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As every intergalactic traveller knows, in the far reaches of our universe (and beyond) it is inevitable that you will meet up with characters that communicate using a metallic sounding voice (would Gene Roddenberry and George Lucas lie to you?). Some aliens can be highly offended and consider it an act of war if you don’t answer them in their own voice – and now you can, thanks to the SILICON CHIP Galactic Voice. Use it for an instant rapport with all the beings that you meet in your travels. by JOHN CLARKE Galactic Voice W E’VE ALL SEEN and heard those sci-fi TV programs and films which include characters – either real “living” beings or fully robotic ’droids – that speak with electronic sounding voices. The living beings are often heavily modified with mechanical and electronic prosthetic devices. The modifications extend to voice changing headpieces designed to cause menacing expressions. The voice changing tends to bring 66  Silicon Chip out the worst evil features from the characters. Some examples of characters from the galaxy with metallically challenged voices (and with bad attitudes!) include the Droids from “Star Wars”, the Cylons from “Battle Star Galactica” and the Daleks from “Dr Who”. Who could not resist holding their arm out and saying “Exterminate, Exterminate, we are the Daleks” especially when armed with a metallicsounding voice? Each of these characters has their own distinctive voice signature and the SILICON CHIP Galactic Voice includes controls to match the required character. Imitating the voices is as simple as switching on the Galactic Voice and speaking in a normal voice into an inbuilt microphone. The electronics and the loudspeaker do the rest for you, converting your normal, totally boring voice into a metallically accented diabolical one. siliconchip.com.au Just add your voice and you too can sound like a Klingon, Dalek, a Droid, a Cylon . . . you name it! There is an “effect” control which changes the metallic effect by changing the pitch of the metallic sound from a high through to a low pitch. There is also a “depth” control, which adjusts the amount that the metallic sound is impressed upon your voice, from a relatively normal voice through to a fully metallic voice. A volume control sets up just how much sound you can deliver to your fearful audience. The maximum overall volume is similar to that produced by your own voice when speaking normally. Too much volume will cause feedback between the microphone and loudspeaker and produce a loud squeal. the Galactic Voice. Signal from the microphone is amplified by IC1 and sent to a mixer, IC3. This combines the amplified signal with a square wave carrier signal produced by variable frequency oscillator IC2. The frequency of oscillation is set by the “Effect” control, while the “Depth” control sets the amount of signal that is applied to the mixer. Output from the mixer is the carrier signal produced by the oscillator but with the level of this signal following the shape of the amplified microphone waveform. As could be expected this significantly changes the way the signal sounds – the sound produced is simi- How it looks The Galactic Voice unit comprises a 120mm long, flared plastic tube with a loudspeaker mounted inside the flared end. The controls are located at the opposite end of the tube. This end is held close to the mouth so that you can speak directly into the microphone. A power switch is used to switch the Galactic Voice on or off and a LED indicates when power is on. How it works Fig.1 shows the block diagram for siliconchip.com.au lar to the metallic sounding voices we know so well. The resulting metallic voice sound is applied to the power amplifier (IC4) via the volume control (VR3). The waveforms overleaf show the results of the modulation where the oscillator signal is mixed with the amplified audio signal from the microphone. The waveform at top is the amplified signal from the microphone, while the lower waveform is the signal after the mixing. The signal shown is taken from the power amplifier output. You can see that this signal is the oscillator waveform modulated in level according to the microphone signal. AMPLIFIER IC1 SIGNAL MIXER IC3 MICROPHONE MODULATED CARRIER VOLUME VR3 CARRIER DEPTH VR1 OSCILLATOR IC2 POWER AMPLIFIER IC4 