/,-^%\ (P 4 .^fe.% J>*.<tifc\ 
 
 
 
 
 ■^ 
 
 
 ^5°^ 
 
 
•?*X' ,.♦ 
 
 o*' -\--r.r-- ^ '^•^P'o*' v : ---> "V^^*** v-tt- 
 
 J* . 
 
 J* •' 
 
 V %*^V V^V %^V V^*V V 
 
 W 
 
 <W> 
 
 
 
 ^' A° ^ 
 
 > "V 
 
 *^ ** 
 
 \ '-IK?-* «^ 
 
 
 1~ .1 
 
 
 «f» ' 
 
 <> *'TVT« ,0 X 
 
 t* « 
 
 • » * .A 
 
 <* *'TVT* ,G* 
 
 
 "oV" 
 
 ^V. V 
 
 t* A v *^«. 
 
 xs 
 
 
 ^Qt 
 
 
 <U *'TV.* ,0 
 
 
 
 „«• 
 
 
 
 
 A<^ 
 
 
 
 
 
 .0° V*^-'^ 
 
 
 V ^ -i^-°- /-^i% ^.i^-% 
 
 
 
 »H<^ 
 
 •>o* 
 
 
 
 
 r> 
 
 to 
 
 aT o • - _ . » O"^ 
 
 ^r %. • • ° a V. " ' <V 
 
 H°* 
 
IC 
 
 8939 
 
 Bureau of Mines Information Circular/1983 
 
 Passive Encoder for Range Knobs 
 
 By William H. Schiffbauer 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
Information Circular 8939 
 
 Passive Encoder for Range Knobs 
 
 By William H. Schiffbauer 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
 James G. Watt, Secretary 
 
 BUREAU OF MINES 
 Robert C. Horton, Director 
 
(It) 
 
 ,%rt 
 
 
 This publication has been cataloged as follows: 
 
 Schiffbauer, William H 
 
 Passive encoder for range knobs. 
 
 (Information circular ; 8939) 
 
 Supt. of Docs, no.: I 28.27:8939. 
 
 1. Computer interfaces. I. Title. II. Title: Range knobs. III. 
 Series: Information circular (United States. Bureau of Mines) ; 8939. 
 
 TN295.U4 [TK7887.5] 622s [621. 3819'5832] 83-600134 
 
CONTENTS 
 
 Page 
 
 Abstract 1 
 
 Introduction 1 
 
 Background ' 2 
 
 Description 3 
 
 Application 4 
 
 Operation 4 
 
 Limitations 4 
 
 Conclusions 4 
 
 ILLUSTRATIONS 
 
 1. Passive encoder for range knobs (PERK) 2 
 
 2 . PERK electrical schematic 3 
 
 3. Instrument with the label 5 
 
 4 . Applying the PERK 5 
 
 5. Instrument with the PERK 6 
 
 6. Instrument with the custom knob 6 
 
 7. Suggested spacer 7 
 
 8. Completed installation 7 
 
PASSIVE ENCODER FOR RANGE KNOBS 
 
 By William H. Schiffbauer 1 
 
 ABSTRACT 
 
 The Bureau of Mines has developed a passive encoder for range knobs, 
 a device that automates the task, of obtaining the range settings from 
 devices or instruments to be input to microcomputers. It is easily 
 constructed and installed and will not disrupt the device to which it 
 is being attached. It consists of a custom knob and a small printed 
 circuit board that has light-emitting diodes and magnetic reed switches 
 attached. A ribbon cable connects it to a microcomputer. This encoder 
 eliminates one source of human error in an automated process. 
 
 INTRODUCTION 
 
 The microcomputer development laboratory of the Bureau of Mines ap- 
 plies technology to experimental research. Its objectives are to auto- 
 mate repetitious tasks, increase accuracy, and save time in doing 
 research. This work sometimes involves connecting the outputs of in- 
 struments to microcomputers. Some instruments do not provide enough 
 outputs for the microcomputer to process its data. A search was con- 
 ducted for a commercially available product to accomplish this task, 
 but a suitable device could not be found. The Bureau then developed a 
 device called a passive encoder for range knobs (PERK) (fig. 1), which 
 provided a microcomputer-compatible output. It was easy to install, 
 and the cost was very low. One data-logging project alone used six 
 PERK's; their performance was outstanding. 
 
