Harvalik, Zaboj V.

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Journal of the Arkansas Academy of Science Volume 5 Article 24 1952 Random Wave Form Generator Zaboj V. Harvalik University of Arkansas, Fayetteville Follow this and additional works at: https://scholarworks.uark.edu/jaas  Part of the Electronic Devices and Semiconductor Manufacturing Commons Recommended Citation Harvalik, Zaboj V. (1952) "Random Wave Form Generator," Journal of the Arkansas Academy of Science: Vol. 5 , Article 24. Available at: https://scholarworks.uark.edu/jaas/vol5/iss1/24 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu. A RANDOM WAVE FORM GENERATOR 1*ZABOJ V. HARVALIKUniversity of ArkansasIn physiological research it is sometimes desirable to use electric cur-rents of random wave forms for stimulation. Usually, electric generators usedfor stimulation produce, besides direct current, sinusoidal, triangular, orsquare wave electric currents only. Attempts have been made to generate ran-domized wave forms by electronic means. These circuits, however, are quitecomplicated and limited in the variety of random waves produced.It was, therefore, desirable to design a random wave form generator devia-ting from electronic wave shaping. The generator described in this paper isbased upon the following principle: Light emitted from a light source (L)(Figure 1), and passing through discriminating slits (S) and (AS), is reduced inits intensity by a moving paper mask of black paper (M) having the shape of therandom wave desired. The paper mask is mounted on a rotating cylindrical drum( RD). The light beam modulated. by the paper mask reaches the photocell (P).The photocell produces a photo current of exactly the same wave form as thelight beam is modulated by the paper mask.This random wave form current is a pulsating direct current of recurrentperiodicity. The random wave form photo-current can be directly applied to theobject to be stimulated. Ifthe output energy is too low, electronic amplifica-tion would increase the output.Description of the Instrument.The instrument consists of a light source (L) (6 V, 30 cp bulb, supplied bya 6 V transformer) (Figure 1), a drum ( RD) of transparent material, such asglass or lucite, driven by a d- Volt automobile fan motor of variable speed, aground glass (G) diffusor attached to the slit (S) (2 mm wide), a slit of ad-justable width (AS) which acts as a discriminator, a collimating cylindricallens (CL), and a photocell (P) mounted in a light-tight compartment with itsterminals (PT).The variation of speed of the motor is achieved by a variable resistor(20 ohms, 2A) shunting the rotor of the motor.The transparent cylindrical drum (Figure 1, RD) , mounted on a toothedwheel, is exactly centered. The toothed wheel is geared to the axle of themotor in the ratio 10: 1 ( 10 revolutions of the motor causes 1 revolution of thedrum).The mask (M) of black paper, cut into any desired wave form, is insertedinto the drum (RD). A plastic transparent strip, bent into cylindrical shape,should be inserted into the drum (RD) to keep the mask (M) in place and preventwrinkling and bending of wave form features of the mask;The discriminator slit (AS) is adjustable from 0.05 mm to 2.0 mm and per-mits the discrimination of the wave form. The narrower the slit the better thediscrimination. However, the output from the photocell decreases with the de-crease of the slit width.To focus the slit (AS) on the photocell, a cylindrical lens (CL) is placedbetween the slit and the photocell. The lens has a focal length of 12.5 mm.The photocell (P) is a General Electric barrier-layer cell, Catalog No.88X565, the current of which is fed into the output terminal. A double-pole-double- throw switch, wired as a commutator, permits the change of polarity ofthe stimulus (Figure 2).In case an AC is desired the photocell output (Figure 2) is fed into atransformer. A female four-contact telephone jack permits switching the outputof the photocell into the transformer. This transformer has a winding ratio ofThis paper was presented at the 33rd Annual Meeting of the Arkansas Academy of Science,May 1949.'Research Paper No. 1045 Journal Series. University of Arkansas.129Journal of the Arkansas Academy of Science, Vol. 5 [1952], Art. 24Published by Arkansas Academy of Science, 1952130 ARKANSAS ACADEMY OF SCIENCE1:1 (200 turns primary and secondary). The core of the transformer is laminatedPermalloy. The positioning of the zero axis of the AC is achieved by a potenti-ometer and commutater in the circuit of the secondary coil of the transformer.Performance of the Instrument.Performance tests of the instrument have been made as follows: A repre-sentative random wave form has been cut on black paper (Figure 3) and insertedinto mask holder (rotating drum). The photo current of random wave form wasrecorded by a GE recording voltmeter. Output recordings have been made with thesame wave form mask for direct current (Figure 4-A), alternating current (Figure4-B), alternating current output positioned by the positioning circuit (Figure4-C), and alternating current output, amplified two times of Figure 4-C, posi-tioned by the positioning circuit (Figure 4-D). Figure 4-A shows that the dis-crimination of the wave form is better than 1% when a slit width of 0.5 mm isused.Performance tests using a cathode ray oscilloscope as wave form indicatorrevealed that the lamp used as supply source must have an inert filament inorder to prevent a 60-cycle illuminous modulation when connected by a trans-former to the power line. However, ifa 6> V storage battery is used as powersource for the lamp no interfering modulation was observed.To amplify the random wave form currents (DC or AC) a two-stage amplifierwill be satisfactory for most cases.130Journal of the Arkansas Academy of Science, Vol. 5 [1952], Art. 24https://scholarworks.uark.edu/jaas/vol5/iss1/24Figure 4131A RANDOM WAVE FORM GENERATOR131Journal of the Arkansas Academy of Science, Vol. 5 [1952], Art. 24Published by Arkansas Academy of Science, 1952132Journal of the Arkansas Academy of Science, Vol. 5 [1952], Art. 24https://scholarworks.uark.edu/jaas/vol5/iss1/24

