N04
page 1 of 11
Rotary Encoders
Incremental optical encoders
Arduino +5V
D
+
1K
Arduino digital input
external GND
+
external +5V
E
5K
Arduino GND
uni-directional single track encoder
count pulses to measure distance
count pulses per time (or time per pulse) to measure speed
cannot ascertain direction of rotation
= photo pickup

=0
=1
Q
t
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bi-directional incremental encoders require quadrature and an up/down counter
quadrature - determine direction of rotation with two pickups
can use 4X extended counting
CCW
A
B
A leads B
A
A
D
B
B
Q
CLK
CCW / CW
positive edge
D flip-flop
(Q captures value of A
when positive edge
appears on B)
CW
B leads A
A
B
single track - two pickups offset by ¼, ¾, 1 ¼ … pitch
A
B
A
B
incremental encoders often have a home mark
must start counting from an internal or external home position to get absolute position
can be a problem if power goes down
N04
Incremental magnetic encoder using Hall effect sensor
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N04
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Absolute optical encoder
8 bit absolute encoder requires 8 pickups that are precisely aligned on radial line
Gray code pattern
Binary pattern
N04
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Stepping Motors
A
B
D
C
Wave Drive Sequence (full steps)
Step
A
B
C
D
1
ON
2
ON
3
ON
4
ON
5
ON
Two-Phase Drive Sequence (full steps)
Step
A
B
C
D
1
ON
ON
2
ON
ON
3
ON
ON
4
ON
ON
5
ON
ON
Half-Step Drive Sequence (half steps)
Step
A
B
C
D
1
ON
2
ON
ON
3
ON
4
ON
ON
5
ON
6
ON
ON
7
ON
8
ON
ON
9
ON
(Allegro Microsystems UCN5804 spec sheet)
N04
ULN2803A
1C 18
1 1B
Arduino
digital
outputs
Arduino
GND
2 2B
2C
3 3B
3C
17
4 4B
16
6
4C 15
5 5B
5C
14
6 6B
6C
13
7 7B
7C
12
8 8B
8C
11
COM
10
9 GND
motor coils
A
C
B
D
external
power
+5VDC
external
power
GND
6 wire stepper
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5 wire stepper
4 wire stepper
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page 7 of 11
Permanent Magnet Direct Current (PMDC) Motors
output speed nominally proportional to input DC voltage
if motored, can be used to generate voltage nominally proportional to driven speed
not all motors are neutrally timed
+
has both internal resistance AND inductance
actual
theory
VIN
VIN
M
BJT collector
driven load
Unidirectional motor driver
linear mode - speed proportional to VIN
switched mode - full off, full on
pulse width modulation (PWM)
VIN
speed nominally proportional to duty cycle
VS
VS
M
M
VIN
B
ON
time
OFF
20% duty cycle provides about 20% speed
ON
time
70% duty cycle provides about 70% speed
D
C
RIN
cannot provide reverse rotation
OFF
FET drain
driven load
E
G
S
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Push-pull bidirectional driver
+15V
usually used in linear mode
NPN
requires bipolar VIN
C
B
requires bipolar supply
need same hFE for NPN and PNP
crossover distortion
E
VIN
E
RIN
B
PNP
C
-15V
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page 9 of 11
H-bridge bidirectional motor driver
unipolar control and supply voltages
never A and C
never B and D
Battery +
Battery +
A
Battery +
B
DC
motor
C
Battery -
Battery +
A
D
B
DC
motor
C
Battery -
Battery -
H-bridge CW rotation
D
Battery -
H-bridge CCW rotation
H-bridges must drive high-side base/gate voltages A and B higher than VM  R M i M
can provide battery charging during regenerative braking
Battery +
Battery +
A
Battery +
B
Base A
Battery +
A
B
Base B
Gate A
DC
motor
C
D
Base C
Gate B
DC
motor
C
D
Base D
Gate C
Battery -
Battery -
NPN BJT H-bridge
Gate D
Battery -
Battery -
N-channel FET H-bridge
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page 10 of 11
totem-pole H-bridge uses NPN and PNP (or N-channel and P-channel)
VA
0V
0V
> VM
> VM
Battery +
VA
VB
0V
> VM
0V
> VM
i
0
0
→
0
Battery +
Battery +
VA
VB
NPN
NPN
DC
motor
NPN
DC
motor
VB
PNP
PNP
Battery -
Battery -
PNP
Battery -
totem-pole BJT H-bridge
SSR H-bridge precludes the need for base/gate high-side bias drivers
Battery +
Battery +
A
B
Input A
Input B
C
DC
motor
D
Input C
Input D
Battery -
Battery -
SSR (solid state relay) H-bridge
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page 11 of 11
L293D dual H-bridge
VCC1 (pin 16) is logic supply voltage = +5V
VCC2 (pin 8) is motor supply voltage = +4.5 V to +36 V
driver inputs (pins 2, 7, 10 and 15) are TTL compatible
ENABLE inputs (pins 1 and 9) are TTL compatible
driver outputs (pins 3, 6, 11 and 14) have same STATE (not same voltage) as inputs
drivers are capable of 1 A
fly-back diodes are included internally in L293D