 This report provides complete details of this device. 
 Electronics technician, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
 
BACKGROUND 
 
 The Bureau developed the PERK to moni- 
 tor the output of gas analyzers in a 
 microcomputer-controlled experiment. The 
 PERK was needed to fill a gap the gas- 
 analyzing instruments did not provide in 
 the form of an output. Some gas analyz- 
 ers have only one analog output for eight 
 ranges of gas concentrations. The fol- 
 lowing tabulation is an example of the 
 ranges and the outputs provided on one 
 nitrogen oxide (N0 X ) analyzer: 
 
 Range 
 
 Gas 
 
 
 Output, 
 
 position 
 
 cone 
 ppn 
 
 • > 
 
 L 
 
 Vdc 
 
 1 
 
 0- 
 
 5 
 
 0-5 
 
 2 
 
 0- 
 
 10 
 
 0-5 
 
 3 
 
 0- 
 
 20 
 
 0-5 
 
 4 
 
 0- 
 
 50 
 
 0-5 
 
 5 
 
 0- 
 
 100 
 
 0-5 
 
 6 
 
 0- 
 
 200 
 
 0-5 
 
 7 
 
 0- 
 
 500 
 
 0-5 
 
 8 
 
 0-1, 
 
 000 
 
 0-5 
 
 Note that both the range and the output 
 voltage must be considered to know the 
 correct gas concentration. For example, 
 80 ppm on range 5 gives the same output 
 voltage as 160 ppm on range 6. 
 
 ,€?> 
 
 Scale, in 
 
 The instrument supplies only the out- 
 put voltage. Nothing is done to provide 
 an output for the range position. There- 
 fore, some method must be used to ob- 
 tain an output so the microcomputer will 
 know the correct gas concentration. This 
 range position information can be ob- 
 tained in one of two ways: 
 
 1. Manually enter the range informa- 
 tion into the microcomputer keyboard at 
 the appropriate time. 
 
 2. Automatically monitor the range 
 position by some mechanical or electrical 
 connection to the instrument. 
 
 The manual 
 limitations: 
 
 operation has several 
 
 1 . At the beginning of the process , 
 the operator must enter the correct range 
 into the microcomputer. 
 
 2. The operator must remember that 
 changes to the instrument's range can 
 only be made when the microcomputer is 
 stopped. 
 
 3. The collected data would be inac- 
 curate as the instrument's output voltage 
 approached or 5 Vdc because the instru- 
 ment should be on the next lower or upper 
 range position. This is because most in- 
 struments have their greatest accuracy 
 when reading between 80% and 100% of full 
 scale. 
 
 4. Valuable information could be lost 
 during range changing because the micro- 
 computer would be stopped. 
 
 These limitations left too 
 bilities for human error, so 
 tic approach was pursued. 
 
 many possi- 
 the automa- 
 
 FIGURE 1, - Passive encoder for range knobs (PtRK). 
 
 The first approach to automatically en- 
 code the range switch position was to try 
 to attach another section or wafer to the 
 switch. A few instruments were opened to 
 see if this was possible, but they were 
 packed tight with electrical and mechani- 
 cal hardware. Adding anything to them 
 
would require major modifications. To 
 avoid this problem, a more passive ap- 
 proach was pursued. It used the front 
 panel of the instrument and the range 
 switch knob. 
 
 Three methods were studied using 
 mechanical, magnetic, and optical 
 
 components. The mechanical and optical 
 components, however, were too bulky and 
 interfered with the function of other 
 knobs on the instruments. The components 
 selected for magnetic coupling were very 
 compact. These components fit on all the 
 instruments and were able to encode the 
 instrument's range position. 
 
 DESCRIPTION 
 
 Miniature magnetic reed switches and a 
 small magnet were selected to do the 
 range switch position encoding. When a 
 magnet passes over a switch, it closes. 
 Using this principle and these de- 
 vices, several test encoders were con- 
 structed. The result is the PERK shown 
 in figure 1. 
 
