Page 169 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

Microphone support
Manual and CPU modes available
Response time less than 300 milliseconds (ms)
5 volt (5V) power supply
Circuit construction
The speech-recognition circuit is available in kit form from Images
Company (see the parts list at the end of the chapter). The
schematic is shown in Fig. 7.1. The components can be mounted
and wired on a standard printed circuit board (PCB).
Solder the keypad to the board according to Fig. 7.2. You will have
just seven wires from the keypad to the HM2007 on the PCB. The
number next to each wire coming out of the keypad refers to the
pin number it’s connected to on the HM2007 IC.
Figure 7.3 shows the top view of the parts placement on the PCB.
Figure 7.4 is the complete speech-recognition circuit.
Independent recognition system
This demonstration circuit allows you to experiment with depen-
dent as well as independent systems. The system is typically
148 trained as speaker dependent, meaning the voice that trained the
circuit also uses it.
We will take the other track and train the system for speaker inde-
pendent recognition. To accomplish this we will use four word
spaces for each target word.

To simplify the digital logic, the allocation of word spaces is as fol-
lows. Our circuit will only look at the first [least significant digit
(LSD) on the display] digit space for recognition. This means that
the word spaces 01, 11, 21, and 31 will all be recognized as the
same word. Since we are only decoding the first digit, they all look
like word space 1. Likewise word spaces 04, 14, 24, and 34 all look
like word space 4.
This system works most of the time, but a problem is encountered
when an error code pops up.
55 word too long
66 word too short
77 no word match found
Obviously the base circuit would identify these error codes as
word 5, 6, and 7, respectively. There are two ways to work around
this problem. The first way is to use a dedicated logic circuit

Team LRN
Chapter seven