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74-Series Chips
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Contents
Introduction
History: a computer from the catalogue
Lesson 0. Gates from transistors: for those who start from scratch
0.1. The idea: a transistor is a switch
0.2. Building
0.3. Check
Lesson 0 paste (Cmd+I)
Lesson 1. Logic in packages: 74HC00, 02, 04, 08, 32
1.1. The idea: a chip is a package with gates
1.2. The idea: free inputs go to ground
1.3. The idea: a latch from one chip
1.4. Building
1.5. Check
Lesson 1 paste (Cmd+I)
Lesson 2. Flip-flops in a package: 74HC74 and a frequency divider
2.1. The idea: a flip-flop with set and reset
2.2. The idea: six NANDs inside
2.3. The idea: a divider is a flip-flop that flips
2.4. Building
2.5. Check
Lesson 2 paste (Cmd+I)
Lesson 3. A counter in a package: 74HC390 and a stopwatch
3.1. The idea: ÷2 and ÷5 make ÷10
3.2. The idea: clocking on the fall
3.3. The idea: reset on a one
3.4. Building
3.5. Check
Lesson 3 paste (Cmd+I)
Lesson 4. A decoder in a package: 74HC138 and a running light
4.1. The idea: number → one wire
4.2. The idea: active 0
4.3. The idea: 4 → 16 from two 3 → 8
4.4. Building
4.5. Check
Lesson 4 paste (Cmd+I)
Lesson 5. A shift register: 74HC595 and 8 lamps over three wires
5.1. The idea: bits over one wire
5.2. The idea: a latch shows everything at once
5.3. The idea: the third state
5.4. Building
5.5. Check
Lesson 5 paste (Cmd+I)
Lesson 6. Bus buffers: 74HC244 and 74HC245
6.1. The idea: a bus and the third state
6.2. The idea: a buffer is a double inversion
6.3. The idea: both ways — two 74HC244
6.4. Building
6.5. Check
Lesson 6 paste (Cmd+I)
Lesson 7. An electronic dice
7.1. The idea: a counter to six
7.2. The idea: face number → dots
7.3. The idea: a fair roll
7.4. Building
7.5. Check
Lesson 7 paste (Cmd+I)
Summary
All the parts
Instructions in pictures
Lesson 3 in pictures
← Back to the lesson: Lesson 3. A counter in a package: 74HC390 and a stopwatch
3
Counter: 74HC390
and 74HC86 — a stopwatch 00–99
kh
HB-05
74HC86
74HC390
42
IN
14×
OUT
12×
XOR
4×
0
74HC04
1×
1
74HC02
1×
1
74HC08
2×
1
74HC74
4×
2
Hz
1×
0
1×
Q
Q
1×
4b
0
A
2×
1×
∞
Ctrl
+
G
74HC86
74HC390
© 2026 Daniil Khanin · khanin.info · HB-05
30
CANVAS
1
Delete
1Hz
CLK
Reset
Reset
CLR
CLK
Q0
Q1
Q2
Q3
4b
0
Q
2
Delete
74HC04
1A
CLR
2A
GND
3A
GND
4A
GND
5A
GND
6A
GND
1Y
nCLR
2Y
3Y
4Y
5Y
6Y
74HC74
1RD
nCLR
1D
Q0N
1CP
CLK
1SD
VCC
2SD
VCC
2CP
Q0N
2D
Q1N
2RD
nCLR
1Q
Q0
1QN
Q0N
2QN
Q1N
2Q
Q1
3
Delete
74HC74
1RD
nCLR
1D
Q2N
1CP
Q1N
1SD
