Radio Shack VoxBox TRS-80 User manual

I
1
m
»;
m
i
i
i
I
i
TRS-80
TM
RECOGNITION
Catalog Number 26-1181
tZcMIlO /fitick tws-so VOXBQX
p'II|Mll Mll lM||li|"i™wi<^4'ilifllfifo^i''^^ wss
CUSTOM MANUFACTURED FOR RADIO SHACK^A DIVISION OF TANDY CORPORATION

1. Introduction
This manual provides the serviceman information necessary to repair the Radio Shack
TRS-80 VOXBOX Speech Recognition peripheral. The hardware involved in the device is
fairly simple; most of the complex task of speech recognition is accomplished by the
TRS-80 computer, which executes asoftware algorithm on the raw data provided by the
speech recognition hardware. The hardware itself simply extracts four bits of information
from the speech waveform and presents it to the computer. The recognition program
samples this data approximately every 10 ms.
In addition, two BASIC test programs are available to help debug the board. The first
program tests the board by training and recognizing the ten digits zero through nine. The
second program plots the information gathered by the board on the video monitor
where it may be compared to known patterns to help isolate the problem.

2. Troubleshooting The VOXBOX
This product is easy to troubleshoot. It has aserial analog signal path which starts at the
microphone and terminates at the voltage comparators. Thus the signal may be
traced from beginning to end to determine where the problem lies. Use the test programs to
help isolate the trouble.
Test equipment required is as follows:
•TRS-80 computer with Level 11 BASIC
•Oscilloscope
There are no adjustments to be made.
Test Programs
The first step in troubleshooting the board is to run the programs to verify improper
operation. Listings for Program 1and Program 2are contained in this section.
PROGRAM 1
Load the speech assembly language routines using the "system" command and load the
BASIC program "Test 1". Run the program, train the system on the ten digits by speaking
clearly, and try the unit out. The unit should respond with at least 80% to 90% correct
results. If the unit does not operate at all, go to the hardware tests in Section 2-B,
and particularly inspect the power supply, mike preamp, and addressing logic. If the unit
responds but operates poorly, load the second BASIC test program "Test 2".
PROGRAM 2
Run the second program and say the word "six" loudly and clearly. You should see roughly the
same shaped plots as shown in Figure 1.
If any of these lines are constant across the screen with no variation at all, then the
corresponding area of the circuitry is at fault.
The top line is aplot of low band energy, which corresponds to the rectifier/ averager output
from low band on the block diagram and is the output from IC4-1 on the schematic.
The second line from the top is high band energy, from the high band rectifier/ averager on the
block diagram, or from IC4-2 on the schematic.
The next line is the high band zero-crossing rate, from the high band zero-crossing detector on
the block diagram, or from IC4-1 3on the schematic. Finally, the bottom line is the low
band zero-crossing rate, from the low band zero-crossing detector on the block
diagram, or from IC4-14 on the schematic.
Test Program 1can be run, ifdesired, before disassembling the unit to verify customer trouble
complaints.
Disassembly Procedure
Place the unit upside down on aclean surface and remove the 6screws which hold the top and
bottom half of the plastic enclosure together. Remove the board from the box by lifting
it out and place the board on aclean non-conducting surface.

