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Heathkit
Page 59
Refer to the Schematic Diagram (Illustration Booklet,
Page 19) while you read this "Circuit Description."
LOGIC SWITCHES
Switch A-A controls a latching flip-flop made up
of sections A and B of U106. When switch SW105
is in the A position, pin 1 is low. This produces
a high at pins 3 and 4. Pin 5 is also high through
R145. This makes a low at pin 6. When SW105 is
in the A position, a low is at pin 5. This forces pins
6 and 2 high. With highs at pins 1 and 2, pins 3
and 4 go low and the outputs A and A have changed
State.
Switch B-B operates the same as switch A-A.
BINARY DATA SECTION
The eight-section data switch has one side of all
switches
connected
to ground. The other side of
each section has a 4700 ohm pull-up resistor to the
5 V power supply. The connectors below the switch
provide convenient connection for two wires to each
switch section. With a switch in the lower (closed)
position, the associated terminal will provide a logic
0 level (ground). In the up (open) position the level
will be logic 1. The switch sections are numbered
0 through 7 from right to left.
LOGIC INDICATORS
input terminal to ground to hold the input at logic
0 when no connection is made to the terminals. Each
buffer output is connected through an LED and a
180 ohm current-limiting resistor to ground. When
the inputs to the buffer are logic 0, the outputs are
also 0 and the LED is off. When the input rises to
logic 1, the output also rises to logic 1 and lights
the LED.
The three functions of the generator (sine, square,
and triangle) are produced by U101; the square wave
is present at pin 11. It is fed to U103 where it is
buffered and inverted. Pin 2 of U101 has the sine
and triangle waveforms present. These waveforms
are selected by switch SW101.
The frequency of U101 is determined by capacitors
C106, C107, C108, C109, C111, and resistors R110,
R111, and R112. The pulse width output of U102
is determined by resistor R113 and capacitor C113,
C114, C115, C116, and C117.
PULSE GENERATOR
The signal from pin 11 of U101 is inverted by U103
and fed to multivibrator U102. The pulse width is
determined
by the selection
of capacitors
U113
through C117.
NOTE:
The frequency generator must be set to a
period greater than the pulse generator (P = 1/F).
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