DC Motor Control

Posted on Feb 6, 2014

We used buffer IC`s (7417, 7414) to isolate the signals to and from the Arduino. This protected the board, and provided power for external devices without drawing it from the Arduino. An H-bridge can be thought of in much the same way. It is the interface between an electrical signal and an electrical power source. Though they share thesame medium, their functions are vastly different.

DC Motor Control
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The H-bridge is a common circuit used to control the speed and direction of a DC motor with low current PWM signals. The H-bridge you will be using is the TA7291P ( datasheet ). It is a pair of half bridges that can source 1 Amp. DC motors are turned on by applying a voltage across the two terminals. The rotation speed can be controlled by increasing or decreasing the applied voltage. Changing the polarity of the applied voltage changes the motor`s direction of rotation. We can use half bridges to control both the speed and direction of rotation of a DC motor. Half bridges are essentially high power digital buffers; the output goes to 0V when the input is low, and the output goes to Vs when the input is high. To power a motor, we can use half bridges to drive one terminal high and the other low. We also can control the voltage applied to the motor by sending one half bridge a PWM signal. For example, if we hold one bridge low and drive the other bridge high 50% of the time, (for Vs=+12) the motor will behave as if we applied 6VDC. Notice that we can apply zero volts to the motor by either driving both bridges low or both high. Some h-bridges are designed so that one of these modes puts the outputs in a "coast to stop" mode (L-L for the TA7291P); the other mode causes a stronger "brake" stop. In this lab, you will be using only the digital output buffer and the voltage follower. As breadboard space is limited, these are the...

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