VOXBOX BOARD (IN BOX) TOP COVER REMOVED
FIGURE 1
-3-

L>"AMPLITUDES'
>"FREQUENCIES'
TYPICAL PLOT OF WORD "6"
AS SEEN ON TRS-80 VIDEO DISPLAY
FIGURE 2
-4-

TKST PROGRAM 1
DIGITS
10 REM SET UP CALLING PARAMETERS
20 REM MS=MEMORY SIZE IN K-BYTES
30 AD=112
40 GOTO 80
80 POKE 16526,6
90 POKE 16527, AD
100 X=USR(0)
200 REM TRAIN
210 REM TR= INDEX; W$=STRING ARRAY
220 DIM W$ (32)
230 W$ (0)="0"
240 W$ (1)="1"
250 W$ (2)="2"
260 W$(3) ="3"
270 W$ (4)="4"
280 W$ (5) ="5"
290 W$ (6) ="6"
300 W$ (7) ="7"
310 W$ (8) ="8"
320 W$ (9) ="9"
330 W$ (10) ="10"
340 FOR TR=0 TO 10
350 PRINT "SAY. .." ;W$ (TR)
360 GOSUB 1000: REM TRAIN
370 NEXT TR
400 REM GET VOICE INPUT
410 POKE 16 526,3
420 POKE 16527, AD
430 PRINT "SPEAK. .
.
"
440 X=USR(0):REM CALL RECOGNITION
450 W=PEEK (TX)
460 IF W>31 THEN GOTO 500
470 PRINT "YOU SAID ";W$(W)
480 GOSUB 900: REM DELAY
490 GOTO 400
500 REM ERROR
510 PRINT "PLEASE REPEAT THAT"
520 GOSUB 900: REM DELAY
530 GOTO 400
900 REM DELAY FOR BETTER USER INTERACTION
910 FOR 1=1 TO 300
920 NEXT I
930 RETURN
1000 REM CALL TRAINING SUBROUTINE
1010 TX-256*AD+1018
1020 if TX >32767 THEN TX =TX-65536

TEST PROGRAM 1(Continued)
1030 POKE 16526,0
1040 POKE 16527, AD
1050 POKE TX,TR :REM PASS TRAINING INDEX TO SBR
1060 X=USR(0)
1070 IF Peek(TX) <> THEN GO TO 1090
1080 RETURN
1090 PRINT "ERROR -PLEASE REPEAT"
1100 GOTO 1000
TEST PROGRAM 2
•PLOT''
NOTE: Same program as in User Manual —on User Cassette
10 :IF PEEK (-4095) =12 THEN 60
20 :IF PEEK (-20479=12 THEN 70
30 :IF PEEK (28673) =12 THEN 80
40 ]PRINT "ERROR: VOX BOX SOFTWARE NOI1LOADED"
50 ]3ND
60 ]R1=240:B1=-3078:L1=-2411:B2==-3041: GOTO 90
70 ]*1=176 :Bl=-19 46 2:L1=- 18795:132=-19425:GOTO
80 ]R1=112:B1=29690:L1=303 57:B2==29727: GOTO 90
90 (:ls
100 PRINT 350, "SPEAK. .."
;
110 POKE B1,0
120 POKE 16526,0
130 POKE 16527, Rl
140 X=USR(0)
150 CLS
160 L=PEEK(L1)
165 PRINTS 114 ,"LEN=" ;L
;
170 B=B2
180 FOR 1=10 TO L+10
190 IF PEEK(B)=0 THEN X=l ELSE X=0
200 SET (I,X)
210 IF PEEK(B+1)=0 THEN X==1 ELSE X=0
220 SET(I,X+4)
230 SET(I,47-PEEK(B+2)/4)
240 SET(I,4 7-PEEK(B+3)/4)
250 B=B+4
260 NEXT I
270 GOTO 100
280 END
90
-6-

Power Supply
Plug the battery eliminator into a120 VAC outlet and into the miniature power jack on the
board and check the output at the miniature powerjack for DC output using the
oscilloscope. The minimum instantaneous voltage frojii the battery eliminator, the lowest
voltage point on its output waveform, must be 14.5 volts or greater.
If the output dips below 14.5 volts, the analog circuitry will be affected by noise on the internal
power supply lines as the voltage drops out of regulation. Change battery eliminator
to see if this cures the problem. If not. the problem may be the voltage regulator circuits. Test
the resultant voltages on the PC board as shown in Table 1.
Voltage
TABLE
Test Point
IC6 Pin 4
1C1 Pin 14
IC6 Pin 3
1
Tolerance
59 (+600mv)
59 (+250mv)
5^ (±300mv)
Ripple
+12
+5
+6
25 mv
50 mv
10 mv
The +12V is generated by a78 L12 regulator, the+5V by a78M05 regulator, and the +6Vfrom a
zener diode dropping network on the +12V supply. In particular, the +12V supply
should be free from noise in the 0-10 KHz band.
Microphone Preamp
Insert the microphone into its mating connector. Close the push-to-talk switch, speak into the
microphone and observe the preamp output IC6, Pin 7. The output should swing
above and below the resting level of 6V. If no signal is present, test for output at the first
preamp stage IC6, Pin 1. If the "no signal" output level is not 6V, check for the 6V
reference level at amplifier inputs IC6-3and IC6-5. If no signal from the first stage of the
preamp, test the microphone output at the DIN connector for 10mvto40mv
output when speaking loudly or whistling.
Filters
Check the high and low band filters for output at IC5. Pin 7. the last stages, and if not present,
check the first stage. The output should be 6Vwith no signal input, and should swing
above and below with signal input. Table 2summarizes these tests.
TABLE 2
Filter Stage
Last
Test Point
1C5-7
No Signal Level
Low Band 6V
Low Band First IC5-1 6V
High Band Last 1C6-14 6V
High Band First IC6-8 6V

