Pololu SMC01A User manual

Dual Serial
Motor Controller
User’s Guide
Contents:
Safety Warning
Parts List
Contacting Pololu
How to Solder
Assembly Instructions
Connecting the Motor Controller
Using the Motor Controller
How the Motor Controller Works
Description and Specifications
SMC01A
© 2001
http://www.pololu.com/
Pololu

Pololu 2
Important Safety Warning
This kit is not intended for young children! Assembly of this kit
requires high-temperature soldering and the use of sharp cutting
tools. Some included components may become hot, leak, or explode
if used improperly. Pololu strongly recommends that you wear
safety glasses when building or working with any electronic
equipment. Children should use this kit only under adult supervision.
By using this product, you agree not to hold Pololu liable for any
injury or damage related to the use or to the performance of this
product. This product is not designed for, and should not be used
in, applications where the malfunction of the product could cause
injury or damage.
!
Parts List
The following components are the motor controller parts. Make sure to verify that all
components are included, and that you know which component is which. Each
component is labeled with its reference number and description. There are 11 parts in
the kit, including the PCB.
C1
Electrolytic
Capacitor
(2 options)
C2
Tantalum
Capacitor
CONNECTOR
8-pin female
header
(2 options)
PCB
Printed Circuit
Board
U1
PIC12C508A
Microcontroller
and Socket
U2
SN754410
Dual H-Bridge
and Socket
U3
LM2931
5-volt Regulator
© 2001
http://www.pololu.com/

3
Pololu
soldering iron
solder
PCB
good bad
1: solder
2: check
3: trim leads
How to Solder
You need a soldering iron and diagonal cutters to assemble the motor controller. The
green printed circuit board (PCB) is the base that holds the components together and
establishes the necessary electrical connections. The PCB has two sides: a top side, or
component side, which has white
silkscreen markings, and a bottom side,
or solder side. Insert the components
from the top side and solder them on the
solder side. In general, you should
insert and solder the components so that
they are as close as possible to the PCB.
All components in this kit, except for
voltage regulator U3, should be flush
with the PCB. After soldering, trim
excess leads with diagonal cutters.
To solder, heat a component lead and the
PCB pad and then apply solder until the
solder flows onto both the lead and the
pad. If the solder beads up on the lead or
on the pad, the connection is bad, so you
should apply more heat. However, be
careful not to damage any components
through overheating.
Contacting Pololu
You can check the Pololu web site at http://www.pololu.com/ for latest
information about the motor controller, including color pictures, application examples,
and troubleshooting tips.
We would be delighted to hear from you about your project and about your experience
with our motor controller. You can contact us through our online feedback form or by
email at [email protected]. Tell us what we did well, what we could improve,
what you would like to see in the future, or anything else you would like to say!
top
bottom
© 2001
http://www.pololu.com/

SMC01A
C2
C1
U3
U2
U1
M2
12M1
4
Pololu
Insert the 8-pin socket from the top side of the PCB in
the area indicated U1, and solder. On one side of the
socket is a notch that should be aligned with the notch
on the PCB drawing. The socket protects the PIC
microcontroller from being damaged during soldering.
Assembly Instructions
Caution: The components U1-U3 can be damaged by static electricity. Ground
yourself (touch a water pipe or the metal frame of a piece of electrical equipment)
before handling these components, and avoid touching their leads. Once assembled,
the motor controller can be stored safely in the conductive bag in which the kit is
packaged.
1
SMC01A
C2
C1
U3
U2
U1
M2
12M1
Solder the 16-pin socket in the area indicated U2.
Make sure to align the notch on the socket with the
notch on the PCB drawing. The socket allows you to
replace the motor driver chip if it ever breaks.
2
Assembly Options
You can assemble the motor controller in several ways, so before you begin, there are
three choices you must make. The options concern the size of the assembled motor
controller. You can insert the various components into the PCB without soldering to
help determine which options are best for you.
Should I use IC sockets for U1 and U2? The sockets are not necessary, and not using
them will make your motor controller slightly smaller. Not using them, however, will
make it much more difficult to replace the ICs if they are damaged, and also make it
possible for you to damage the devices while soldering. We strongly recommend
using the sockets.
Which C1 option should I use? Two electrolytic capacitors are provided in the kit.
The larger capacitor is rated for 25 volts, whereas the smaller one is rated for 16 volts.
These ratings limit the voltage you can apply to the motor controller and thus limit the
maximum voltage with which you can drive the motors. If you want to drive the
motor with voltages higher than 16 volts, or if you don’t care about size, use the
larger capacitor.
Which connector should I use? A straight connector and a right-angle connector are
provided in the kit. It is up to you which you choose to use; you can also solder motor
leads directly into the PCB holes and avoid using a connector altogether.
© 2001
http://www.pololu.com/

