Page 125 - PDA Robotics Using Your Personal Digital Assistant to Control Your Robot

PDA 05 5/30/03 11:35 AM Page 101
Chapter 5 / The Electronics
robot to retrieve and forward this information to the PDA (like the
range-finder information), where it can be displayed and analyzed. We
could determine the speed of PDA Robot based on the current draw
after calibrating on a hard, flat surface. This is not a very accurate
method of determining the speed and distance traveled, but it will
give you a good estimate. Things like the incline and traction will
affect the accuracy.

For higher currents, outputs can be paralleled. Take care to parallel
channel 1 with channel 4 and channel 2 with channel 3. Figure 5.46
shows how to accomplish this.

Power Output Stage. The L298 integrates two power output stages
(A; B). The power output stage is a bridge configuration, and its out-
puts can drive an inductive load in common or differential mode,
depending on the state of the inputs. The current that flows through
the load comes out from the bridge at the sense output. An external
resistor (RSA; RSB) allows one to detect the intensity of this current.

Input Stage. Each bridge is driven by means of four gates, the input
of which are In1; In2; EnA and In3; In4; EnB. The In inputs set the
bridge state when the En input is high; a low state of the En input
inhibits the bridge. All the inputs are TTL compatible.

Suggestions. A noninductive capacitor, usually of 100 nF, must be
foreseen between both Vs and Vss to ground as near as possible to
GND pin. When the large capacitor of the power supply is too far from
the IC, a second smaller one must be near the L298. The sense resis-
tor, not of a wire wound type, must be grounded near the negative pole
of Vs that must be near the GND pin of the IC. Each input must be con-
nected to the source of the driving signals by means of a very short
path.

Turn on and turn off: Before you can turn on the supply voltage and
to turn it off; the enable input must be driven to the low state.

Applications. The external bridge of diodes D1 to D4 is made of four
fast recovery elements (trr 3 200 n) that must be chosen from a VF as
low as possible at the worst case of the load current. The sense output
voltage can be used to control the current amplitude by chopping the

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