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Introduction
History: how light learned to count people
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. The beam and CD4011
1.1. Idea: how a shop counts people
1.2. Idea: the CMOS 4000 series
1.3. Idea: NAND for everything
1.4. Build
1.5. Check
Lesson 1 paste (Cmd+I)
Lesson 2. The F/F flip-flop
2.1. Idea: a counter is flip-flops that flip
2.2. Idea: flipping through exclusive OR
2.3. Idea: a NAND with three inputs
2.4. Build
2.5. Check
Lesson 2 paste (Cmd+I)
Lesson 3. The CD4029B counter
3.1. Idea: which bit to flip
3.2. Idea: controlling the counter
3.3. Idea: the bubbles on the TI drawing
3.4. Build
3.5. Check
Lesson 3 paste (Cmd+I)
Lesson 4. The CD4511B decoder
4.1. Idea: seven strokes
4.2. Idea: latch, blanking, lamp test
4.3. Idea: a switch on two transistors
4.4. Build
4.5. Check
Lesson 4 paste (Cmd+I)
Lesson 5. Direction
5.1. Idea: two beams one after another
5.2. Idea: remember the first
5.3. Idea: the clock is when both are blocked
5.4. Build
5.5. Check
Lesson 5 paste (Cmd+I)
Lesson 6. The visitor counter
6.1. Idea: two displays on the same beams
6.2. Idea: two digits — two counters
6.3. Idea: Reset holds
6.4. Build
6.5. Check
Lesson 6 paste (Cmd+I)
Summary
All the parts
Instructions in pictures
Lesson 5 in pictures
← Back to the lesson: Lesson 5. Direction
5
Direction
two beams: which one is blocked first
kh
HT-04
A
B
A
B
A
B
VCC
1×
GND
1×
E
2×
R
2×
CD4011
2×
1
5×
∞
© 2026 Daniil Khanin · khanin.info · HT-04
50
CANVAS
1
Delete
0
UD
1Hz
CLOCK
Reset
Reset
RST
2
Delete
CD4029
PE
RST
J4
GND
J1
GND
CI
GND
BD
GND
UD
UD
J2
GND
J3
GND
CLOCK
CLOCK
Q4
U3
Q1
U0
CO
Q2
U1
Q3
U2
CD4511
B
U1
C
U2
LT
VCC
BL
VCC
LE
GND
D
U3
A
U0
e
Ue
d
Ud
c
Uc
b
Ub
a
Ua
g
Ug
f
Uf
© 2026 Daniil Khanin · khanin.info · HT-04
51
CANVAS …
3
pairs one under the other: beam A on top (street), beam B below (shop floor)
4
VCC
1×
GND
1×
2×
VCC
VCC
GND
GND
5
E
2×
R
1×
3×
VCC
E1
R1
BA
VCC
E2
6
R
1×
1×
R2
BB
7
CD4011
1×
1
12×
CD4011
A
BA
B
BA
C
BB
D
BB
E
XA
F
BB
G
XB
H
BA
J
XA
K
XB
L
SIN
M
SOUT
© 2026 Daniil Khanin · khanin.info · HT-04
52
CANVAS …
8
CD4011
1×
1
12×
CD4011
A
SIN
B
OUT
C
SOUT
D
IN
E
XA
F
XB
G
NBOTH
H
NBOTH
J
IN
K
OUT
L
NBOTH
M
BOTH
9
5×
5×
XA
XB
IN
OUT
BOTH
10
Alt/⌘ + click on a beam — blocked and fixed; again — cleared
A
B
A
B
A
B
A, both, B — IN, BOTH, OUT
IN
BOTH
OUT
© 2026 Daniil Khanin · khanin.info · HT-04
53
← Back to the lesson
Lesson 5. Direction