VCC
2SD
VCC
2CP
Q2N
2D
Q3N
2RD
nCLR
1Q
Q2
1QN
Q2N
2QN
Q3N
2Q
Q3
© 2026 Daniil Khanin · khanin.info · HB-05
31
74HC86
4
IN
8×
OUT
4×
1A
1B
2A
2B
3A
3B
4A
4B
1Y
2Y
3Y
4Y
5
XOR
3×
0
9×
XOR
I0
1A
I1
1B
O0
1Y
XOR
I0
2A
I1
2B
O0
2Y
XOR
I0
3A
I1
3B
O0
3Y
6
XOR
1×
0
3×
XOR
I0
4A
I1
4B
O0
4Y
7
Ctrl
+
G
Library
…
Chip N
2×
Library
…
74HC86
Enter
74HC86
1A
1B
2A
2B
3A
3B
4A
4B
1Y
2Y
3Y
4Y
© 2026 Daniil Khanin · khanin.info · HB-05
32
74HC390
8
IN
6×
OUT
8×
1CP0
1MR
1CP1
2CP1
2MR
2CP0
1Q0
1Q1
1Q2
1Q3
2Q3
2Q2
2Q1
2Q0
9
74HC04
1×
1
12×
74HC04
1A
1CP0
2A
1CP1
3A
1MR
4A
2CP0
5A
2CP1
6A
2MR
1Y
1c0
2Y
1c1
3Y
1nMR
4Y
2c0
5Y
2c1
6Y
2nMR
10
74HC02
1×
1
10×
74HC02
1A
1Q1
1B
1Q3
2A
2Q1
2B
2Q3
3A
GND
3B
GND
4A
GND
4B
GND
1Y
1d1
2Y
2d1
3Y
4Y
© 2026 Daniil Khanin · khanin.info · HB-05
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74HC390 …
11
74HC08
1×
1
10×
74HC08
1A
1Q1
1B
1Q2
2A
2Q1
2B
2Q2
3A
GND
3B
GND
4A
GND
4B
GND
1Y
1d3
2Y
2d3
3Y
4Y
12
74HC86
1×
10×
74HC86
1A
1Q1
1B
1Q2
2A
2Q1
2B
2Q2
3A
GND
3B
GND
4A
GND
4B
GND
1Y
1d2
2Y
2d2
3Y
4Y
13
74HC74
1×
2
12×
74HC74
1RD
1nMR
1D
1Q0N
1CP
1c0
1SD
VCC
2SD
VCC
2CP
1c1
2D
1d1
2RD
1nMR
1Q
1Q0
1QN
1Q0N
2QN
1Q1N
2Q
1Q1
© 2026 Daniil Khanin · khanin.info · HB-05
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74HC390 …
14
74HC74
1×
2
12×
74HC74
1RD
1nMR
1D
1d2
1CP
1c1
1SD
VCC
2SD
VCC
2CP
1c1
2D
1d3
2RD
1nMR
1Q
1Q2
1QN
1Q2N
2QN
1Q3N
2Q
1Q3
15
74HC74
1×
2
12×
74HC74
1RD
2nMR
1D
2Q0N
1CP
2c0
1SD
VCC
2SD
VCC
2CP
2c1
2D
2d1
2RD
2nMR
1Q
2Q0
1QN
2Q0N
2QN
2Q1N
2Q
2Q1
16
74HC74
1×
2
12×
74HC74
1RD
2nMR
1D
2d2
1CP
2c1
1SD
VCC
2SD
VCC
2CP
2c1
2D
2d3
2RD
2nMR
1Q
2Q2
1QN
2Q2N
2QN
2Q3N
2Q
2Q3
17
Ctrl
+
G
Library
…
Chip N
2×
Library
…
74HC390
Enter
74HC390
1CP0
1MR
1CP1
2CP1
2MR
2CP0
1Q0
1Q1
1Q2
1Q3
2Q3
2Q2
2Q1
2Q0
© 2026 Daniil Khanin · khanin.info · HB-05
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CANVAS
18
1
1Hz
2Hz
10Hz
60Hz
4kHz
…
MAX
19
Hz
1×
0
1×
Q
Q
1×
3×
1Hz
CLK
0
RUN
Reset
Reset
RST
20
74HC08
1×
1
9×
74HC08
1A
CLK
1B
RUN
2A
GND
2B
GND
3A
GND
3B
GND
4A
GND
4B
GND
1Y
TICK
2Y
3Y
4Y
21
74HC390
1×
14×
74HC390
1CP0
TICK
1MR
RST
1CP1
U0
2CP1
T0
2MR
RST
2CP0
U3
1Q0
U0
1Q1
U1
1Q2
U2
1Q3
U3
2Q3
T3
2Q2
T2
2Q1
T1
2Q0
T0
© 2026 Daniil Khanin · khanin.info · HB-05
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CANVAS …
22
4b
0
A
2×
1×
1×
4b
0
T
4b
0
U
TICK
1
RUN
RUN = 1: 00 → 99
© 2026 Daniil Khanin · khanin.info · HB-05
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← Back to the lesson
Lesson 3. A counter in a package: 74HC390 and a stopwatch