Avtech AV-1010-C-3MA Instructions Manual page 16

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Fig. 7
CLOCK MODULE
The clock module provides most of the AV-1010's timing
functions. The module can be triqqered by an internal
or an external trigger. If SW3 is in the EXT position,
pin 7 is grounded and the module will be triggered by
TTL pulses entering on pin 15, which connects to pin 4
of the threshold module. Also, when in the EXT mode,
the AV-1010 can be triggered by the SINGLE PULSE push
button (SW10). Each press triggers one pulse. The
normally open and normally closed terminals of the
switch are connected to pins 17 and 4, respectively.
The switch is debounced. When SW3 is in the INT
position, pin 7 has +5.8V on it and the internal
oscillator is enabled. The frequency of the oscillator
is controlled by the capacitance across pins 2 and 3 and
the voltage on pin 19. Different fixed capacitors,
corresponding to different ranges, are switched in by
the PRF RANGE switch (sw4) and the PRF FINE
potentiometer varies the frequency continuously by
varying the voltage on pin 19 between 0 and +5.8V. The
frequency can be varied between 10 Hz and 1 MHz.
The trigger pulse, whether internal or external, is then
split into two channels. The first channel is fed into
a' monostable multivibrator which produces a nearly
coincident pulse with a fixed, 50 ns pulse width. This
pulse is buffered and is available on pin 6.