro/IR/rc5.html, and
http://falcon.arts.cornell.edu/;dnegro/IR/IR.html.12Jeff Hecht, ‘‘Modern optics may make optical SETI practical,’’ Laser
Focus World, July 1996, pp. 99–104.
GOOD TEACHERS, POOR TEACHERS
The human mind is essentially one, but the directions it may take are many, and it is easy to seethat people in general divide into those with a bent toward numbers and science and those whotake naturally to literature, history, and the arts.
There are further subdivisions, but these two are perhaps the largest and most clearly marked.The split occurs early in life and accounts for the fact that from the very first grade one child‘‘loves’’ math and another hates it. This is the beginning of the school’s difficulty. Especiallywhen math courses are optional and student opinion tags them as difficult, there will be few takersand the outcry about the paucity of math and science majors will go on forever. What is seldomnoticed is that the trait in students who favor math is also the cause of much poor teaching. For themind that feels at home with math is likely to lack the qualities that make a good teacher.
Jacques Barzun,Begin Here—The Forgotten Conditions of Teaching and Learning~The University of Chicago Press,Chicago, 1991!, p. 78.
547 547Am. J. Phys., Vol. 66, No. 6, June 1998 Apparatus and Demonstration Notes
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