Zero-Crossing Detectors
The zero-crossing detectors outputs should be volts with no input and swing to 5volts when
the filter output swings much below its rest level of 6volts. Whistling into the
microphone should produce asquare wave output whose period varies with the pitch
(frequency) of the whistle. Table 3summarizes this test.
TABLE 3
Signal
Input
(at MIC.)
High Band Low Band
Output
IC4-14
Input
IC4-8
Input
IC4-9
Output
IC4-13
Input
IC4-10
Input
IC4-11
Whistle Square Waves
to +5V
at whistle
frequency
Sine Waves
Swinging
Above &Below
+6V
DC Voltage
Slightly Less
Than 6Volt
Reference at
IC5-5
Square Waves
to +5V Sine Waves
Swinging
Above &Below
6V
DC Voltage
Slightly Less
Than 6Volt
Reference at
IC6-12
None Random
Square Waves
6VDC Same as
above
Random
Square Waves
6VDC Same as
above
Rectifier/ Averagers
The comparator outputs should sit at volts with no signal and go to +5 volts with signal into
the system. The amplifier outputs should sit at 6volts with no signal input and sit at a
steady state voltage less than 6volts for steady state sounds (Ahhh etc.). Table 4sum-
marizes the results.
Low Band
Amplifier 1C5-8
High Band
Amplifier IC5-14
Low Band
Comparator 1C4-1
High Band
Comparator 1C4-2
TABLE 4
Signal Input
to 5volts
to 5volts
5volts
5volts
No Signal Input
6volts
6volts
volts
volts
-8-

Address Decoding
This peripheral decodes address port AFIi (175io), Whenever this address is accessed by the
processor via an input instruction the data bus buffers are enabled. 1his mav be
detected statically by disconnecting the board from the TRS-80 computer and grounding edge
connector pins 38( A6) 3l( A4)and 19(in). 1C2 pins 1and 13 should goto +4volts as a
result enabling the bus butters with the 4volt signal at 1(3 pins i,4. 10, and 13. Alternative lv,
the address logic may be checked dynamically by entering ashort assembly language
routine with the IBl (j program This program does an input from Port AFH and loops back
and does it overand overagam. Positive pulses should be seen at 1C2 pins 1and 13.
and at IC3 pins 1,4.8, and 13. I:sing the "VI" memor\ till function ot IBUG. choose amemory
area and enter the following program:
(Address) DB
AF
C3
(Address)
For example, if the program is chosen to reside at 7000 H. the steps would be:
M7000 DB
AF
C3
00
70
To execute the program at 7000H, type J7000, |jg£|£3£J
Assembly Procedure
Place the board component side up into the bottom half of the plastic box so that the three
mounting holes on the board line up with the shoulders of the posts in the box.
Arrange the cable through two 90 degree bends and place the existing cable into the guide slot
and cable clamp built into the box. Carefully place the top of the box over the bottom
half and, holding the box securely, turn the box upsidedownand replace the 6screws holding
the box together.
Run the digit test program (#1) to verify correct operation of the board.

