The Arduino Motor Shield must be powered by an external power
supply because the L298 IC mounted on the shield has two separate power
units, one for the logic and one for the motor supply driver. The
current draw for the motor supply is often than the USB can give.
External (non-USB) power can come either from
an AC-to-DC adapter (wall-wart) or battery. The adapter can be connected
by plugging a 2.1mm center-positive plug into the Arduino's board power
jack on which the motor shield is mounted or by connecting the wires
that lead the power supply to the Vin and GND screw terminals, taking
care to respect the polarities.
To avoid possible damage to the Arduino board
on which the shield is mounted, we reccomend using an external power
supply that provides a voltage between 7 and 12V. If your motor require
more than 9V we recommend that you separate the power lines of the
shield and the Arduino board on which the shield is mounted. This is
possible by cutting the "Vin Connect" jumper placed on the back side of the shield. The absolute limit for the Vin at the screw terminals is 18V.
The power pins are as follows:
The shield can supply 2 amperes per channel, for a total of 4 amperes maximum.
This shield have two separate channels, called A and B, that each use
4 of the Arduino pins to drive or sense the motor. In total there are 8
pins in use on this shield.
You can use each channel separately to drive two DC motors or combine
them to drive one unipolar stepper motor.
The shield's pins, divided by channel are shown in the table below:
If you don't need the Brake and in the Current
Sensing and you also need more pins for your application you can disable
this features by cutting the respective jumpers on the back side of the
The additional sockets on the shield are described as follow:
Brushed DC motor. You can drive two Brushed DC
motors by connecting the two wires of each one in the (+) and (-) screw
terminals for each channel A and B. In this way you can control its
direction by setting HIGH or LOW the DIR A and DIR B pins, you can control the speed by varying the PWM A and PWM B duty cycle values. There are also the Brake A and Brake B
pins that if setted in HIGH state they brakes the DC motor faster than
when you power off the motor. You can know the current going through the
DC motor by reading the SNS0 and SNS1
pins. On each channel will be a voltage proportional to the measured
current, which can be read as a normal analog input, through the
functions analogRead() on the analog input A0 and A1. For your
convenience it is calibrated to be 3.3V when the channel is delivering
its maximum possible current, that is 2A.
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