Next, solder in your choice of connector. You can use
either the straight or the right-angle female header
provided in your kit, or use your own connector. If you
prefer having leads soldered directly to the PCB, you
can do so now or wait until you have the leads ready and
available.
6
SMC01A
C2
C1
U3
U2
U1
M2
12M1
Finally, insert the two integrated circuits (ICs), U1
and U2, into their sockets. Make sure that you plug
them in so that the notches on the ICs match the
notches on the PCB outline. Do not solder the ICs
to the sockets. If you soldered the sockets in
backwards, it doesn’t matter as long as the actual
component is oriented correctly. Be careful: the ICs
are static-sensitive, so take appropriate precautions
and avoid touching their leads. You may need to bend
some of the leads to make them fit in the sockets; if so,
hold the plastic body of the IC and push the pins
(gently!) against a flat surface, one row at a time.
7
SMC01A
C2
C1
U3
U2
U1
M2
12M1
5
Pololu
SMC01A
C2
C1
U3
U2
U1
M2
12M1
Next, add the tantalum capacitor C2. You may need to
bend the leads to make them straight so that they will
fit. The capacitor is polarized, which means it must
only go in one way. Make sure the side labeled with a
“+” and a stripe goes into the hole that is also marked
with a “+”. If the PCB is oriented as shown in the
diagram, the lower hole is for the positive lead.
3
+
SMC01A
C2
C1
U3
U2
U1
M2
12M1
Now, add the voltage regulator, U3. Make sure the
device is oriented as shown on the silkscreen drawing,
with the flat side facing the outside of the PCB.
Caution! The voltage regulator can be damaged by
static electricity.
4
SMC01A
C2
C1
U3
U2
U1
M2
12M1
In this step, add your choice of electrolytic capacitor for
C1. The larger capacitor is necessary if you want to run
your motors off of a 24-volt power source, and you
should use it if you don’t care about the size of the
completed motor controller. The electrolytic
capacitors are polarized, but this time the stripe
identifies the negative terminal. Also, the positive
lead is longer. Make sure to match up the positive lead
with the appropriate hole in the PCB.
5
+
+
© 2001
http://www.pololu.com/

6
Pololu
Connecting the Motor Controller
There are eight pins on the bottom of the motor
controller for connecting it to the rest of your system.
A closeup of the bottom of the PCB is shown to the
right, in case you have a hard time reading the
silkscreen on your board. The eight pin
labels and the corresponding functions are
shown in the table.
Connecting Power. Warning:
connecting power incorrectly can cause
some components to explode. Connect
the ground pin to a ground terminal on
your robot controller. If you have a
separate power supply for just the motors,
make sure that you connect the negative
terminal of that supply to the same ground.
(This situation may arise if, for example, you want to run your robot controller off of a
9-volt battery and you want to run your motors off of a 12-volt battery. You will also
need an independent power supply for the motors if you want to use a personal
computer as the robot controller. In that case, you might use a battery for the motor
supply and use a wall outlet for the PC supply.) Connect the ‘+’ pin to the positive
terminal of the motor supply; this terminal may connect only to the motor controller, or
it may connect to any other device powered by that supply. Warning: the supply
voltage may not exceed 16 volts or 25 volts, depending on which capacitor you chose
for C1 in step 5 of assembly.
Reset Input. The reset input is optional, but you
C
may need to use it to ensure that
spurious signals sent when your robot controller turns on do not cause the motor
controller to detect the baud rate incorrectly. onnect this pin to a 0-5V digital output
on your robot controller. The line should normally be kept high (+5V), but bringing it
low (to 0V) for at least 2 microseconds resets the motor controller to its initial state (all
motors off, waiting for its first serial command).
Serial Input. Use a pin on your robot controller that can be used as a TTL-level,
asynchronous serial output. Serial data can be sent down this line 8 bits at a time, with
no parity bit, at any rate between 1200 and 19200 baud. Once you choose a baud rate,
you cannot change it until the motor controller is reset. Important note: unlike
RS-232 serial lines (the standard for serial ports used to connect devices to personal
computers), this line uses TTL voltages (between 0 and 5 volts). The higher voltages
used on RS-232 lines will damage the motor controller. If you need to convert RS-232
levels to TTL levels, you will need to use a level converter such as the MAX220 (made
by Maxim). You could also use the simple circuit shown at the top of the next page.
When building circuits that connect to a PC, be especially careful because you
could potentially destroy the PC’s serial port. Before attempting to connect your
own electronics to a computer, make sure you know what you are doing!
LABEL FUNCTION
-
+
1
2
M1+
M2-
M2-
M1-
ground (0V)
positive supply (5.6-25V)
reset
serial control input
motor 1, negative output
motor 2, positive output
motor 1, positive output
motor 2, negative output
© 2001
http://www.pololu.com/

