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Teach it to recognise YOUR voice! VOICE DIRECT Speech Recognition By Ross Tester As you are reading this, a spacecraft is speeding towards Mars. It will make a “soft” landing in just a few weeks. One of its scientific experiments will be to listen for, and learn any sounds made on the planet. That task will be undertaken by a very similar chip to that used in this project! September 1999  35 SEPTEMBER 1999  35 S ome projects appear so simple, yet the underlying technology is not only state-of-the-art, it’s difficult to believe. This is one such project: a voice recognition module which actually learns words, in your voice, and then recognises them when asked to do so. Think about that for a moment. The chip is not simply recognising an inbuilt vocabulary, though that is no mean feat in itself. It’s actually recognising words which YOU teach it. The words don’t have to be English. In fact, the words don’t have to be words in the true sense at all. They can be sounds. They can even be complete gibberish, just so long as the chip can recognise them and learn them. That’s one of the reasons it was chosen for the Mars project. Just imagine if they do find little green men up there – they’re not likely to have learnt the Queen’s English, are they? Seriously, though, if there are sounds to be heard, the chip will learn them. (If you’d like to know more about the Mars Microphone probe, check out the website www.sensoryinc.com/ html/mars.htm). Now, back to this amazing technology and our project. It’s all done with a purpose-designed module from Sensory, Inc, of the USA. This module, measuring just 50 x 50mm and containing a couple of ICs and a few surface-mount devices, is capable of learning, and then recognising, virtually any word – with Front (left) and rear (right) of the Sensory Inc. “Voice Direct” module, shown actual size. a few provisos such as the words not being too similar. For instance, it shouldn’t have a great deal of trouble with cat and cart but cat and mat might give it some angst. But more on this later. All that is required is the connection of power (5V DC), an electret microphone, a speaker and three switches and the module is ready for operation. In this mode, shown in Fig.1, it will ask you to say a word and then repeat it. If you say the word the same way twice, it will then ask you for the next word, and so on, up to 15 words in total. If you only want, say, three words, you simply do not respond when it asks for the fourth word and the learning mode is then terminated. When you push the “recognise” switch, it asks you to say a word. If your word is in its vocabulary, it responds by sending one of its outputs high. What you do with that output is entirely up to you. Fig.1: Sensory Inc’s suggested circuit which will recognise three words and flash a LED. We used this as a starting point for our experimenter's board. 36  Silicon Chip Just think of the applications: do you want the TV set on, or the channel changed? You can TELL the module which channel you want! Or you walk into a lift and instead of pressing a button, you tell the lift which floor you want. The lift then whisks you to your floor! The possibilities of such a system are endless! How about a robot which comes out to serve you in the restaurant, recognising your order by what you say? Gee, you could even send a system into space and land on another planet – Mars, for example. It could listen for sounds, learn them, recognise them – and maybe turn on a transmitter and tell us back on earth. . . Oh, someone has thought of that one already? Yes, it really is out of this world! The experimenter’s board As you can see from the photographs and main circuit, we have developed an experimenter’s PC board to go with the speech module. Let’s explain why. The user manual which accompanies the module suggests a circuit which lights LEDs when it recognises a word. However, they only suggested three LEDs. But we thought “there are 15 words, so why not 15 outputs?” It isn’t quite that simple, because only eight of the word outputs have their own output pins. The last seven require decoding, using combinations of the other outputs. So we added a couple of low-cost AND gates to provide all 15 word outputs. The manual also suggested a 4.5V power supply using three 1.5V batteries. But it also says that low battery levels will degrade performance. For the sake of a cheap 5V regulator and a couple of capacitors, we sidestepped that problem. You can use a 12V plug- pack supply without worries. Now that we had 12V available, we thought it would be a good idea to provide a relay output and driver, just in case you had something you wanted to control. Naturally, this (just like the extra decoding) is entirely optional – if you want to save a little money, you can leave them off. Some parts which aren’t optional, though, are the microphone, the speaker and the three pushbutton switches. These are, as you might expect, essential for setting the mode, teaching the module and recognising the words. Because we had now decided to put all this on a printed circuit board, we decided to mount the speaker and mic on-board and use PC board-mounting switches as well, making the whole thing self-contained. Now, how to mount the module itself? Sensory suggest using standard 0.1in header pins to make connection, as all connections to the module are brought out to holes on a standard 0.1in grid. We took advantage of this