September
1999, Issue 110
Taking
Orders:
A
Speech Recognition Module
VoiceDirect
PROCESSOR
The
heart of this module is the VoiceDirect speech recognition
processor. The processor is available in a QFP-64 package
for anyone who needs or wants to build a circuit from
scratch.
This
module has a lot of the preliminary work already provided,
including an AGC audio amplifier, serial EEPROM, and
clock. It also contains extensive socket headers (JP1,
JP2, and JP3), which make it easy to connect an external
circuit to the module. Table 1 shows you the pinout.
| Name
|
Module |
Pin |
Description |
| |
JP1 |
1-17 |
Unused |
| |
JP2 |
9 |
Unused |
| |
JP3 |
1-9 |
Unused |
| Preamp
in |
JP2 |
1 |
Microphone
input connection |
| Mic Bias |
JP2 |
2 |
Mic bias
(electret microphone) |
| AGND |
JP2 |
3,5 |
Analog
ground–do not connect to digital ground because
of noise |
| +5V |
JP2 |
4 |
Vcc |
| PWM1 |
JP2 |
6 |
Pulse
width modulator–Output 1, connects to 8–32-Wspeaker |
| PWM0 |
JP2 |
7 |
Pulse
width modulator–Output 0, connects to 8–32-Wspeaker |
| DACOUT |
JP2 |
8 |
Analog
audio ouput–Provides better quality sound than
PWM ouput, requires amplifier |
| RECOG |
JP2 |
10 |
Recognition
sensitivity selection and activates recognition |
| TRAIN |
JP2 |
11 |
Training
sensitivity selection and activates training |
| Out1-Out7 |
JP2 |
12-18 |
Stand-alone
mode output lines 1-7 |
| High/Out8 |
JP2 |
19 |
Stand-alone
mode output lines 8/ or high |
| ERROR |
JP3 |
10 |
Stand-alone
mode error signal |
| GND |
JP3 |
11,12 |
Digital
ground, CPU core (pins 1, 33) |
| Mode |
JP3 |
13 |
Stand
alone or slave |
| Reset |
JP3 |
14 |
Vcc |
Table
1—Here you see the pinout for the module. The schematic
is given in Figure 1.
We
can best explore the capabilities of the module by getting
it up and running. The VoiceDirect speech-recognition
kit contains the module (assembled), microphone, speaker,
three microswitches, two 100-kW resistors, and a quick
setup guide (see Photo 2).
Photo1—The
kit includes the module, resistors, three push-button
switches, microphone, speaker, and manual—all
the external components you need to implement
stand-alone recognition.
|
The
module’s schematic is shown in Figure 1. The few external components that are supplied
with the kit are all it takes to get the module functioning.
The PCB measures 2² × 2² and has 0.1² header sockets
soldered to one side of the board, which makes it easy
to connect to the circuit. To experiment with the module,
I placed my external components on a solderless breadboard
(see Figure 2).
Figure 2—This test circuit schematic demonstrates
how simple it is to get the VoiceDirect module
up and running.
|
To
connect components on the breadboard to the socket headers,
I used 22-AWG stranded wire. I mounted the microswitches,
resistors, microphone, and LEDs on the breadboard.
One
note here: the schematics in the manual detail the board
shown from the top, but the header sockets are mounted
on the bottom side of the PCB. This is in contrast to
Figure 2, which shows the board with the header sockets
on top. Be careful when comparing Figure 2 to the drawing
in the manual.
The
VoiceDirect module recognizes 15 words in stand-alone
mode and has only eight outputs (connector JP2 pins
12–19). For simplicity, I’m only using eight
outputs (eight words) so I don’t need to add a
decoding circuit. The 8-pin output for the 15-word recognition
doesn’t follow the standard binary numbering (see
Table 2).
| Word 1 |
Output
1 |
| Word 2 |
Output
2 |
| Word 3 |
Output
3 |
| Word 4 |
Output
4 |
| Word 5 |
Output
5 |
| Word 6 |
Output
6 |
| Word 7 |
Output
7 |
| Word 8 |
Output
8 |
| Word 9 |
Output
8 and 1 |
| Word 10 |
Output
8 and 2 |
| Word 11 |
Output
8 and 3 |
| Word 12 |
Output
8 and 4 |
| Word 13 |
Output
8 and 5 |
| Word 14 |
Output
8 and 6 |
| Word 15 |
Output
8 and 7 |
Table
2—This table shows the digital output for 15 words
when the device is in stand-alone mode.