7
Pololu
U3
SMC01A
C1
M2M2
1122M1M1
MOTOR
BATTERY
GND OUT1 OUT2
ROBOT
CONTROLLER
OUT1: RESET
OUT2: CONTROL
Connecting the Motors. Connect one or two motors to the pins labeled M1 and M2.
You probably don’t need to worry too much about the polarity, but the ‘+’ pins go
positive when the controller receives a “forward” command. If you find out that your
motors turn in different directions than you expect, you can flip the wiring or just
switch the forward and reverse commands on your robot controller program.
to 5V
(off C2+)
to serial
control
input (’2’)
to ground (’-’)
3
2
1
9
6
2
7
8
4
5
DB9 serial
port connector
R2
10k
R1
4.7k
Q1
2N2222
Bold
circles
indicate pads
that are connected
to 5V, which you can use
with the circuit shown on the left
SMC01A
C2
C1
U3
The above diagram shows a simple circuit for connecting the motor controller to a PC
serial port. You will need to connect one side of resistor R1 to a 5V supply, which is
available on the PCB at the points indicated on the figure to the right. You can solder a
wire onto one of the pads, but make sure that the wire touches only the intended pad.
A typical setup is shown in the diagram below. Keep in mind that the wiring
you use for the motor outputs and power connections should be capable of
conducting several amps. We recommend using at least 26 gauge wire
(remember, smaller numbers mean bigger wires!).
© 2001
http://www.pololu.com/

start byte = 0x80 device type = 0x00 motor # and direction motor speed
Using the Motor Controller
To set the speed and direction of a motor, send a four-byte command with the following
structure to the motor controller’s asynchronous serial input, labeled ‘2’ on the PCB.
You must send the four-byte command eight bits at a time (with no parity bit) at a
constant baud rate ranging from 1200 to 19200 baud. The serial bits must be non-
inverted, meaning that a zero is sent as a low
voltage, and a one is sent as a high voltage, as shown
in the diagram to the right. (The PC-connection
circuit on the previous page corrects the inverted
signal coming out of PC serial ports.) Commands
sent to the serial input must conform to the above
format (described in detail below) or else the motor
controller and other devices connected to the serial
line may behave unexpectedly. This motor controller interface protocol is compatible
with other Pololu serial devices such as our servo controller, so you can control
multiple Pololu serial devices on a single line.
The Four-byte Motor Controller Command
Byte 1: Start Byte. This byte should always be 0x80 (128 in decimal) to signify the
beginning of a command. The start byte is the only byte with the highest bit (bit 7) set,
and it alerts all devices on the serial line that a new command is being issued. All
succeeding bytes sent down the serial line must have their highest bit cleared to zero.
Byte 2: Device Type. This byte identifies the device type for which the command is
intended, and it should be 0x00 for commands sent to motor controllers. All devices
that are not SMC01A dual motor controllers ignore all subsequent bytes until another
start byte is sent.
Byte 3: Motor Number and Direction. This byte
has three parts, as shown in the diagram to the right:
"Bit 0 specifies the direction of the motor. Set
this bit to 1 to make the motor go forward; clear
the bit to make it go backward.
"Bits 1-6 specify the motor number. If you are
using only two motors per serial line, you can
use the default values of 0 for motor M1 and 1 for
motor M2. If you want to control more than two
motors, use numbers in the range of 2 to 63, as
described in the section, “Controlling Multiple Motor Controllers with One Serial
Line”.
bit 0: direction
1 = forward
0 = reverse
bit 7 bit 0
0x x x x x x x
bits 1-6: motor
number
bit 7: always 0
8
Pololu
10011010
start bit stop bit
5V
0V
LSB MSB
© 2001
http://www.pololu.com/

