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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 4 in pictures
← Back to the lesson: Lesson 4. A decoder in a package: 74HC138 and a running light
4
Decoder: 74HC138
a running light on 16 lamps
kh
HB-05
74HC138
L0
L1
L2
L3
L4
L5
L6
L7
IN
6×
OUT
8×
74HC04
2×
1
74HC08
2×
1
74HC00
2×
1
Hz
1×
Q
Q
1×
74HC74
2×
2
16×
∞
Ctrl
+
G
74HC138
© 2026 Daniil Khanin · khanin.info · HB-05
38
CANVAS
1
Delete
1Hz
CLK
0
RUN
Reset
Reset
RST
4b
0
T
4b
0
U
TICK
2
Delete
74HC08
1A
CLK
1B
RUN
2A
GND
2B
GND
3A
GND
3B
GND
4A
GND
4B
GND
1Y
TICK
2Y
3Y
4Y
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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74HC138
3
IN
6×
OUT
8×
A0
A1
A2
E1
E2
E3
Y7
Y6
Y5
Y4
Y3
Y2
Y1
Y0
4
74HC04
1×
1
11×
74HC04
1A
A0
2A
A1
3A
A2
4A
E1
5A
E2
6A
GND
1Y
nA0
2Y
nA1
3Y
nA2
4Y
nE1
5Y
nE2
6Y
5
74HC08
1×
1
12×
74HC08
1A
nA1
1B
nA0
2A
nA1
2B
A0
3A
A1
3B
nA0
4A
A1
4B
A0
1Y
t0
2Y
t1
3Y
t2
4Y
t3
© 2026 Daniil Khanin · khanin.info · HB-05
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74HC138 …
6
74HC08
1×
1
12×
74HC08
1A
nE1
1B
nE2
2A
g
2B
E3
3A
G
3B
nA2
4A
G
4B
A2
1Y
g
2Y
G
3Y
G0
4Y
G1
7
74HC00
1×
1
12×
74HC00
1A
G0
1B
t0
2A
G0
2B
t1
3A
G0
3B
t2
4A
G0
4B
t3
1Y
Y0
2Y
Y1
3Y
Y2
4Y
Y3
8
74HC00
1×
1
12×
74HC00
1A
G1
1B
t0
2A
G1
2B
t1
3A
G1
3B
t2
4A
G1
4B
t3
1Y
Y4
2Y
Y5
3Y
Y6
4Y
Y7
9
Ctrl
+
G
Library
…
Chip N
2×
Library
…
74HC138
Enter
74HC138
A0
A1
A2
E1
E2
E3
Y7
Y6
Y5
Y4
Y3
Y2
Y1
Y0
© 2026 Daniil Khanin · khanin.info · HB-05
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CANVAS
10
2
1Hz
2Hz
10Hz
60Hz
4kHz
…
MAX
11
Hz
1×
Q
Q
1×
2×
1Hz
CLK
Reset
Reset
CLR
12
74HC04
1×
1
7×
74HC04
1A
CLR
2A
GND
3A
GND
4A
GND
5A
GND
6A
GND
1Y
nCLR
2Y
3Y
4Y
5Y
6Y
13
74HC74
1×
2
12×
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
14
74HC74
1×
2
12×
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
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CANVAS …
15
74HC138
1×
14×
74HC138
A0
Q0
A1
Q1
A2
Q2
E1
Q3
E2
GND
E3
VCC
Y7
L7
Y6
L6
Y5
L5
Y4
L4
Y3
L3
Y2
L2
Y1
L1
Y0
L0
16
74HC138
1×
14×
74HC138
A0
Q0
A1
Q1
A2
Q2
E1
GND
E2
GND
E3
Q3
Y7
L15
Y6
L14
Y5
L13
Y4
L12
Y3
L11
Y2
L10
Y1
L9
Y0
L8
17
5×
5×
L0
L1
L2
L3
L4
18
5×
5×
L5
L6
L7
L8
L9
© 2026 Daniil Khanin · khanin.info · HB-05
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CANVAS …
19
5×
5×
L10
L11
L12
L13
L14
20
1×
1×
L15
L0
L1
L2
L3
L4
L5
L6
L7
a "shadow" runs: one lamp goes out
© 2026 Daniil Khanin · khanin.info · HB-05
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← Back to the lesson
Lesson 4. A decoder in a package: 74HC138 and a running light