A solid state turn coordinator display which employs light emitting diodes (LED's) as the display medium was developed to demonstrate the feasibility of such displays for aircraft applications. The input to the display is supplied by a fluidic inertial rate sensor used in an aircraft wing leveler system. The display is composed of the LED radial display face and the electronics necessary to address and drive the individual lines of LED's. Three levels of brightness are provided to compensate for the different amounts of ambient light present in the cockpit

Crouch, R. K.

Kelly, W. L., IV

Meredith, B. D.

English

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iN A S A TECHNICAL	 NASA TM X• 72782
MEMORANDUM
(NASA-TM-X-72 7 82) SOLID-STATE TUFN
COORDINATOR DISPLAY (NASA) 16 p HC
	
	
OCSCLOIDN
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SOLID-STATE TURN COORDINATOR DISPLAY
a
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Z	 By Barry D. Meredith, Roger K. Crouch,
and W. Lane Kelly, IV
N76-32186
Unclas
G3/06 04076
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This Informal documentatio n medium is used to provide accelerated or
special release of technical information to selected users. The contents
may not meet NASA formal editing and publication standards, may be re-
vised. or may be incorporated in another publication.
l	 AA
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 	 ^11^131^,
LANGLEY RESEARCH (ENTER,, HAMPTON, VIRGINIA 23665
RCT 1976 r
1 ryA^4	 r
^., ^► Omit;'
1. Report No.
	 I 2. Government Accession No.
_NASA TM X-72782
4. Title end Subtitle
3. Recipient's Catalog No
5. Report Date
August 1975
6 Pirtorminy Organvation Cade
d Perturminy Orymtzatton Report No.
1C 'W xk Unit No.
11 t,ontract or (,rant No.
_	 13. Type of Rvpurt and Pertoa Covered
Technical Memorandum
1Sponsor.ny A.tency Code
Solid-State Turn Coordinator Display
7 A uthor(sl
Barry D. Meredith, Roger K. Crouch, and
W. L. Kelly, IV
9 Performing Organization N.,me dnd Address
NASA-Langley Research Center
Langley Station
Hampton, VA 23665
12, Spunsurtng Ayerei 'Jame aid A-Wit-ss
National Aeronautics & Space Administration
Washington, DC 20546
1:) u oen-Ohwr, Notes
t
A solid state turn coordinator display which employs light-emitting diodes (LED's)
as the display medium has been developed to demonstrate the feasibility of such
displays for aircraft applications.
The input to the display is supplied by a fluidic inertial rate sensor used in
an aircraft wing leveler system.
The display is composed of the LED radial display face and the electronics
necessary to address and drive the individual i;nes of LED's.
Three levels of brightness are proviaed to compensate for the different amounts
of ambient light present -in the cockpit. Although the techniques described in
this report were used to construct a turn coordinator display, they coulc also
be used in the construction of more complex instruments.
I
11 Key Words ;5u9ges1[t ,J Ly Author(s))	 1d Distr,h..tn.t. ";tate veil
Displays,
LED's
	
Unclassified - Unlimited
19 Security Classif. tot this report'
	 20 Security Classif (of this ledge) 	 21 NO of P,Iyes	 2.' I
Unclassified	 I	 Unclassified	 14
	
