OPERATIONS
The circuit is powered from a 9volt battery that is
connected to an ON Semiconductor NCV7805 Positive Voltage Regulator to limit
& stabilize the board voltage to +5.0volts. all ICs are powered from this
regulated +5.0volts with the SRAM also having an additional backup CR2032
+3.0volt button battery. The CR2032 allows the main power to be shut off, while
retaining all the neural network memory in the SRAM chip & not requiring the
circuit to be re-trained each time the units is shut down. The microphone &
the keypad consist of the only user interfaces with the circuit. The microphone
is standard PC microphone which acts as the transducer converting the pressure
waves to an electrical signal. The microphone is coupled to the HM2007 IC which
is attempting to classify each word into the different trained categories. The
keypad consists of 12 normally-open momentary contacts switches. These were
soldered onto a printed circuit board which was used to communicate with the
HM2007 IC. The keypad allowed the user to train the system & also clear the
memory. The circuit outputs consist of the two 7-segment display & the LED.
The 7-segment display shows any error codes, show the target being trained
& the final classification by the HM2007system. As designed in the circuit,
the top display is the most significant & the bottom is the least
significant. For example, the number 9 would show a 0 on the top display &
a 9 on the bottom display. Only 01 through 08 was used for this project. The
LED is connected to the HM2007 IC & is used to show the status of the
HM2007 IC. When the LED is on, the system is listening & will classify all
incoming sounds. When the LED is off, the system has been placed in training
mode, and when the LED flashes, it indicates that the word spoken was just
successfully trained & placed into memory. The core component of this
project was the HM2007 LSI circuit manufactured by Hualon Microelectronics
Corporation.
This is complementary metal-oxide-semiconductor (CMOS) voice
recognition chip that contains an analog front end, voice analysis, recognition
process via neural network, and system control functions. The SRAM chip was a
Hitachi HM6264LP-70. It is an 8192 word by 8-bit static random access memory
with a read/write time less than 150ns. All the information from the HM2007 IC
is stored off-board onto the SRAM chip. The 74LS373 is an Octal D-Type
Transparent Latch. It is used to retain the binary-coded decimal (BCD) data from
the HM2007 on the 7-segment display. Two 4511 CMOS ICs were also used. These
are BCD to 7-segment Decoders that convert the BCD data stored in the 74LS373
to outputs capable of driving the 7-Segment Displays .One IC is used for each
of the 7-Segment Displays.