N S
~ d
'-'-i '-'-i '-'-i ..
.050 .100 .150
DISTANCE
=
(d)Figure 12-Flux vs position. single pole har magnet
asymptotic to the zero flux axis, a slight change in the release point of the chip would require a large change in the movement of the magnet to reach the release point.
This is not desirable. If two magnets a.re used and are magnetized as shown in Figure 13, the flux versus gap position curve will tend to be sinusoidal. This is desir-able if the total travel of the magnet assembly can be limited to the nearly linear portion of the curve. Since the flux required for both operate and release points is positive, the negative portion of the curve would not be used. By inserting the two magnets in a "U" shaped shunt and magnetizing them in place with a specially shaped magetizing fixture, it is possible to produce the curve shown in Figure 14. The result of this is to move the majority of the sinusoid above the zero flux axis.
Figure 14 also shows the ma~l.Let assembly and the shape of the poles on each of the magnets.
sl
IC~IP
I
I
Is :
NI~d~
(
DISTANCE
=
(d)Figure 1:3--Flux VH position, double pole magnet
t
100
®
MAGNETIC (GAUSS) FLUX 100
j
50
.100 .150
DISTANCE
=
(d)Figw'e 14---Fiux V~ position, douhle pole, modified
The magnets are made of polyvinyl chloride filled with barium ferrite. This combination produces an ex-tremely stable, yet low cost, permanent magnet mate-rial. The shunt is soft iron which increases the magnet efficiency and helps to reduce the effect of stray· mag-netic fields. The chip package is made as thin as pos-sible to reduce the air gap. The magnet assembly with the chip package is shown in Figure 15. Referring to the specification on the chip, and relating these to the flux versus position curve, it is possible to establish the operate and release points of the key, as shown in Figure 16.
Figure 15-Chip package and magnet assembly
1000
500
-o
Key Travel in Inches
Figure 16-Operate and release ranges of key
Solid State Keyboard 157
Table I -Chip specifications
Parameter Minimum Maximum Units Operate Point (OP) 300 750 Gauss
Release Point (RP) 100 Gauss
Differen tial
(OP - RP) 150 Gauss
Supply Voltage 4.75 ;).25 Volts
Supply Current 15 rnA
(OFF Condition)
Output Voltage 3.4 3.6 Volts
(ON) @ 5V supply
Output Voltage 0.25 Volts
(OFF) 5000 ohm load
Output Current 10 rnA
(ON) (each terminal)
Reliahility test results
A variety of enviromnental tests have been made on the key chip integrated circuit, packaged as noted here-in. In addition to tests on functional performance on conventional chips, chips with special metallization patterns were prepared and packaged, such that junc-tion characteristics and Hall element output could be measured directly. This allows a more sensitive indica-tion of incipient de~adation than does functi '"lnal performance. Table II describes tests on four lots of devices. The results are in keeping with the reliability
Figure 17-Plunger magnet assembly
Table II - Reliahility test results
No. of Dem:ces Type of Test Environment Time Results
30 Functional, Normal Office 15 months Xo failures
magnetic actuation
15 Functional, 75 to 100 deg. F. 4~30 hrs. No failures
magnetic actuation
30 Hall element (V q) 70 deg. C. 1000 hrs. Maximum variation
90% R.H. of 2%
6 Collector junction 70 deg. C. 1000 hrs.' No change
VCBO @ 10 jJA 90% R.H.
expected of semiconductor devices, when designed, processed and packaged properly. These tests are
con-tinuing and others are being initiated.
Mechanical assembly
The magnet assembly is inserted into the key plunger which is shown in Figure 17 .:rrhe plunger magnet as-sembly is guided in the key housing by large area. guides.
We have shaped the top of. the plunger and the inside of the two-shot molded button so that the button is press fitted directly into the plunger, avoiding the conven-tional adaptor pin. In addition to lower cost this pro-vides the advantage of a low keyboard profile.
The chip package is inserted into slots in the housing which hold it in the gap of the magnet assembly. Two small tangs on the bottom of one side of the magnet shunt hold the return spring in place. This spring is designed to provide the two to five ounces of operating
Figure IS-Key assembly
Figure t9--Mounting rail-PC board assembly
force under minimum stress conditions, assuring long life without getting weak.
The key module, shown in Figure 18, is inserted into a mounting rail. The module snaps into the rail, which has clearance holes for the leads of the chip package to extend through it and be soldered into a printed circuit board. The mounting rails are welded to the end mount-ing bracket and the entire assembly is riveted to a PC board as shown in Figure 19. The printed circuit board provides the electrical connection between the key modules and a second PC board. The latter contains the electronics for encoding, t4e strebe signal, and the electrical interlock which prohibits an error code gener-ation when more than one key is depressed.
CONCLUSION
The solid state keyboard uses a new switching concept which capitalizes on the inherent reliability and low
cost of integrated circuits. The output of this device is compatible with the integrated circuits used in com-puters.
The keyboard is deliberately made modular so that it can be adapted to special key formats and codes. It provides an electronic interlock instead of the usual mechanical one, and as a result allows higher speed operation.
¥l}>ile the keyboard is different in TIli:my :respects, it has maintained those industry standards which have been substantiated by human factor studies such as key stroke and force, key loea tion, and the key layout in the touch typing area.
ACKNOWLEDG MENTS
The development of the solid state keyboard has been possible through the enthusiastic support and dedicated efforts of many people in our respective organizations.
We could not hope to fairly cite individual contributions within acceptable space limits here. We also appreciate the consultation provided by other research and engi-neering groups in our Company.
REFERENCES
R L DEININGER
Human factors engineering studies of the design and use
Solid State Keyboard 159
of pushbutton telephone sets
BSTJ Vol XXXIX No 4 995-1012 July 1968 2 R L DEININGER
Desirable push-button characteristics
IRE Transactions on Human Factors in Blectronics March 1960
:3 H M BOWEN
Rational design jor control: Man communicating to machine, Industrial design Vol XI No 5 51-59 May 1964
4 R D KI~CAID
Human factors design recommendations for touch operated keyboards
Report 12091-FR Honeywell Systems and Research Center January 1969
5 A C BEER
The Hall effect and related phenomena
Solid State Electronics Pergamon Press Vol 9 339-351 6 A C BEER
The Hall effect
International Science and Technology December 1966 7 0 N TUFTE E L STELZER
Magnetoresistance in heavily doped N-Type silicon Phys Rev Vol 139 No 1A A-265-A-271 July 5 1965 8 J G LINVILL J. F GIBBONS
Transistors and active circuits
McGraw-Hill Book Co New York 1961
9 R M WARNER JR J N FORDEMWALT (Editors) Integrated circuits
McGraw-Hill Book Co New York 132-149 1965 10 J T MAUPIN
The control characteristic oj current switching logic stages Honeywell Corporate Research Center Memorandum HR 63-37 July 1963