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THE DECADE COUNTER
The 4017 IC is a 5 stage divide by 10 counter. Figure 2 shows a diagram of this IC. This
IC has 10 outputs and a clear input. Only one of the 10 outputs will be high at any given
time. The other 9 will be low. Let’s assume that output 1 is high. If a pulse is fed into the
clock input, output 1 will go low and output 2 will go high. Each clock pulse will move the
output one position. Connect an LED to the output, it will light only when the output goes
high. It is obvious that when the clock is running, the LEDs will flash on and off with the
speed of the clock. When the clock stops, only one LED will be lit.
In this design, 8 LEDs are used per IC, but the counter has 10 outputs. If the clock stops
at an output without an LED, nothing will light. To prevent this, the 4017 IC is reset after
hitting the 8th output. This is simply done by tying the 9th output to the clear pin (pin 9
and pin 15 shorted together).
THE LIGHT EMITTING DIODES (LED)
The operation of the LED is very simple. When current flows through the LED, it will emit
light. Note that the LED is connected between an IC output and ground through a resistor. When the IC output goes high,
the LED will light. The resistor limits the current so that the LED will not be damaged.
OSCILLATORS
The Love Tester uses two oscillators. The first oscillator produces a frequency of about 20 hertz (cycles) and the other
produces a frequency of about 2000 hertz. Figure 3 shows the basic oscillator
circuit. The 4011 integrated circuit (IC) contains four two-input NAND gates. Two
of these NAND gates are needed to form an oscillator. Feed back for this
oscillator is via capacitor C2 and resistors R4 and R5. These elements
determine the frequency of oscillation. Both IC1 and IC2 act as inverters, that
is, when the input is low, the output is high. As long as pin 13 of IC1 is high, the
circuit will oscillate. If pin 13 is brought low, the circuit will stop oscillating.
The second oscillator is similar to the one described except for a difference in its
frequency controlling components, capacitor C1 and resistors R2 and R3. C1
and R2 are smaller values causing the oscillator to oscillate at a much higher frequency. Pin 6 of the first NAND gate is
brought high at a 20 cycles rate. This causes the second oscillation to be chopped up at the first oscillation frequency rate
as shown in Figure 4. This combination produces the unusual sound heard from the buzzer.
BUZZER
The Love Tester buzzer consists of a piezoelectric material on a metal base. When a voltage is applied to piezoelectric
material, its dimensions change. The buzzer is connected to the 2kHz oscillator. When the oscillator runs, the changing
dimensions to the piezoelectric buzzer act like the cone of a speaker to set up sound waves.
TIMER
Timer 1 is made up of capacitor C3 and R6. Timer 2 is made up of capacitor C4 and R7 (see schematic diagram). When
S1 is pushed, both capacitors charge up to 9 volts and the oscillators run. When the switch is released, capacitor C3
discharges through resistor R6 and capacitor C4 discharges through resistor R7 and the base of Q1.
Note that C3 is tied to pin 13 of the 4011 IC. Thus, when capacitor C3 loses its charge, the circuit stops oscillating. The
buzzer stops and a single LED remains lit. After a minute or two, C4 loses its charge and removes the base current from
Q1. Q1 is in the ground return path of the LEDs and both ICs. Thus, when Q1 is turned off, the LED goes out. Only a very
small leakage current is then drawn from the battery. This current is so small that no ON/OFF switch is required.
Figure 2
3
2
4
7
10
1
5
6
9
11
12
VDD - Pin 16
VSS - Pin 8
Block Diagram
Figure 3
Figure 4
IC2
R5 R4
C2
+V
Pin 13 IC1
4011 IC
15
14
1
Q0
Q1
Q2
Q3
Q4
Q5
Q6
Q7
Q8
Q9
COUT
Clock
Clock
Enable
Reset