to mount the board by duplicating the rows of holes, allowing the module to simply drop over rows of header pins mounted on our PC board. From there, it was a simple matter to solder the pins to their appropriate connections – it’s impossible to get the connections wrong. (But you can bridge between adjacent pins so you have to be very careful and use a clean, fine-tipped soldering iron). As you can see, we also added two extra rows of header pins to enable connection between the word 1-8 outputs and the decoding circuitry. As output 8 is always part of the decoding, this was wired directly on the PC board. One other pair of header pins was installed on two pads which are actually shorted out. This might seem a little strange but these pins can be used to select a “slave” mode of operation if the copper between them is cut. Again, you may care to leave these pins out. All of the electronics are on a PC board measuring 160 x 118mm. Power connection to the board is made via a 2.1mm DC power socket (so it will suit most plug packs). Polarity is the “standard” centre positive but Above: the SILICON CHIP experimenter’s board ready for theVoice Direct module. The lower row of LEDs light when words 1-8 are recognised. With suitable connections the upper row of LEDs light with words 9-15. Below: with the Voice Direct module fitted. because there really is no standard, a series diode will prevent catastrophes if power is connected with the wrong polarity. A resistor and LED between +12V and 0V will show that power is on and also connected the right way around! Construction Start with the resistors. Once these are soldered in place (particularly the ones in series with LEDs), the chances of making an error in placing other components are significantly reduced. Next, solder the 9 PC pins in place. The two power diodes, small (bypass) capacitors and the two wire links complete most of the low profile components. Now move on to the semiconductors: all of the LEDs except the “power on” LED are oriented with their cathodes (marked by a flat on the body and a shorter lead) towards the edge of the board. How far down you mount the LEDs is up to you – we left about 5mm between the top of the board and the LED body. September 1999  37 You could solder them in anywhere from flat down on the board to standing full length upright (the latter has the advantage of being able to be used again in another project). The 5V regulator is mounted with its flat side towards the edge of the board and both electrolytic capacitors have their negative sides towards the edge also. The two ICs have their notched end (or the dot marking pin 1) towards the middle of the board. When mounting the switches, ensure that their flat sides also go towards the edge of the board, like the LEDs. The relay cannot mount incorrectly – it has eight pins and they only fit one way. Likewise, the DC power socket must be correct with its three pins in a triangular pattern and the opening towards the outside of the board. About all that are left are the microphone and speaker, along with the header pins which mount the module. First, the electret microphone insert. Take a look at the two pins on the rear: one of the two is connected to the case and this pin goes into the hole closest to the regulator. The speaker is mounted by two short lengths of tinned copper wire connecting the speaker terminals to the appropriate PC pins. We made our speaker more secure by putting a dab of super glue gel on the back of the speaker, securely holding it to the PC board (double-sided adhesive foam tabs would be just as effective). Finally, we come to the header pins which are used to mount the Voice Direct module. We used two 25-pin headers which gives 50 pins – exactly the number required to fill all the holes on the board. In truth, this is a bit of an overkill because in this application only 22 of the pins are actually needed to connect to the board. However, we filled all 50 holes on the base PC board with header pins and soldered only those required – 19 along one edge and three adjacent. Because the header pins come in 25-pin strips, you will have to cut them (a pair of sharp sidecutters is fine). Cut a 19-pin length from one strip and an 18-pin length from the other – these are for the parallel rows. You will have a 6-pin and a 7-pin length left from each strip; by sheer fluke there are 13 pins required to complete the set! Push the short length of the header pin block through the PC board and very carefully solder the required pins underneath using a fine-tipped iron with a clean tip. Regularly clean the tip on a wet sponge as you work and don’t overheat the solder joint as the pads are very small and could easily lift. Check, and check again, that you haven’t bridged solder between any two pins. We didn’t bother soldering all 50 pins in place on the board, only the required pins (ie, all 19 in one strip and the three adjacent) and also the end pins of each of the other header pin sets, just to hold them in place. An 8-pin length and a 7-pin length of header pins are also needed to connect the chip outputs and decoding lines. We also used a 2-pin set on the pads connected to the “stand alone” pins but this is not necessary in this application (we happened to have a Fig. 2: our final experimenter’s board circuit. You can see the similarities between this circuit and the basic circuit overleaf. We have added a power supply, outputs for all words and also some decoding for words 9 through 15. 