 Magnetic reed switches are small glass 
 capsules that are 1/2 in long and 1/8 in 
 in diameter. Each capsule houses two 
 metal contacts that come together in the 
 presence of a magnetic field. The mag- 
 netic reed switches were placed on a 
 printed circuit board at 30° increments, 
 to coincide with each range position. 
 The circuit board is 1/16 in thick and 
 shaped like a common protractor. It is 
 placed under the instrument's knob and 
 provides an individual output through an 
 edge connector for each of the magnetic 
 switches. Also, each switch had an asso- 
 ciated light-emitting diode (LED) at- 
 tached to it that lighted when the switch 
 closed. LED's are 1/8-in-diameter elec- 
 tronic devices that emit light when a 
 voltage is applied. The magnet used was 
 inserted into a small hole that was 
 drilled into the instrument's knob. When 
 the knob is turned and the magnet passes 
 over one magnetic switch, that switch 
 closes, an LED lights, and an output is 
 produced for one specific range position 
 of the instrument. 
 
 Figure 2 shows the design of the cir- 
 cuit board with the components mounted. 
 The magnetic reed switches are SI to S9 , 
 and the LED's are Dl to D9. A card edge 
 connector (PI) is used for ease of appli- 
 cation and removal of the PERK. It also 
 provides 5 Vdc to light the LED's and 
 
 /| 6 -in- thick printed circuit 
 board mounted with compon- 
 ents is encapsulated in ^/g- 
 in-thick clear plastic 
 
 KEY 
 D3-Diode 
 S4-Switch 
 
 Card edge^ i zj«567s9ioii 
 connector 
 
 PI 
 
 Rl-2700. 
 
 Pins on 05-in 
 centers 
 
 PASSIVE INSTRUMENTATION RANGE DECODER 
 
 1234567691011 
 
 Card edge 
 moting connector' 
 Jl 
 
 Magnet is inserted in hole 
 '/ 32 in from base '/£ in deep? 
 
 Card e 
 
 iqe Dip 
 
 pin 
 
 pin 
 
 15 
 
 2 
 
 2 
 
 3 
 
 14 
 
 4 
 
 3 
 
 5 
 
 13 
 
 6 
 
 4 
 
 7 
 
 12 
 
 8 
 
 5 
 
 9 
 
 II 
 
 10 
 
 6 
 
 II 
 
 10 
 
 ,D 
 
 p connector 
 
 ^\ 
 
 P2 
 
 II 1 1 1 1 1 
 
 MODIFIED KNOB 
 
 RIBBON CABLE 
 
 Ground 
 
 INTERFACE BOARD 
 
 FIGURE 2. - PERK electrical schematic. 
 
supplies the encoded output for each 
 range position. Rl is a current-limiting 
 resistor for the LED's. The circuit 
 board, with all the components mounted, 
 is then encapsulated with clear plastic 
 for protection. A piece of double-sided 
 tape is applied to the back of the PERK 
 so it can be attached to the instrument. 
 
 A ribbon cable with a card edge con- 
 nector (Jl) on one end and a DIP con- 
 nector (P2) on the other end connects the 
 
 PERK to an interface board (PC2). The 
 interface board connects to DIP connector 
 P2 via DIP connector J2. The 5-Vdc sup- 
 ply is attached to the board on termi- 
 nal strip TB2. R2 on PC2 is a current- 
 limiting resistor. The 5-Vdc power is 
 applied to the PERK through pin 4 of J2; 
 -5 Vdc is on pin 10. The encoded outputs 
 from the PERK come through J2 and go to 
 terminal strip TBI , where they are avail- 
 able as a 5-Vdc logic signal for applica- 
 tion to any other device. 
 
 APPLICATION 
 
 The first step is to copy the range in- 
 formation of the instrument onto a label, 
 as shown in figure 3. Then, remove the 
 knob and prepare the PERK by removing the 
 tape on its back to expose the sticky 
 surface (fig. 4). Next, stick the PERK 
 on the instrument. Figure 5 shows the 
 PERK when properly attached. The cus- 
 tomized knob is inserted onto the switch 
 shaft as shown in figure 6. Some 
 
 applications may require the addition of 
 spacers under the PERK to insure proper 
 spacing in relation to the knob. An ex- 
 ample of a suggested spacer is shown in 
 figure 7. When the PERK is properly 
 applied, attach the interface cable as 
 indicated in figure 8 to both the PERK 
 and the interface board. The unit is now 
 ready to connect to a computer. 
 
 OPERATION 
 
 Refer to figures 2 and 8. When power 
 is applied and the knob is in position 1, 
 the magnet in the knob causes SI to 
 close. This applies power to the LED 
 (Dl), causing it to light. It also sup- 
 plies 5 Vdc to pin 1 of card edge 
 connector PI, which is connected to posi- 
 tion 1 on terminal strip TBI of the 
 
 interface board. When the knob is turned 
 to position 2, 3, etc., the same thing 
 happens, but each position activates a 
 different set of parts and, in effect, 
 gives a unique 5-Vdc output for each knob 
 position. These outputs are provided on 
 TBI of the interface board and can be ap- 
 plied to a computer. 
 