Byte 3: Motor Number and Direction (continued).
"Bit 7 must be cleared since this is not a start byte.
To obtain the complete byte 3 value from a motor number and a direction, multiply the
motor number by 2 and add 1 if the direction is forward. For example, to make motor 5
go forward, byte three should be 5 x2 + 1 = 11. To make motor 1 go backward, byte 3
should be 1 x2 = 2. (Two efficient ways to multiply by 2 in a microcontroller program
are shifting left by one digit or adding the motor number to itself.)
Byte 4: Motor Speed. The most significant bit must be zero since this is not a start
byte, and the remaining seven bits are available for specifying the speed. The possible
range of values for byte 4 is thus 0x00 to 0x7F (0 to 127 decimal). 0x00 turns the motor
off, and 0x7F turns the motor fully on; intermediate values correspond to intermediate
speeds.
Resetting the Motor Controller
The motor controller’s optional reset line should normally be kept high at +5V. Pull the
reset line low to 0V for at least 2 microseconds to reset the motor controller to its initial
state (all motors off, waiting for the first serial command). You do not need to reset the
motor controller to use it successfully. However, you may need to reset the motor
controller to ensure that spurious signals sent when your robot controller turns on do
not cause the motor controller to detect the baud rate incorrectly.
Controlling Multiple Motor Controllers with One Serial Line
To control a particular motor, you must specify its motor number in command byte 3.
For all motor controller boards, motor M1 responds to commands for motor number 0,
and M2 responds to commands for motor number 1. To control more than two motors
with a single serial line, you need to use motor numbers 2 through 63. Motor
controllers that are not specially ordered respond to numbers 2 and 3; you need to order
specially programmed motor controllers to use motor numbers 4 through 63.
For example, to control six motors independently, you need three motor controller
boards, each with different motor numbers. All three motor controllers respond to
commands for motor numbers 0 and 1. For controlling the six motors independently,
use motor numbers 2, 3, 4, 5, 6, and 7. (The exact numbers depend on which motor
numbers you request when you specially order additional motor controllers.)
You can individually control up to 62 motors at a time with a single serial line using 31
motor controllers: one with the default program and 30 that are specially programmed.
9
Pololu
© 2001
http://www.pololu.com/

Example BASIC Stamp II Program
This program, which can run on a BASIC Stamp II controller, makes motor 1 gradually
speed up, then slow down, then speed up in the other direction, and then slow down
again. For the code to work, pin 15 must be connected to the reset input (‘1’), and pin
14 must be connected to the serial input (‘2’). The interface code should look similar in
other programming languages; the description below should help you in understanding
the code and, if necessary, in translating it to other languages.
On line 1, the 8-bit variable speed is declared for later use. The motor controller is
then reset by a low-going pulse on pin 15 (lines 2 and 3).
The first for loop on lines 4-7 causes motor 1 to gradually speed up. The serial output is
created by the serout statement on line 5. The first parameter, 14, specifies the pin
number through which to send the serial signal. The next parameter, 32, sets up the
serial characteristics to be 8 bits with no parity, non-inverted, at a baud rate of 19200.
The four numbers in square brackets are the data to be sent, and they correspond to the
four control bytes for the motor controller. The first two bytes should always be $80
and 0. The second 0makes motor 1 go backward. The speed variable, which increases
every time through the loop, is the only part of the command that changes, and that is
what makes the motor gradually speed up. The pause statement on line 6 causes the
program to wait for 20 ms (0.02 seconds) before sending the next command.
When the first loop ends, the motor is set to its full speed of 127. The second loop on
lines 8-11 slows the motor back down by sending speeds from 127 down to 0. The next
two loops on lines12-19 then repeat the process, except for the parameter value of 1in
byte three, which causes motor 1 to spin forward.
1speed var byte
2low 15 'reset motor controller
3high 15
4for speed = 0 to 127
5serout 14,32,[$80, 0, 0,speed]
6pause 20
7next
8for speed = 127 to 0
9serout 14,32,[$80, 0, 0,speed]
10 pause 20
11 next
12 for speed = 0 to 127
13 serout 14,32,[$80, 0, 1,speed]
14 pause 20
15 next
16 for speed = 127 to 0
17 serout 14,32,[$80, 0, 1,speed]
18 pause 20
19 next
10
Pololu
© 2001
http://www.pololu.com/

