Build a Speech Recognition Circuit

In the near future, speech recognition will become the method of choice for controlling appliances, toys, tools, computers and robotics. There is a huge commercial market waiting for this technology to mature.

This article details the construction and building of a stand alone trainable speech recognition circuit that may be interfaced to control just about anything electrical, such as; appliances, robots, test instruments, VCR's TV's, etc. The circuit is trained (programmed) to recognized words you want it to recognize.

Speech Recognition Circuit

To control and command an appliance (computer, VCR, TV security system, etc.) by speaking to it, will make it easier, while increasing the efficiency and effectiveness of working with that device.

At its most basic level speech recognition allows the user to perform parallel tasks, (i.e. hands and eyes are busy elsewhere) while continuing to work with the computer or appliance.

This circuit allows one to experiment with many facets of speech recognition technology.

The heart of the circuit is the HM2007 speech recognition integrated circuit. The chip provides the options of recognizing either forty .96 second words or twenty 1.92 second words. This circuit allows the user to choose either the .96 second word length (40 word vocabulary) or the 1.92 second word length (20 word vocabulary). For memory the circuit uses an 8K X 8 static RAM.

The chip has two operational modes; manual mode and CPU mode. The CPU mode is designed to allow the chip to work under a host computer. This is an attractive approach to speech recognition for computers because the speech recognition chip operates as a co-processor to the main CPU. The jobs of listening and recognition doesn't occupying any of the computer's CPU time. When the HM2007 recognizes a command it can signal an interrupt to the host CPU and then relay the command code. The HM2007 chip can be cascaded to provide a larger word recognition library.

The SR-07 circuit we are building operates in the manual mode. The manual mode allows one to build a stand alone speech recognition board that doesn't require a host computer and may be integrated into other devices to utilize speech control.


  • Command and control of appliances and equipment
  • Telephone assistance systems
  • Data entry
  • Speech controlled toys
  • Speech and voice recognition security systems

Software Approach

Currently most speech recognition systems available today are programs that use personal computers. The add on programs operate continuously in the background of the computers operating system (windows, OS/2, etc.). These programs require the computer to be equipped with a compatible sound card. The disadvantage in this approach is the necessity of a computer. While these speech programs are impressive, it is not economically viable for manufacturers to add full blown computer systems to control a washing machine or VCR. At best the programs add to the processing required of the computer's CPU. There is a noticeable slow down in the operation and function of the computer when voice recognition is enabled.

Learning to Listen

We take our ability to listen for granted. For instance we are capable of listening to one person speak among several at a party. We sub-consciously filter out the extemporaneous conversations and sound. This filtering ability is beyond the capabilities of today's speech recognition systems.

Speech recognition is not speech understanding. Understanding the meaning of words is a higher intellectual function. Because a computer can respond to a vocal command does not mean it understands the command spoken. Voice recognition system will one day have the ability to distinguish linguistic nuances and meaning of words, to "Do what I mean, not what I say!"

Build Your Own Speech Recognition Circuit page 2 "Speaker Independent / Speaker Dependent