Images Scientific Instruments Inc.

Training the HM2007 IC

Clearing the memory

To erase all the words in the RAM memory (Training) press "99" on the keypad then press the "*" key. The display will scroll through the numbers 1-40 quickly, clearing out the memory.

To erase a single word space press the number of the word you want to clear, then press the "*" key.

Circuit Construction

The schematic is shown in figure 1. Three PCB boards are available for this project, see parts list. The components are mounted on the top side of the board, see Figure 3. Begin construction by soldering the IC sockets on to the PC boards. Next mount and solder all the resistors. Now mount and solder the 3.57 MHz crystal and red LED. The long lead of the LED is positive. Next solder capacitors and 7805 voltage regulator. Solder seven the seven position headers on the keypad to main circuit board as shown in figure 2 and 3. Next solder the 10 position headers on the display board and main circuit board.

Figure 3

Figure 3

Independent Recognition System

This demo circuit allows you to experiment with dependent as well as independent systems. The system is typically trained as speaker dependent. Meaning the voice that trained the circuit also uses it.

To train the system for speaker independent recognition (Multi-user) use the following technique. We will use four word spaces for each target word. Let's arrange the words so that the words can be recognized by just decoding the lest significant digit (number) on the digital display.

To accomplish this word spaces 01, 11, 21 and 31 are allocated to the first target word. By only decoding the least significant digit number, in this case 1 of "X" "1" (where X is any number 0 - 3) we can recognize the target word.

We do this for the remaining word spaces. For instances, the second target word will use word spaces 02, 12, 22 and 32. We continue in this manner until all the words are programmed.

If possible use a different person speaking the word. This will enable the system to recognize different voices, inflections and enunciations of the target word. The more system resources that are allocated for independent recognition the more robust the circuit will become.

There are certain caveats to be aware of. First you are trading off word vocabulary number for speaker independence. The effective vocabulary drops from forty words to ten words.

The decoding circuit that recognizes the word number and performs a function must be designed to recognize error codes 55, 66 and 77 and not confuse them with word spaces 5, 6 and 7. Our interface circuit does this.

Voice Security System

This HM2007 wasn't designed for use in a voice security system. But this doesn't prevent you from experimenting with it for that purpose. You may want to use three or four keywords that must be spoken and recognized in sequence in order to activate a circuit that opens a lock or allows entry.

CPU Mode

The HM2007 speech recognition chip is made to be connected to a host computer system. Actually connecting the chip to the IBM PC bus, parallel port or serial bus isn't a problem. However the circuit will require driver software needed for control training, storing and recognition. The programming will present more of a challenge than the circuit.

For anyone wanting to interface the HM2007 to a PC bus I recommend purchasing the additional HM2007 data sheet.

Kit available from us. See the kit in the online catalog.

Speech Recognition Circuit & Interface Kits

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