LOUDSPEAKER EFFECT VR2 Fig.1: the block diagram of the SILICON CHIP Galactic Voice. Compare the functional blocks with the circuit diagram overleaf. September 2006  67 Fig.2: the microphone signal is amplified by IC1, then mixed with a variable square wave from IC2 to produce a modulated square wave, as shown below. IC4 further amplifies the signal to drive a small loudspeaker. The circuit The circuit has just four low-cost ICs, two other semiconductors, three potentiometers, a microphone, a loudspeaker and a few other components. We’ll start with the electret microphone. These types of microphones require a power supply; in our case it is derived from the main supply rail via a 1kW decoupling resistor and a 10kW limiting resistor. This supply is filtered with a 100mF capacitor to minimise any voltage fluctuations on the main supply (which would happen as the amplifier works hard) from being passed into the sensitive microphone circuitry. Signal from the microphone is ACcoupled to the non-inverting input of The top waveform is the voice signal, amplified after being received by the microphone. The bottom waveform is at the audio amplifier and shows the carrier signal modulated by the to p waveform 68  Silicon Chip amplifier IC1a, half of an LM358 (the other half is not used). It has a gain of about 13, set by the 470kW resistor between pins 7 and 6 and the 39kW resistor at pin 6. The 33pF capacitor rolls off the amplification above 10kHz to prevent possible oscillation in the amplifier. IC1a is biased at close to half the power supply voltage via two 220kW resistors connected as a voltage divider across the nominal 8.7V supply. (We’ll explain why it is 8.7V shortly). The resulting 4.35V nominal supply is filtered with a 100mF capacitor. The idea of biasing IC1a at this nominal 4.35V is so that the output is able to swing symmetrically above and below this voltage. Before we look at where the output goes, let’s turn our attention to the carrier oscillator, IC2. This IC is a CMOS version of the famous 555 timer and is used because it draws far less current than the standard version. The timer is connected to produce a continuous square wave signal and operates as follows: Pins 2 and 6 are the threshold inputs that monitor the 100nF capacitor voltage. This capacitor is charged and discharged via the siliconchip.com.au Fig.3: here’s how to put it all together – this diagram matches the photo below. The triangular PC board at the right end mounts vertically onto the four PC pins. This board needs a little “surgery” first to fit the nut and screw. variable resistance VR2 and the 1kW resistor, via the output at pin 3. When charging, pin 3 is high (at the supply voltage) and the capacitor voltage rises. When the voltage reaches 2/3 the supply voltage (detected by the input at pin 6), pin 3 goes low (at 0V). The 100nF capacitor now discharges until the voltage reaches 1/3 the supply voltage (detected at pin 2). Pin 3 goes high again to recharge the capacitor. The process continues and a square wave is produced at pin 3. The frequency can be set from 655Hz and 7.2kHz by varying VR2. Potentiometer VR1, connected between the pin 3 output of IC2 and the 8.7V supply rail, provides control over the carrier level. With the wiper of VR1 wound fully toward the 8.7V end, there will be no output signal. As VR1 is wound down, increasing amount of square wave from pin 3 will pass through, with full signal available when the wiper is turned fully toward the pin 3 end of the potentiometer. VR1 therefore provides a depth control of the modulation. The 100kW resistor in series with the wiper limits the modulating level to a maximum of around 50mV, thus preventing overload at the maximum setting of VR1. Into the mixer The output of IC1, taken from pin siliconchip.com.au 7, is AC-coupled to the signal + input of the mixer (IC3) at pin 1. The signal – input (pin 4) is coupled to ground via a 10mF capacitor. Because of this, signal is only applied to the signal + input. At the same time, the output from IC2, taken from pin 3 via the depth control, is AC-copuled to the CARinput (pin 10), with the CAR+ input (pin 8) also AC-coupled to ground. There are three 1kW resistors forming a resistive divider between the 8.7V supply rail and ground. Pins 1 and 4 of IC3 connect (via 1kW resistors) to the lower resistor in this divider. VR4 