Silicon Chip – April 2019

24 Silicon chip Australia’s electronics magazine siliconchip.com.au

MR

Vss

Vdd

LCK DS

Q0Q1Q2Q3Q4Q5Q6Q7Q7'

OE

1 2 3 4 5 6 7

8

9

12 11 14 13 10

15

16

SRCK

IC1

7H 4 C5 95

IC1

7H 4 C5 95

MR

Vss

Vdd

LCK DS

Q0Q1Q2Q3Q4Q5Q6Q7Q7'

OE

1 2 3 4 5 6 7

8

9

12 11 14 13 10

15

16

SRCK

IC2

7H 4 C595

IC2

7H 4 C595

1 2

3 4

1 2

3 4

1 2

3 4

1 2

1 3 4

2 3

4 5

7 6

16 8

15 14

1213

10 11

9

VCC1 VCC2

1,2EN

3,4EN

1A

2A

3A

4A

1Y

2Y

3Y

4Y

1

2 3

4 5

7 6

16 8

15 14

1213

10 11

9

VCC1 VCC2

1,2EN

3,4EN

1A

2A

3A

4A

1Y

2Y

3Y

4Y

1

2 3

4 5

7 6

16 8

15 14

1213

10 11

9

VCC1 VCC2

1,2EN

3,4EN

1A

2A

3A

4A

1Y

2Y

3Y

4Y

1

2 3

4 5

7 6

16 8

15 14

1213

10 11

9

VCC1 VCC2

1,2EN

3,4EN

1A

2A

3A

4A

1Y

2Y

3Y

4Y

CON3

1000 mF

+12V +12V

GND GND

+12V +12V +12V +12V

+3.3/5V +3.3/5V +3.3/5V +3.3/5V

IC3 L293DIC3 L293D

CON5

IC4 L293DIC4 L293D

CON6

+3.3/5V +3.3/5V

GND GND GND GND

DIN

DOUT DIN

DOUT

LT LT LT LT

CK CK CK CK

EN EN EN EN

33 mF 1kW

+3.3/5V

CON1 CON2

CON4

CON7

IC5 L293DIC5 L293D

CON8

IC6 L293DIC6 L293D

ÓSC (^20 1 9) FLIPDOT DISPLAY DRIVER
P1 P2 P3
P4 P5
P7 P6
P8 P9
P10
P11
P12
P13 P14 P15
COM
TO CONNECT
WITH FURTHER
DRIVERS
TO 12V
POWER
SUPPLY
TO CONNECT
WITH MCU OR
PREVIOUS
DRIVER
between the ‘on’ and ‘off’ states.
Due to the limited strength of the
electromagnets, the display will only
work reliably when standing upright,
which it will comfortably do without
any extra parts.
Driving the display
The display driver circuit is shown
in Fig.1. It is designed to be controlled
by a microcontroller using a simple se-
rial bus, and is powered from a 12V DC
supply. It connects to the coil circuit,
shown in Fig.2, via headers CON5-
CON8. This circuit represents one set
of 3 x 5 pixels that can display a sin-
gle character; characters can be daisy
chained to form larger displays. We’ll
explain how that works shortly.
The driving signals from the micro-
controller are fed in via six-pin header
CON1. They pass to IC1 and IC2, two
74HC595 shift registers, which decode
the serial data stream and use it to con-
trol the state of sixteen separate digi-
tal outputs (QA-QH on each IC). These
control signals will normally be either
0V (low) or 3.3-5V (high).
These digital outputs connect to the
control inputs of IC3-IC6, four L293D
dual H-bridge motor drivers, which
provide the current required to drive
the fifteen coils, as well as convert-
ing the 0-3.3/5V control signal volt-
age swing into a higher 0-12V swing
to drive the coils.
Fifteen of the motor driver outputs
connect to one end of each coil, with
the sixteenth output driving the other
The mechanism of a commercial flip-
dot display. The discs are around
9mm across and are driven by
coils of enamelled wire.
The magnetism
remaining after
the current has
ceased is enough to
hold the discs in their
last position, or even
snap them back if
they are moved.