Random Wave Form Generator

ScholarWorks@UARK

Journal of the Arkansas Academy of ScienceVolume 5 Article 241952Random Wave Form GeneratorZaboj V. HarvalikUniversity of Arkansas, FayettevilleFollow this and additional works at: http://scholarworks.uark.edu/jaasPart of the Electronic Devices and Semiconductor Manufacturing CommonsThis article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able toread, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking priorpermission from the publisher or the author.This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academyof Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu, ccmiddle@uark.edu.Recommended CitationHarvalik, Zaboj V. (1952) "Random Wave Form Generator," Journal of the Arkansas Academy of Science: Vol. 5 , Article 24.Available at: http://scholarworks.uark.edu/jaas/vol5/iss1/24A RANDOM WAVE FORM GENERATOR 1*ZABOJ V. HARVALIKUniversity of ArkansasIn physiological research it is sometimes desirable to use electric cur-rents of random wave forms for stimulation. Usually, electric generators usedfor stimulation produce, besides direct current, sinusoidal, triangular, orsquare wave electric currents only. Attempts have been made to generate ran-domized wave forms by electronic means. These circuits, however, are quitecomplicated and limited in the variety of random waves produced.It was, therefore, desirable to design a random wave form generator devia-ting from electronic wave shaping. The generator described in this paper isbased upon the following principle: Light emitted from a light source (L)(Figure 1), and passing through discriminating slits (S) and (AS), is reduced inits intensity by a moving paper mask of black paper (M) having the shape of therandom wave desired. The paper mask is mounted on a rotating cylindrical drum( RD). The light beam modulated. by the paper mask reaches the photocell (P).The photocell produces a photo current of exactly the same wave form as thelight beam is modulated by the paper mask.This random wave form current is a pulsating direct current of recurrentperiodicity. The random wave form photo-current can be directly applied to theobject to be stimulated. Ifthe output energy is too low, electronic amplifica-tion would increase the output.Description of the Instrument.The instrument consists of a light source (L) (6 V, 30 cp bulb, supplied bya 6 V transformer) (Figure 1), a drum ( RD) of transparent material, such asglass or lucite, driven by a d- Volt automobile fan motor of variable speed, aground glass (G) diffusor attached to the slit (S) (2 mm wide), a slit of ad-justable width (AS) which acts as a discriminator, a collimating cylindricallens (CL), and a photocell (P) mounted in a light-tight compartment with itsterminals (PT).The variation of speed of the motor is achieved by a variable resistor(20 ohms, 2A) shunting the rotor of the motor.The transparent cylindrical drum (Figure 1, RD) , mounted on a toothedwheel, is exactly centered. The toothed wheel is geared to the axle of themotor in the ratio 10: 1 ( 10 revolutions of the motor causes 1 revolution of thedrum).The mask (M) of black paper, cut into any desired wave form, is insertedinto the drum (RD). A plastic transparent strip, bent into cylindrical