Design Meeting One – Building a Circuit to Control the Motors
(11/25/2009)
Our first rover schematic
Step 3 – Design Meeting One
During our first meeting we wanted to rough out a plan for the circuitry. The first design goal is basic locomotion and control of the 12-volt motors. Without even checking our notes, Larry and I both initially wanted to use an H-bridge.
Why did we both immediately jump to an H-bridge and what does that even mean?
The Mighty H-Bridge
The H-bridge is a simple circuit that uses 4 switches to change the polarity of a signal from positive to negative. When you lay the circuit out, it looks like the letter ‘H’ which is proof again that while engineers are good at building things, we aren’t good at creative names.
You can build your own H-bridge motor controller with a few parts.
Parts for an H-Bridge
We connect the switches in a square array with the motor in the center of the letter ‘H’ like this:
An H-Bridge waiting for a power source
When we connect the power source we can use the switches to determine which direction the current flows through the motor. With four switches we can create a truth table showing our possible states that are dependent on whether a switch is on or off.
The H-Bridge with the Truth Table
We can show how the motor will operate with the circuit like this:
The States of the H-Bridge and the Motor
With the H-bridge in place, we can spin the motor in either direction by toggling a few digital I/O pins. If you read Larry’s blog post concerning the H-Bridge you can see we selected a TA7291S H-Bridge made as a single chip by Toshiba.
The H-Bridge is a real gem of a circuit and is good choice for controlling any electric motor.
Trackbacks & Pingbacks