How the Motor Controller Works
The motor controller uses H-bridges to turn motors forward and backward (see the
dotted ‘H’ in the left figure). H-bridges have four switches, which are turned on in pairs
to allow current to flow into the motors in both directions, as shown below. In the left
figure, all four switches are open, and the motor is turned off. When switches 1 and 4
close, the motor turns in one direction; when switches 2 and 3 close, the motor turns the
other way. Integrated circuit U2 contains two H-bridges, allowing bidirectional
control of two motors.
A technique called pulse width modulation (PWM) is used to control the speed of the
motors. The microcontroller (U1) is a little computer that controls the H-bridge
switches. It turns the switches on and off very rapidly (600 times per second) and
varies the percentage of the time that the switches are on to achieve the speed set by the
serial interface. For a higher speed, the switches are on a larger fraction of the time than
for a slower speed. At the maximum speed of 127, the switches are left on. The
momentum of the motor shaft keeps the shaft spinning at a constant speed that can be
varied smoothly over all 127 different speeds.
U3 and the capacitors provide a steady 5V power supply for the microcontroller, which
cannot run at the full motor voltage provided to the board at the ‘+’ and ‘-’ pins.
The complete schematic diagram of the motor controller is shown below:
11
Pololu
VIN VOUT
GND
LM2931
U3
SN754410
1,2EN
1Y
1A
GND
GND
2A
2Y
VMOT
VCC
3Y
4A
GND
GND
3A
4Y
3,4EN
4
5
12
13
2
7
10
15
1
8
9
16
3
6
11
14
U2
PIC12C508A
GP2
VSS
VCC
GP0
GP1
GP4
MCLR GP5
4
3
8
15
7
2
6
U1
C1
100
C2
22
+
2
-
1
+
-
+
-
M1
M2
M
V+
V-
M
V+
V-
M
V+
V-
12
43
12
43
12
43
© 2001
http://www.pololu.com/

The Pololu Dual Serial Motor Controller
For a robot to interact with its environment, it must be able to convert
electrical signals into motion. However, the power requirements of
actuators, electrical devices capable of producing motion, are typically
so high that normal digital circuitry cannot drive them. In addition,
precise motion control requires constantly changing the signals sent to
the actuators, leaving the control circuitry with little time to attend to
other tasks.
The Pololu motor controller bridges the gap between robot controllers
and power-hungry actuators. Using one serial output from your robot
controller, you can independently set each of two small DC motors (the
kind typically found in remote-control cars and motorized toys) to go
forward or backward at any of 127 different speeds. To control
additional motors, you can connect multiple motor controllers to the
same serial line. The motor controller is compatible with the Pololu
Servo Controller, so you can control an almost unlimited number of
motors and servos with one serial line. Because of its small size, the
motor controller can fit almost any robot design.
Specifications
PCB size................................. 1.00" x0.85"
Motor ports............................. 2
Speeds.................................... 127 forward, 127 backward, and off
Maximum current................... 1 A per motor (continuous)
Supply voltage........................ 5.6-25 V
Data voltage............................ 0 and 5 V
PWM frequency...................... 600 Hz
Serial baud rate....................... 1200-19200 (automatically detected)
12
Pololu
© 2001
http://www.pololu.com/