3. Theory of Operation
This section provides the theory of operation of the speech recognition hardware functional
blocks, as shown in block diagram Figure 3.
Microphone
The first element in the signal chain is the microphone, adynamic microphone with a
push-to-talk switch. While there are several circuits in the microphone, the only circuit used is
the audio circuit, which delivers the 1mv —40 mv signal from the microphone when the
switch is closed and is an open circuit when the switch is open or released.
Microphone Preamp
The microphone preamp amplifies and frequency compensates the microphone signal before
the signal is passed to the bandpass filters. The input from the microphone is terminated
in a1Kresistor to ground which keeps the microphone input grounded when the
microphone switch is released. The first stage of the microphone preamp "pre-emphasizes"
the speech input, amplifying higher frequencies more than lower frequencies, with the
rate of increase being 6DB/ octave. This compensates for vocal tract characteristics, which
produce less energy at higher frequencies than at lower frequencies.
This pre-emphasis continues up to about 1.5 KHz after which the preamp output rolls off, or
decreases, at arate of 12 DB octave. The second stage of the microphone preamp
provides additional gain. The microphone preamp amplifies the 10 —40 millivolt microphone
signal and produces asignal of 1to 10 volts peak to peak output. Since all the analog cir-
cuitry operates from asingle +12Vsupply, the output of the microphone preamp is
biased for ano-signal output of about 6V, and swings above and below this rest level. This
amplified and frequency compensated signal is then applied to the inputs of the two bandpass
filters.
Filters
The two bandpass filters are each implemented as a low pass filter followed by ahigh pass
filter. The low band filter formed by IC2-1 and IC2-7 has apassband of 150 Hz to 900 Hz. The
high band filter formed by IC1-8 and IC 1-14has apassband of 1KHz to about 4KHz.
The outputs of the filter stages are biased to arest level of about 6V, through the application
of the 6V reference level to the non-inverting inputs of all the amplifiers. The output of
each filter stage is sine waves whose frequencies fall within the passband of the associated filter.
The frequencies of the sinewaves are the same as the frequencies contained in the input
signal from the microphone, and the amplitude of the sinewaves is proportional to
the amplitude of the signals from the microphone, modified by the frequency shaping in
the microphone preamp. The output of each filter is applied to azero-crossing detector and a
rectifier averager circuit.
-10-

HIGH BAND
FILTER
MIKE
PREAMP
ADDRESS .
BUS
AMPLITUDE
DETECTION
ZERO CROSSING
DETECTOR BUS
DRIVERS
LOW BAND AVERAGER AMPLITUDE
DETECTION
FILTER
ZERO CROSSING
DETECTOR
1,
ADDRESS
DECODING BUS
DRIVERS
•DATA IN BUS
VOXBOX BLOCK DIAGRAM
FIGURE 3
-11

Zero Crossing Detector
1he zero crossing detector is acomparator which compares the filter output with afixed
voltage and generates a+5 volt output when the filter output is less than the fixed
voltage, and azero volt output when the filter output is greater than the fixed voltage. The
fixed voltage is the 6Vreference voltage, so that with no signal input the detector output
is arandom square wave pattern generated by random low level noise in the circuitry. When a
slight signal comes from the filter output, the detector output will switch from zero to +5 volts
and back to zero as the filter output swings above and below the fixed voltage.
Rectifier/ Averager
The output of each filter also drives an associated rectifier averager stage. The input to the
circuit is through adiode. Since both the inverting and non-inverting inputs of the
amplifier are at the 6volt reference, the diode will conduct only when the filter output is at
least one diode drop above its rest output of 6volts. The diode thus rectifies the signal and the
associated amplifier inverts the signal and averages it with a20 Hz low pass filter. The
output of the rectifier averager is thus the 6volt reference in the absence of any input signal,
and moves toward ground when an input signal is applied. The higher the amplitude of
the input, the closer the output is to ground. The output of the rectifier/ averager
stage is applied to the negative input of avoltage comparator whose positive input is afixed
voltage just slightly less than the 6volt reference. The normal comparator output is thus
zero volts. When asmall amount of speech energy is amplified, filtered, and rectified, the out-
put of the rectifier stage trips the comparator producing a5volt output from the
comparator. This signal indicates speech energy is being produced in the bandwidth of its
associated filter. This signal from each of the rectifier averages is fed to abus driver,
along with the two zero crossing detector outputs where it is made available to the processor.
Address Decoding
From the viewpoint of the TRS-80, the speech input peripheral is asingle input port at address
AFH (175 decimal). Whenever this address is accessed with an input instruction, the
peripheral places its data on the computer data bus in the format shown in Figure 4.
Power Supply and Regulators
The speech input peripheral uses 2voltages internally, a+5 volt supply for the digital circuitry
and a+12volt supply for the analog circuitry. These voltages are regulated internally
using the raw DC voltage supplied by the battery eliminator which plugs into the wall.
D7-D4 D3 D2 D1 DO
NOT USED HIGH BAND
AMPLITUDE HIGH BANK
ZERO CROSSING LOW BAND
ZERO CROSSING LOW BAND
ENERGY
1=ENERGY
0=NO ENERGY 1=ENERGY
0=NO ENERGY
FIGURE 4
-12-

