H-Bridge
Specifications
Phase 2 of Beginner Bot calls
for a Seeed Studio L298 dual
H-bridge motor control module,
available online from
RobotShop.com and other
retailers. This module provides the
L298 integrated circuit on a
heatsink, plus the required
protection diodes, operating LEDs,
and terminal blocks for wiring to a
power source and motors.
You can use most any other
L298 module, or even another
module using a different type of
H-bridge, as long as it conforms to
these basic specifications:
• Capable of driving up to two
amps per motor.
FIGURE 2. Concept of the electronic H-bridge. The direction of current flow
determines which way the motor turns.
You can make your own
H-bridge using an L298 chip. Be
sure to check the datasheet for the
device, and add the required
protection diodes on each of the
motor terminal outputs.
circuitry. This circuitry effectively
duplicates the action of those DPDT
switches. And because the circuitry
can be operated electrically, other
electronic components can be
connected as sensors to provide
automatic function.
An H-bridge circuit is the most
common way to provide all
electronic control of a motor. It’s
called an H-bridge because the
schematic diagram of the circuit
typically shows the main
components — usually transistors of
one type or another — in an “H”
pattern. Figure 2 shows a simplified
H-bridge (don’t try to build this circuit; it’s just for
demonstration).
While there are many — and I mean many — workable
H-bridge designs, most of the ones you can easily replicate
leave something to be desired. Most rely on big and bulky
transistors, so the finished circuit is ungainly. To make the
thing easier to construct at home, some components might
be omitted which could affect its efficiency.
It’s often easier (and sometimes cheaper!) to get a
ready-made H-bridge. A popular one is the L298 — a
complete H-bridge in a single integrated circuit. One L298
will operate two motors. The L298 comes in a special kind
FIGURE 3. Ready-made H-bridge module. This one is from Seeed Studio,
of high wattage package that isn’t designed for
breadboarding, and it needs some external parts —
specifically, a set of protection diodes — to complete its
circuitry.
SERVO 09.2011 37
