Page 180 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

This is how the error detector prevents numbers 55, 66, and 77
from being mistaken for words 5, 6, and 7.
When the BCD propagates through the 74LS373, it connects to the
input of a 4028 BCD-to-decimal decoder. The 4028 reads the BCD
number and outputs a logic high ( 5V) on the appropriate decimal
output line (0 to 9).
Creating a more useful output

The logic high output from the 4028 can be used to control alter-
nating current (AC) and direct current (DC) loads. However, it is
much better to run the output from the 4028 through a flip-flop
first. The reason is that the 4028 by itself will only keep one of its
outputs high at any given moment. So whenever the circuit turns
something on, whatever may have been turned on will be turned
off. Not very convenient. The flip-flop solves this problem. Once
triggered by a logic high, the flip-flop output will remain high until
a second signal (low-high) brings its output low. The result of us-
ing a flip-flop on an output line is twofold.
Primarily one can turn on and off any number of outputs without
affecting the status of any other line. Secondly, the same command
may be used to turn on (first time spoken) and then turn off (sec- 159
ond time spoken) a circuit. So instead of having two separate
on/off commands for each device (like light-on and light-off), the
same command can be used a second time to turn off the device
(light-light). In some cases this is like doubling your command
vocabulary.
Figure 7.9 shows a 4013 flip-flop circuit that may be used. Each
4013 IC has two usable flip-flops. The inputs of the flip-flops are
connected directly to the line output of the 4028.
Figure 7.10 shows one circuit and two fragments that may be con-
nected to the flip-flop for controlling different types of loads. The
circuit in A is an NPN Darlington transistor, with a DC source and
resistive load. One may also use this type of circuit to open and
close a relay, as shown in B. The relay can control AC and DC loads
(resistive or inductive). In C the output of the 4013 is connected
to an optocoupler with a Triac output.

Operation
The speech-recognition circuit is trained as described previously.
With the interface circuit connected, each word command will
light an LED or circuit, depending upon what’s connected to the
output of the 4028 BCD-to-decimal decoder chip.
Team LRN Speech-controlled mobile robot