 LIMITATIONS 
 
 This device was designed for instrument 
 switches that have 30° increments between 
 positions, but other instrument switches 
 can have increments of either 15° or 45°. 
 
 This method will not permit decoding of 
 15° switches; however, the 45° switches 
 can be monitored by the PERK printed cir- 
 cuit board. 
 
 CONCLUSIONS 
 
 The PERK is a device that performs a 
 critical task in an automated process. 
 It can be constructed by most electronic 
 laboratories with a few common and inex- 
 pensive electronic components. Although 
 this report discusses the use of the PERK 
 only on instrumentation and computerized 
 processes , it may be used in any number 
 
 of applications that require monitoring 
 of a knob's position. 
 
 Installation of the PERK under normal 
 circumstances takes less than 15 min. 
 After installation, the system operator 
 can forget about the instrument's range 
 position. The computer monitors the 
 
FIGURE 3- - Instrument with the label. 
 
 FIGURE 4. • Applying the PERK. 
 
FIGURE 5. - Instrument with the PERK. 
 
 FIGURE 6. = Instrument with the custom knob. 
 
FIGURE 7. - Suggested spacer. 
 
 Am - 
 
 FIGURE 3. Completed installation. 
 
 KtAtriOM 
 
range position continuously and uses that The PERK's simple construction, ease of 
 
 information to calculate the instrument's installation, and savings in material and 
 
 output. labor time makes it a significant devel- 
 opment. Operators of automated instru- 
 
 The Bureau has estimated that on one mentation processes should find the PERK 
 
 project the PERK's use saved 8 days of to be a valuable asset, 
 labor. 
 
 INT.-BU.OF MINES, PGH., PA. 26936 
 

 


 r ^9 
 
 ***** .'Jfef- ^ / ^ 
 
 ^6* 
 
 "oV" 
 
 ** °** "W&' *° ** 
 
 
 ,* v >: 
 
 
 4 4? % ' 
 
 *.">. V 
 
 
 c,^ 
 
 * *0 j> «. ° " • 
 
 ■» o 
 
 o V 
 
 
 
 -a5 ^ 
 
 
 w * 
 
 
 4> o°r e « ^ 
 
 
 
 ' ^ 
 
 
 
 
 * "^ 
 
 
 , .** /^tei'- ** .=.** .^vx-. ** A * /date**- **. ^* .>v/k-_ *,. A * .*«oK'. 
 
 / ..; 
 
 
 *v 
 
 v^ 1 
 
 
 * o 
 
 ■ ° AT ^ 
 
 
 **# 
 
 "\^<-V ^,C^> ,<^i.\ /.C^^o 
 
 ^**til*S 'JP'jiMkS' \^i^>o ' ' V^.-^i-X 
 
 <0 «£> *.,,• a-V- 
 
 
 ? 
 
 r oy 
 
 
f a <^ '?.?« .0* V ♦7KT» a <r 
 
 .„»- .g* V *T*Xv a 
 
 • j j5^s.^*^ o 
 
 
 
 o_ * 
 
 ■. ^ 
 
 a g* v *>???• a 
 
 ** a* ^Va* \ # 
 
 * -V v« °^ 
 
 
 
 
 " A V *V 
 
 
 "oV 
 
 
 v-o^ 
 
 
 
 J 3 ~* 
 
 
 ; 'w •■ 
 
 ^^ 
 
 c* * 
 
 
 
 ' ^ A^ • 
 
 
 -ov y :£§i^ ^o^ :*^IB: -ov* :]iflf^* ^o* •- 
 
 »?v 
 
 ^ "^ -J 
 
 A*> »wiw'* > 
 
 
 H o 
 
 - % ** -i<^; o o ^ > •*)£&• ^ a* •• 
 
 
 :- ^n< •« 
 
 *bt? 
 
 
 v- 
 
 I 
 
 40 .^ypsf <o «». 
 
 
 ^0< 
 
 
 
 
 
 
 "oV 
 
UBRA^ 0FC ' 
 
 NGRE sS 
 
 
 
 jii^Sa 
 
 1