VOXBOX Technical Specifications
General
Function:
Type:
Vocabulary Size:
Connects to:
Method of Connection:
Word Definition:
Equipment Required:
Memory Requirements:
Peripheral Device
Address Used:
Inputs:
Power:
Logic Signals:
Voice:
Word Recognition for Data Input and
Control.
Isolated-Word, Speaker Trained
32 Words
TRS-80. or
TRS-80 Expansion Interface
Cable provided for connection.
Word or phrase length 0.1 to 1.5 sec.
Beginning of word identified by 0.1 sec. of
continuous speech.
End of word identified by first interval of
silence at least 0. 1sec. which follows
detection of beginning of word.
TRS-80 with Level II Basic and at least 16K
RAM. May be used with other peripherals
and more capable versions of TRS-80
system.
4096 bytes RAM reserved at the high end
of user memory.
I/O PORT AF HEX (175 DEC)
120 VAC, 50-60 Hz, 0.1 Amp via separate
15 VDC power pack (included).
TRS-80 peripheral bus
Push-to-Talk microphone (included)
Physical Specifications
Temperature:
Humidity:
Size:
Weight (shipping):
32°F-110°F Operating
-40°F-160°F Storage
0-95% Non-condensing
iy
4"H X7"WX 5'/
2"D
(5 cm X20 cm X14 cm)
2lbs (1 kg)
-13-

wo
ZLU
Old UJ3S
CCOWl-Z
<Q3XO
OUJflOlUO
-14-

PARTS LIST
(Order from VOXBOX Manufacturer Using Reference Designator Preceded By "V")
Ref. No. Description RS Part Number MFR's Part Number
CAPACITORS
C1 Mylar 0.01,uF 25V ±10%
C2 Mica 100pF 25V ±10%
C3 NOT USED
C4 NOT USED
C5 Mylar 0.0047^F 25 V±10%
C6 Mylar 240pF 25V ±10%
C7 Mylar O.OIjuF 25V ±10%
C8 Mylar 0.022;uF 25 V±10%
C9 Mylar 0.01/iF 25V ±10%
C10 Mylar 0.01/iF 25V ±10%
C11 Tantalum 10juF 25 V±10%
C12 Tantalum 1juF 25V ±10%
C13 Tantalum 1;uF 25V ±10%
C14 Mylar 0.01 ^F 25 V±10%
C15 Mica 240pF 25V ±10%
C16 Mylar 0.0O22iiF 25 V±10%
C17 Mylar 0.0022 25 V±10%
C18 Mylar 0.00 IjuF 25 V±10%
C19 Mylar 0.01/xF 25V ±10%
C20 Ceramic 0.1|UF 25V +80,-20
RESISTORS
R1 Carbon Comp 1K1/4W 5%
R2 Carbon Comp 510K 1/4W 5%
R3 Carbon Comp 100K 1/4W 5%
R4 Carbon Comp 8.2K 1/4W 5%
R5 Carbon Comp 5.1K 1/4W 5%
R6 Carbon Comp 300K 1/4W 5%
R7 Carbon Comp 360 K1/4W 5%
R8 Carbon Comp 360 K1/4W 5%
R9 Carbon Comp 75 K1/4W 5%
R10 Carbon Comp 240K 1/4W 5%
R11 Carbon Comp 18K 1/4W 5%
R12 Carbon Comp 300 K1/4W 5%
R13 Carbon Comp 300K 1/4W 5%
R14 Carbon Comp 30 K1/4W 5%
R15 Carbon Comp 750K 1/4W 5%
R16 Carbon Comp 30K 1/4W 5%
R17 Carbon Comp 150 1/4W 5%
R18 Carbon Comp 10K 1/4W 5%
R19 Carbon Comp Jumper (0) 1/4W 5%
R20 Carbon Comp Jumper (0) 1/4W 5%
R21 Carbon Comp NOT USED 1/4W 5%
R22 Carbon Comp NOT USED 1/4W 5%
R23 Carbon Comp NOT USED 1/4W 5%
R24 Carbon Comp Jumper (0) 1/4W 5%
R25 Carbon Comp 130K 1/4W 5%
R26 Carbon Comp 3.3K 1/4W 5%
R27 Carbon Comp 130K 1/4W 5%
R28 Carbon Comp 3.3K 1/4W 5%
15-