shape,should be inserted into the drum (RD) to keep the mask (M) in place and preventwrinkling and bending of wave form features of the mask;The discriminator slit (AS) is adjustable from 0.05 mm to 2.0 mm and per-mits the discrimination of the wave form. The narrower the slit the better thediscrimination. However, the output from the photocell decreases with the de-crease of the slit width.To focus the slit (AS) on the photocell, a cylindrical lens (CL) is placedbetween the slit and the photocell. The lens has a focal length of 12.5 mm.The photocell (P) is a General Electric barrier-layer cell, Catalog No.88X565, the current of which is fed into the output terminal. A double-pole-double- throw switch, wired as a commutator, permits the change of polarity ofthe stimulus (Figure 2).In case an AC is desired the photocell output (Figure 2) is fed into atransformer. A female four-contact telephone jack permits switching the outputof the photocell into the transformer. This transformer has a winding ratio ofThis paper was presented at the 33rd Annual Meeting of the Arkansas Academy of Science,May 1949.'Research Paper No. 1045 Journal Series. University of Arkansas.129Journal of the Arkansas Academy of Science, Vol. 5 [1952], Art. 24Published by Arkansas Academy of Science, 1952130 ARKANSAS ACADEMY OF SCIENCE1:1 (200 turns primary and secondary). The core of the transformer is laminatedPermalloy. The positioning of the zero axis of the AC is achieved by a potenti-ometer and commutater in the circuit of the secondary coil of the transformer.Performance of the Instrument.Performance tests of the instrument have been made as follows: A repre-sentative random wave form has been cut on black paper (Figure 3) and insertedinto mask holder (rotating drum). The photo current of random wave form wasrecorded by a GE recording voltmeter. Output recordings have been made with thesame wave form mask for direct current (Figure 4-A), alternating current (Figure4-B), alternating current output positioned by the positioning circuit (Figure4-C), and alternating current output, amplified two times of Figure 4-C, posi-tioned by the positioning circuit (Figure 4-D). Figure 4-A shows that the dis-crimination of the wave form is better than 1% when a slit width of 0.5 mm isused.Performance tests using a cathode ray oscilloscope as wave form indicatorrevealed that the lamp used as supply source must have an inert filament inorder to prevent a 60-cycle illuminous modulation when connected by a trans-former to the power line. However, ifa 6> V storage battery is used as powersource for the lamp no interfering modulation was observed.To amplify the random wave form currents (DC or AC) a two-stage amplifierwill be satisfactory for most cases.130Journal of the Arkansas Academy of Science, Vol. 5 [1952], Art. 24http://scholarworks.uark.edu/jaas/vol5/iss1/24Figure 4131A RANDOM WAVE FORM GENERATOR131Journal of the Arkansas Academy of Science, Vol. 5 [1952], Art. 24Published by Arkansas Academy of Science, 1952132Journal of the Arkansas Academy of Science, Vol. 5 [1952], Art. 24http://scholarworks.uark.edu/jaas/vol5/iss1/24

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Random Wave Form Generator

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