38  Silicon Chip HEADER PIN SET JP3 – PINS 12-14 CONNECTED HEADER PIN SET JP1 – NO CONNECTION HEADER PIN SET JP2 – ALL CONNECTED EXCEPT 8 & 9 Fig 3: Here's how it all goes together on the printed circuit board. The bottom row of LEDs represents words one to eight while the top row will decode nine to fifteen. The word output pins 1-7 need to be connected to the appropriate word 9-15 input pins for decoding – see the separate logic table. 2-pin set spare, so why not?) You could use a single header pin (instead of a PC stake) in the base circuit of the relay driver if you wish. Before mounting the Voice Direct module on the PC board, you might like to confirm that the everything is working correctly. Plug in a 12V supply and ensure that the power LED lights. Measure the voltage between pins 4 and 5 of header pin set JP2 of the voice module (counting from the end closest to the supply) and confirm it is 5V (pin 4 +5V, pin 5 0V). Temporarily solder a length of insulated hookup wire to a point on the +5V rail under the board and touch the other end of this lead on each of the header pins in the 8-pin set (word 1-8 outputs). Each of the LEDs should light in turn. Do the same with the 7-pin row (word 9-15 inputs) and each of those LEDs should also light. Finally, touch the lead on the PC stake (or header pin) connected to the base circuit of the relay driver and you should hear the relay click in. If all is OK, disconnect power and unsolder the wire. If all is not OK, you’ll need to track down the fault before proceeding. There are four holes on the board (above the switches) which at this stage we’ll leave unfilled. They’re for a more difficult learning mode, which we’ll cover shortly. Mounting the module With the header pins in place, it is simply a matter of dropping the Voice Direct module over the pins and sliding it down. Because the holes on the module are all plated through, it is quite possible that the module won’t even need to be soldered in place (especially useful if you wish to use the module elsewhere). But . . . Murphy’s law being what it is, there is always a chance that one or more pins won’t make contact so we took the safe way out and soldered the 22 required header pins to the module. Again, a very fine, clean iron is essential. The project is now finished: now’s the time to teach it some words! Voice “training” Apply power to the board and press the “train” button. You should hear a voice say “Say word 1”. Speak your chosen word clearly into the microphone. The voice will say “repeat”. Make sure you speak the same way – that is, don’t change inflections or emphasis because the module may think you are saying a different word. If it understands the word, it will say “accepted” and ask you to “say word 2”. You keep on repeating the process until all 15 words are trained or you have trained the number of words required. If you want to train six words, for example, simply do nothing when it asks you for word seven and it will respond with the September 1999  39 Parts List 1 PC board, code 07109991, 160 x 118mm 1 Sensory Inc. “Voice Direct” speech recognition module 1 2.1mm PCB mounting DC power socket 3 25-pin 0.1in header pin sets 3 momentary action push button switches, PC board mounting 1 PC board mounting 12V relay, DPDT contacts 1 electret microphone insert 1 8Ω speaker, 57mm Semiconductors 16 5mm LEDs (any colour) 2 4081 quad AND gate ICs 1 BC337 NPN transistor 1 7805 voltage regulator 2 1N4004 power diodes Capacitors 1 1000µF 25VW PC electrolytic 1 10µF 12VW PC electrolytic 2 0.1µF MKT polyester, monolithic or ceramic Resistors (0.25W, 5%) 2 10kΩ   1 1kΩ 15 560Ω Miscellaneous 9 PC stakes, hookup wire for links, header cables for connecting module outputs to decoder inputs words “training complete”. If a chosen word is too close to another word, it will tell you. You should try to avoid similar sounding words. There is a way to ensure stricter training and recognition which we will cover shortly. If you have any difficulty getting the module to recognise words, a few tips: •  Keep the same distance from the microphone with the same voice level when training and saying words. •  Use a natural voice – while the module will remember accents and strange voices, you might not! •  The physical and emotional state of the voice matters. For example, if you’ve just run up a flight of steps and are out of breath, your voice will sound different than when you are relaxed. •  In either training or recognition, 40  Silicon Chip background noise may be a problem – the module doesn’t know that the background noise is not part of the word! So take this into account. Voice recognition Press the “recognise” button and you will be asked to say a word. Say the word clearly. If the module recognises the word it will respond with the appropriate word number and light the LED corresponding to that number. If it cannot recognise the word because of incorrect pronunciation, inflection or accent, it will say “word not recognised”. If you say the word too softly it will ask you to speak up. If you say the word too quickly it will tell you so! As described, the module is set up for “relaxed” training – it will recognise more words but may not be able to differentiate between some words. Another mode, called “strict” training and recognition, is also available. In this mode, where the train and recognise lines are permanently pulled to ground via a 100kΩ resistor, the module is harder to train, it accepts