allows the circuit to be balanced. Balancing removes the carrier signal from the mixer output when there is no applied signal at the signal + input. The carrier signal is applied to the pin 10 input, which is biased to the top 1kW resistor in the divider string and the voltage is decoupled with a 100mF capacitor. The carrier + input is also fixed at this bias voltage. The mixer outputs (pins 6 and 12) are biased with 3.3kW resistors to the 8.7V supply. The 10kW resistor from pin 5 of IC3 sets the overall bias of the mixer and the 1kW resistor between pins 2 and 3 set the mixer gain. Output from the mixer (pin 6) is coupled via a 1mF capacitor to the This photo, reproduced close to life size, shows the populated PC board before the battery holder is screwed onto the three standoffs (the white hexagonal pillars). The M4 screw (right end) would normally not be inserted until after the assembly is placed inside its plastic tube “case” – we left it there ’cause we didn’t want to lose the screw! September 2006  69 This shows how the support PC board is attached to the main board. . . The completed assembly, ready to slide into the speaker port tube. The two apparently unused PC stakes at the very left of the board are for the control panel LED and are actually soldered to underneath the PC board. . . . while this shot shows the underside of the control panel with power switch and LED. volume control, VR3. This adjusts the level of signal applied to the power amplifier, IC4. The amplifier drives the 8W loudspeaker, via a 100mF capacitor which blocks the DC component from IC3’s output. The 10W and 47nF capacitor at IC4’s output provides a substantially capacitive load at higher frequencies to prevent the amplifier from oscillating. The main supply is therefore a nominal 8.7V, due to the 0.3V drop across D1. LED1 is included to indicate whenever power is on. Overall current drain is less than 14mA with a 9V battery, which should give about 300 hours of battery life with a fresh alkaline battery and intermittent use. Protection The circuit is powered by a 9V bat- tery, controlled by power switch, S1. As you no doubt realise, it is far too easy to reverse-connect a 9V battery, which can – and often does – let the smoke out of semiconductors. So diode D1 prevents current flow if the battery is connected the wrong way around. The diode deserves special mention: it is a Schottky type, not a normal silicon variety. Schottky diodes have a voltage drop about half that of silicon diodes (0.3V vs 0.6V), thereby maximising battery life. Construction Most components for the Galactic Voice are assembled onto a 93 x 55mm PC board, coded 08109061. A second trapezoid-shaped 34 x 55mm PC board, 62mm GRILLE DISC M4 SCREW THROUGH PORT AND INTO NUT ELECTRET MIC IN GROMMET 10mm LONG M3 CSK HEAD SCREWS 9V BATTERY HOLDER M4 NUT SOLDERED TO PC BOARD SUPPORT PC BOARD 15mm LONG M3 TAPPED SPACERS MAIN PC BOARD CONTROL PANEL (58mm ALUMINIUM DISC) S1 S1 A LED (BEHIND SWITCH) 6mm LONG M3 NYLON SCREWS K HEATSHRINK INSULATION 70  Silicon Chip LOUDSPEAKER CEMENTED ONTO GRILLE DISC WITH SILICONE SEALANT FLARED LOUDSPEAKER PORT Fig.4: the whole assembly slides into the speaker port “case” from left to right (the speaker “baffle” disk is already glued in place with silicone sealant). Take care that you don’t crimp or catch the speaker wiring (which is actually much longer than shown here) as you slide it in. When in the right place, the control panel will be right at the open end of the port tube and the M4 nut will be level with the hole in the port side, ready for the M4 screw to be inserted and tightened. siliconchip.com.au coded 08109062, is used as a support for the assembled project. An M4 nut is soldered to the top of the support PC board, with a matching hole drilled near the flared end of the tube. An M4 screw passes through this hole into the nut, securing the Galactic Voice components in place within the tube. The assembled PC board is housed in a flared plastic speaker port tube measuring 58mm diameter x 120mm long. An aluminium disc is used as the support for the loudspeaker and is secured to the flared end of the tube using silicone sealant. This is 62mm diameter and has holes drilled to make a speaker grille (see Fig.5b). The opposite end of the tube has a similar, though smaller, aluminium disk (58mm diameter) drilled