Figure 9 – Elenco Digital / Analog Trainer in Case User Manual
Page 11
-10-
The XR-2206 is comprised of four functional blocks,
a voltage controlled oscillator (VCO), an analog
multiplier & sine shaper, a unity gain buffer amplifier
and a set of current switches.
The VCO actually produces an output frequency
proportional to an input current. Across pins 5 and
6, a timing capacitor, is switched on to give 5 different
ranges of frequencies via COARSE FREQ. switch.
On pin 7, the FINE FREQ. ADJ. variable resistor
controls the actual frequency output. These two
components form the RC time constants for the
oscillator frequency.
The VCO produces a squarewave signal. This
squarewave is sent to a shaper and converted into a
sine wave.
THE LOGIC INDICATORS
There are eight logic indicators. Figure 9 shows the
circuit. It consists of a 74HC04 IC. When the input
is over 2.8V, the output of the IC will be low, drawing
current through the LED indicator. The 120 ohm
resistor limits the current in the LED to about 30mA.
100k
Ω
100k
Ω
120
Ω
74HC04
LED
5V
Figure 9
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