less words but has better accuracy in recognising words. Provision has been made on the PC board for these 100kΩ resistors – they’re the empty holes we referred to earlier above the train and recognise switches. For most purposes, the relaxed mode is easier to use – in this case, simply leave the 100kΩ resistors out. Decoding As mentioned before, words 1-8 cause a single output to go high for about a second, lighting the appropriate LED. Words 9-15 need to be decoded because they send two outputs high – output 8 and another of the 1-7 outputs, depending on the word. Table 1 shows the output table. In order to differentiate between words 1-8 and 9-15, decoding is required. We have provided two 4081 quad AND gates on the board with the module output 8 permanently connected to one input from each gate. Decoding, then, is simply a matter of connecting a wire between the appropriate 1-7 output header pin and the required decoder header pin. This will cause a single LED to light for outputs 9-15. Logically, word 9 would be the LED closest to the PC board corner and word 15 would be the LED closest to the speaker. Relay output A relay circuit is also provided to give a “real world” output, with two sets of changeover contacts. Usage is simple: connect the relay driver input to any of the required word outputs and when that word is recognised, as well as its LED lighting the relay will pull in for the same time. This is about a second which should be long enough to initiate some further action. If not long enough, a simple time delay can be added. Note that we have not provided any latching circuitry on the PC board – if you want this, it can easily be achieved by using one of the sets of relay contacts to hold the relay on once it is triggered. TABLE 1: WORD RECOGNITION LOGIC Word 1 Word 2 Word 3 Word 4 Word 5 Word 6 Word 7 Word 8 Word 9 Word 10 Word 11 Word 12 Word 13 Word 14 Word 15 Output 1 (header pin set JP2 - pin 12) Output 2 (pin 13) Output 3 (pin 14) Output 4 (pin 15) Output 5 (pin 16) Output 6 (pin 17) Output 7 (pin 18) Output 8 (pin 19) Output 8 (pin 19) AND Output 1 (pin 12) Output 8 (pin 19) AND Output 2 (pin 13) Output 8 (pin 19) AND Output 3 (pin 14) Output 8 (pin 19) AND Output 4 (pin 15) Output 8 (pin 19) AND Output 5 (pin 16) Output 8 (pin 19) AND Output 6 (pin 17) Output 8 (pin 19) AND Output 7 (pin 18) Where do you get the Voice Direct Module? At the time of going to press, we were unable to determine if distribution has been arranged in Australia. It is possible that some suppliers will have stock shortly. These days, though, there is no great problem as it is possible to buy the module direct from the USA using the Internet. Sensory Inc. distributors Jameco Electronic Components (www.jameco.com) or JDR Computer Products (www.jdr. com) have a kit available for $US49.95 plus postage and handling. This kit includes three tiny pushbutton switches (not the same as the Jaycar ones we used but they will fit the PC board), a speaker, microphone insert and of course the pre-assembled module itself. Apart from the PC board, all the components on our experimenter's board are commonly available. The PC board should be available from the usual PC board suppliers such as RCS Radio in Sydney. For more information on the Voice Direct module, including detailed data in Acrobat format (PDF), visit the Sensory Inc website: SC www.sensoryinc.com Following the retirement of our technical draftsman (who has been with SILICON CHIP since the first issue), we are looking for someone with the right qualifications and experience to take his place. The person we are looking for must be able to maintain the outstanding “look and feel” of the circuit diagrams, PC board overlays, drawings and diagrams which have become synonymous with SILICON CHIP and have contributed very much to its success and respect in the marketplace. Essential requirements for this position: •  An understanding of electronics, to at least advanced hobbyist level – the function, operation and requirements of components and electronic circuitry. •  Practical experience in one or more of the PC-based CAD, engineering or drawing packages used today (we use Generic CAD but other software experience will be acceptable). •  The ability to interpret a variety of original material and turn it into clear, lucid diagrams. •  The ability to handle sometimes very tight deadlines with accuracy, clarity and thoroughness. •  The ability to work as part of a small, busy team. •  The ability to commence yesterday! Other qualifications and experience which would be well regarded: •  Experience in Internet web page design and construction. •  The ability to design and produce electronic projects of the type which appear in SILICON CHIP. •  Possibly technical writing expertise. SILICON CHIP offices are located at Mona Vale on Sydney’s Northern Beaches. This is the full-size PC board pattern for the project. Because of the close spacing of tracks (especially around the header pin sockets) copying this from the magazine is not really a proposition. Use it instead to check commercially obtained boards. Of course, the PC board pattern is available from the SILICON CHIP website, www.siliconchip.com.au If you can satisfy all, or most of these requirements, please contact Leo Simpson, Publisher, SILICON CHIP with your CV as soon as possible in one of the following ways: email: silchip<at>siliconchip.com.au Fax: (02) 9979 5644 Mail: PO Box 139, Collaroy NSW 2097. September 1999  41