45.25
Ft sale by the National Technical Information Service, Springfield, Virginia 22161
1SOLID-STATE TURN COORDINATOR DISPLAY
By Barry D. Meredith, Roger K. Crouch,
and W. Lane Kelly, IV
SUMMARY
A solid-state turn coordinator display which employs light-emitting-
diodes (LED's) as the display medium has been developed at Langley Research
Center to demonstrate the feasibility of such displays for aircraft
applications. The input signal to the turn coordinator display is supplied
by a fluidic inertial rate sensor. The display is composed of the LED
radial display face and the electronics necessary to address and drive the
individual lines of LED's. Three levels of brightness are provided to
compensate for the different amounts of ambient light present in the aircraft
cockpit. Although the techniques described in this report were used to
construct a turn coordinator display, they ccuic -: 1-s o be used in the
construction of more complex aircraft displays.
INTRODUCTION
The objective of the effort described in this report was to
demonstrate the feasibility of the design and construction of solid-
state aircraft displays employing light-emitting diodes (LED) as their
display medium. The solid-state turn coordinator display was developed for
this purpose. It complements a fluidic inertial rate sensor that was
adapted for use in an aircraft wing leveler system (ref. 1) at Langley
Research Center. The turn coordinator display provides the pilot with a
visual indication of the roll and yaw rate of his aircraft. Mechanical
turn coordinator displays presently in use are simple and reliable
I'	 devices. However, the technique employed it the development of the
solid-state LED display can be expanded to applications beyond the capability
of mechanical instruments. The solid-state turn coordinator display also
offers three levels of brightness to compensate for the different amounts
of ambient light present in the aircraft cockpit.
SIGNAL PROCESSING
Display Input Signal
The analog input signal to the solid state-turn coordinator display
is generated by a fluidic inertial rate sensor. This sensor consists
basically of two self-heated thermistors in a bridge circuit with a laminar
jet of air directed between each (ref. 1). When the device is suhject to
an angular rotation, the inertial properties of the jet causes it to be
deflected as shown in figure 1. This results in unequal thermistor
2
temperatures, and an analog difference voltage appears at the output of
the bridge circuit. This output voltage varies from +0.1 to -0.1 volts,
and since the sensor is tilted with respect to the longitudinal axis of
.	 the airplane, is proportional to both yaw and roll rate. The fluidic sensor
output signal is used to drive the turn coordinator display as well as
the wing leveler system.
Address Electronics
The initial stage of electronics (figure 2) in the solid-state
turn coordinator display is an operational amplifier which amplifies the
analog output of the fluidic sensor from 10.1V to 13.0 V. This amplified
voltage is the input to a analog-to-digital (A/D) converter, whose digital
signal goes to a decoder where it is decoded into one of 20 mutually
exclusive outputs. The decoded output is then inverted for compatability
with the LED current drivers.
LED Drive Circuitry
The LED current drivers consist of 20 transistors with a single
line of 10 LED's in the emitter circuit of each transistor (figure 3).
When the decoded pulse biases the selected transistor ON, drive current
is allowed to flow through the transistor and LED's to ground. This drive
current has a control circuit which determines the current pulse timing and
duty cycle. The control circuit is a one-shot oscillator whose output is
fed to the base of a transistor Qx (figure 4). This transistor allows
current to flow to the selected drive transistor; the length of time t"
current flows depends on the one-shot oscillator output pulse wi,'th. To
control pulse timing, the status pulse from the A/D converter is jt`zed.
The status pulse triggers the oscillator only when the output - the
3
converter is locked into its true data levels (fig. 5). -,'heref:,re, during
the A!D conversion interval,  erroneousi gn i s o nc-: ._; _ _ .--t  t 6.. e current
driver outputs.
By switching between three capacitors of different valaes in the one-
shot oscillator's RC network, the duty cycle of the one-shot output pulse
is varied (fig. 6). This change in pulse width varies in length of time
the control transitor is activated, thus affecting the average drive
current to the LED's. Since the average intensity of the LED's is
proportional to the drive current, three different display intensities
are obtained.
LED RADIAL DISPLAY
To complement the solid-state electronics section of the turn coordinator
display, an appropriate display face was desired. Therefore, the display
medium utilizes one of the more promising tecnnologies currently available --
light-emitting diodes (LED's). T;:e diodes are di;fused GaAsP bars, C.25 mm
wide x 1.9 mm long x 0.3 mm thick, from Bowna r .anada, Ltd. Co;':_ary
specifications show the peak emission to be a,.^rLximateiy 6:00 r, w;th a
brightness of abGat 1 5_0 ft-L for 10 ma of c;:rren7.
The LED's .:ere mounted or a copper disc 6.5 cm in diameter.
Initially, the disc was exposed to sulfur f,.:.:e<_ .rcducinc ccoPer sulfide
which blackened the surface. Then 22 ^rooveswe°e cut a',ong diameters,
with an angular separation of 5°. Each groove was approximately 0.5 mm
wide ana 0.3 mm deep. A hole 2.4 cm in 	 was cut	 the center
of the disc to pr^'ride a feedthreugh for the LED power -lends. -he LED's
were metallized by the manufacturer which enabled them to be mo.-.-ad :n the
w
OPIGINAL PAGE IS
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I
grooves of the disc using a conductive epoxy. Contacts to the top rf the
diodes were made by a ball-border using 50SAm gold wire. Since no o-.tidal
coupling optimization was performed, that is, using elliptical reflectors
or diffuse epoxies, fiva dicdes were mounted in each radial portion of tre
grooves (fig. 7). Twenty grooves were used, making a total of 200 LED's ;r
the display. Finally, the display was covered with a Wratten filter #29 to
decrease ambient light reflections and mounted with the electronics in an
aircraft instrument case (fig. 8).
POSSIBLE DIPSLAY IMPROVEMENTS
The original display developed at Langley Research Center is a
prototype which could be improved with a minimal manufacturing e•,fort.
For instance, through efficient circuit board layout and packaging, -Ka
size of the unit could be reduced by a factor of two.
Also, it would require very little effort in the manufacturing
process to cut the grooves of,,-the copper disc in elliptical shapes;
plate the grooves with a highly reflective coating; and after mounting
the diudes, fill the grooves with an epoxy which has an index of refr..c. ^.
matching that of GaAsP. These procedures would increase the optica.
coupling to such an extent that each radial segment would require or!
two LED's, thus reducing the power requirement of the dicdes by 60 pe.
CONCLUDING REMARKS
A solid-state turn coordinator display employing lig-..-emitting
diodes has been developed to demonstrate the feasibility of s6-.n dis
for aircraft applications. It interfaces with the fluidic inertial ra
5	
QiGINAL PAGE IS
)F POOR QUALITY
sensor which was adapted at Langley Research Center for use in a wing
leveler system. The solid-state display was not developed to compete
with the present mechanical turn coordinator display but rather to
investigate techniques that could be utilized in the develpment of more
complex aircraft instrumentation.
6
REFERENCES
1. Garner, H. Douglas; and Poole, Harold E.: Development and Flight
Tests of a Gyro-Less Wing Leveler and N rec4ional Autcpilot.
NASA TN D-1460, 1974.
7
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Figure 4. - Drive C_irrvnt Control Circuit
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Solid-state turn coordinator display

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