to accept the potentiometers, the switch and LED bezel and for the microphone mounting grommet (Fig.5a). Begin construction by checking the main PC board for any shorts or break in the tracks. Defects in boards these days are rare but if you find any, repair them now to avoid problems at a later stage. Shorts between tracks can be fixed by scraping between the tracks with a sharp hobby knife. Breaks in tracks can be connected with a layer of solder, with a short length of wire acting as a bridge if necessary. Insert the low-profile components first such as the links, the diode, the resistors and the ICs. Use the resistor colour code table to help find each value of resistance, and/or check the value using a digital multimeter. Take care when installing the polarised components (eg, all semiconductors and ICs and electrolytic capacitors) that they are oriented correctly and in the correct position. Solder the components in position and cut the pigtails from the resistors and link from the underside of the PC board with fine, sharp sidecutters. Now insert the PC stakes. These are located at all the external wiring points and at the four mounting points for the second PC board, at the right hand edge of the main PC board. Finally, solder in all other on-board components. Before installing the pots, cut the shafts to length to suit the knobs you are using. Now install the pots taking care to place the log potentiometer in the volume position. siliconchip.com.au Parts List – Galactic Voice 1 PC board coded 08109061, 93 x 55mm 1 PC board coded 08109062, 34 x 55mm 1 “Galactic Voice” panel label 58mm in diameter 1 flared speaker box port 58mm inside diameter x 120mm long (Jaycar CX-2688 or equivalent) 1 57mm diameter 8W loudspeaker 1 miniature electret microphone insert 1 1mm aluminium disc, 62mm diameter 1 1mm aluminium disc, 58mm diameter 1 9V PC mount battery holder 3 knobs to suit potentiometers 1 SPDT toggle switch (S1) 1 rubber grommet with 9.5mm ID hole 1 5mm LED bezel clip 3 M3 tapped x 15mm spacers 3 M3 x 10mm countersunk screws 3 M3 x 6mm Nylon screws (or cut down longer screws) 1 M4 x 15mm screw and nut (brass preferable – see text) 1 50mm length of single core shielded cable 1 400mm length of medium duty hookup wire 1 200mm length of light duty figure-8 speaker wire 1 50mm of 3mm heatshrink tubing 1 60mm length of 0.7mm diameter tinned copper wire 1 150mm cable tie 15 PC stakes Semiconductors 1 LM358 dual op amp (IC1) 1 7555 CMOS 555 timer (IC2) 1 MC1496 balanced mixer (IC3) 1 LM386 1W power amplifier (IC4) 1 1N5819 Schottky Diode (D1) 1 5mm red LED (LED1) Capacitors 1 470mF 16VW PC electrolytic 4 100mF 16VW PC electrolytic 4 10mF 16VW PC electrolytic 1 1mF 16VW PC electrolytic 1 220nF MKT polyester 2 100nF MKT polyester 2 47nF MKT polyester 1 33pF ceramic Resistors (0.25W 1%) 1 470kW 3 220kW 1 100kW 1 39kW 2 10kW 2 3.3kW 1 2.2kW 9 1kW 1 10W 2 10kW linear 16mm PC mount potentiometers, (VR1,VR2) 1 10kW log 16mm PC mount potentiometer (VR3) 1 50kW multi-turn top adjust trimpot (VR4) Miscellaneous Silicone sealant (non-acid cure), black paint The pots must be earthed to the 0V rail on the PC board with a linking wire from the 0V PC stake soldered to each pot body. The coating on the pot does not take solder easily – almost certainly, you will need to scrape it away where it is to be soldered to ensure a good attachment for the wire. The hardware The PC board requires cutouts to allow the M4 nut to be soldered to the PC board and also a notch to allow September 2006  71 (Left): this view shows the business end of the Galactic Voice with a small speaker glued inside the ‘grille’. The ‘case’ is a Jaycar speaker tuning port which just happens to be the right size! (Right): here’s the opposite end. The microphone is located inside the grommet (top) while the three controls are effect, depth and volume. The LED shows that power is switched on. the matching M4 screw to insert into and through the nut. These cutouts are the non-copper areas shown on the PC board. They can be cut out with a drill and hacksaw and finished with a file. Solder a brass M4 nut to the top edge of the support PC board as shown. When you solder the nut onto the PC board make sure the inside thread is not soldered. Fig.5 shows the holes and sizes for the control panel and the speaker “grille” discs. These are made