Ref. No. Description RS Part Number MFR's Part Number
RESISTORS
R29 Carbon Comp 33K 1/4W 5%
R30 Carbon Comp 430K 1/4W 5%
R31 Carbon Comp 430K 1/4W 5%
R32 Carbon Comp 30K 1/4W 5%
R33 Carbon Comp 750K 1/4W 5%
R34 Carbon Comp 30K 1/4W 5%
R35 Carbon Comp 10K 1/4W 5%
R36 Carbon Comp 10K 1/4W 5%
R37 Carbon Comp 10K 1/4W 5%
R38 Carbon Comp 10K 1/4W 5%
R39 Carbon Comp 5.1K 1/4W 5%
INTEGRATED CIRCUITS &SEMICONDUCTORS
IC1 Integrated Circuit, Logic 74LS30
IC2 Integrated Circuit, Logic 74LS02
IC3 Integrated Circuit, Logic 74126
IC4 Integrated Circuit LM339
IC5 Integrated Circuit LM324
IC6 Integrated Circuit LM324
IC7 Power Regulator Circuit 78M05
IC8 Integrated Circuit 78L12
CR1 Diode IN752
CR2 Diode IN4148
CR3 Diode IN4148
CR4 Diode IN4148
MISCELLANEOUS
J1 Subminiature Phone Jack Imtronics HCY250
J2 DIN plug, Microphone Input SMKSI-3354
J3 Cable Assy
SI Power Switch Centralab
2KAB010000/132
T1 Power Unit, 15V
LA1 Radio Shack Label
PCB1 Printer Circuit Board
EN1 Molded Plastic Enclosure
M1 Microphone, Push To Talk 21-1172
PC1 CardBoard Packing Carbon
UM1 User Manual
SC1 4-24 x3/4" screws (Qty 6)
CT1 Cassette Tape #1, Lunar Lander/I nven. Demo
CT2 Cassette Tape #2, Voice Plot/SP48
CT3 Cassette Tape #3, SP16/SP48
-16-

3CR3)—
R14 |—
e
Qcio
f— R15
R16
_^i
u
CD OCD
Hw«
R12
^Wftsi
R9
R8
f;
>j.
R21 |
—
HR24 h-
—{R23 f—
I—}R20 |—ft Y«
HjllG—**
—|R18 |—~<CR2i>-
fe-|R17 |»NVllf
C12 C13 C11
-17-

APPENDIX D. Parts Circuit Diagrams
8-INPUT
POSITIVE-NAND GATES
74LS30
positive logic:
Y=ABCDEFGH
VCC NC HGNC NC Y
i\
^riiriirT^Tiriiriir
CDEFGND
QUADRUPLE 2-INPUT
POSITIVE-NOR GATES
74LS02
positive logic:
Y=A+B
Vcc 4Y 4b 4A 3Y 3B_ 3A
1Y 1A IB 2Y 2A 2B GND
QUADRUPLE BUS BUFFER GATES WITH THREE STATE OUTPUTS
74126
positive logic:
Y=A
Output is off (disabled) when Cis low.
VCC *C 4A 4Y 3C 3A 3Y
See page 6-33
>
1C 1A 1Y 2C 2A 2Y GND
SN54126U, W) SN74126(J,N)
SN54LS126 (J, W) SN74LS126 (J, N)
LM339 schematic and connection diagrams
_L-,
£} 35A(5)lOO„A (JJ)]S„A ()
-INPUT O-
W"^i^"M
TK
sv—
1
05 I•I06 -i -dt
Dual-ln-Line and Flat Package
OUTPUT 3OUTPUT 4GND INPUT 4' INPUT 4' INPUT 3* INPUT 3
13 112
DL<£
r<t;
2I34567
OUTPUT OUTPUT 2OUTPUT! V* INPUT 1" INPUT 1* INPUT 2" INPUT 2*
TOP VIEW
-18-