Page 178 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

Forward
Backward
Left
Right
Stop
Sleep
On
Lock
Unlock
Stop (The command stop is so important in this application
that it may take up more that one command position.)
The first command we want to train the circuit to recognize is for-
ward. We will use the following four word spaces: 10, 20, 30, and
40. By dropping the most significant digit (MSD) of each number,
we are left with the LSD that is the same for all four word spaces,
word number 0. Similarly the next command word, backward, will
use word spaces 01, 11, 21, and 31. Dropping the MSD again, we
are left with word number 1.

The interface must recognize the word error codes and not mistake 157
them for word numbers 5, 6, and 7. The circuit uses two 4011
NAND ICs configured to operate as OR and AND gates (as shown
in Fig. 7.8) to detect the 55, 66, and 77 word errors.

Connection to speech kit

The speech-recognition kit has nine solder holes between the
74LS373 and 7448 chips for connecting an interface circuit (see
Fig. 7.8). Eight lines represent the two BCD numbers, and the
ninth pad is a ground. There is also one open pad by the red LED.
A wire soldered here is used as an input signal to a word trigger for
the interface circuit.
How it works

To begin, the interface circuit must be able to react whenever the
SRC hears a word. When the SRC hears a word, it attempts recog-
nition and the red LED blinks off momentarily.
The current to the LED is used as a word trigger. To use this as a
trigger, we set up a comparator connected to the cathode side of the
LED. The reference voltage for the comparator is set at 3.64 V using
a voltage divider consisting of two resistors, 5.6K- and 15K-ohms.

Team LRN Speech-controlled mobile robot