from 1mm aluminium sheet offcuts. Cut out the circle shapes with tinsnips or a hacksaw and file to shape. The front (62mm) disc requires a series of holes, as shown, to allow the sound to escape from the loudspeaker. We painted the outside face of our grille black using a spray can. When the paint was dry, the loudspeaker was secured to the grille with a smear of silicone sealant around the speaker rim. Wire up the loudspeaker using 170mm of mini figure-8 speaker wire and secure it around the magnet on the loudspeaker with a cable tie. This will ensure a tug on the wires doesn’t break off the lugs on the loudspeaker. Attach the speaker grille and loudspeaker assembly to the inside of the flared end of the port using silicone sealant. If you are building from a kit, the disc at the opposite end, the control panel, may already be pre-punched and screen-printed. If not, attach the panel label (Fig. 6) to the control panel and cut the holes out through the panel with a sharp knife. Place the power switch, the LED bezel and LED in position and insert the rubber grommet in the microphone hole. Wire the microphone using the shielded cable and then insert the 62 DIAMETER 9 B 58 DIAMETER A A 19 A 19 10 C 34 D 10 Fig.5a CONTROL PANEL CL 72  Silicon Chip microphone into the rear of the grommet. Attach the control panel to the PC board and secure it using the potentiometer nuts. Solder the microphone lead to the top side of the PC board (PC stakes) and the LED and switch direct to the appropriate copper pads on the underside of the PC board. The 9V battery holder is mounted on 15mm long‑ standoffs and with M3 screws as shown in Fig.4. The three mounting holes in the battery holder are drilled out to 3mm (or 1/8”) and counter-bored to suit the M3 countersunk screws. Nylon screws are used beneath the PC board to prevent shorting the tracks. They can be cut down to 6mm using side cutters. Before mounting, bend the output terminals inward flat against the underside of the holder and solder hookup wire to each terminal. Now attach the holder in place. HOLE DIAMETERS: A: 7.0 B: 12.0 C: 6.0 D: 6.5 E: 5.0 ALL DIMENSIONS IN MILLMETRES E E E E E E E E E E E E E E E E E E E E E Fig.5b LOUDSPEAKER GRILLE The drilling detail for the front (control) panel (Fig.5a, left) and the rear (speaker baffle) panel (Fig.5b, right). Note that these 1mm aluminium disks are different sizes. siliconchip.com.au Resistor Colour Codes o o o o o o o o o No. 1 3 1 1 2 2 1 7 1 Value 470kW 220kW 100kW 39kW 10kW 3.3kW 2.2kW 1kW 10W Checkout time EFFECT DEPTH VOLUME Galactic Voice POWER Fig.6: the front panel label we used for the Galactic Voice. A colour copy or printout can be glued to the disk. siliconchip.com.au Capacitor Codes Value (mF value)   IEC    EIA     Code  Code 220nF 0.22mF 220n 224 100nF 0.1mF 100n 104 47nF .047 47n 473 33pF NA 33p 33 audible feedback commences. Try speaking into the microphone and adjust the effects and depth pots to see if they are working. If the LED doesn’t light or if you aren’t getting any output, first check the polarity of the wiring. You should also check the parts on the PC board for correct placement and correct orientation for the polarised parts. Having said that, kit suppliers tell us that 99% of faults in projects are due to soldering problems – particularly dry joints – so if you aren’t having any joy, check your soldering again! Check that power is available between pins 4 and 8 of IC1, pins 1 and 4 of IC2 and pins 4 and 6 of IC4. A fresh battery should give 8.7V across each of these sets of pins. The Null control is adjusted when VR1 is wound to its maximum (fully clockwise) and the volume turned up but not too high that there is feedback. Adjust VR4 so that no tone can be heard when there is no noise present at the microphone. Finally, when it all works correctly, the assembly can be slid into the rear of the tube. Note that the speaker wire needs to be kept tight when sliding in so it does not become caught between the rear of the speaker and the support PC board. The wire is tucked in behind the volume potentiometer. Secure the assembly by screwing the M4 screw into the support PC board’s M4 nut after you have lined the two up. nuqneH! (and if you don’t understand what that means, you really need to brush up on your Klingon – otherwise you might make a mistake SC and be exterminated!) GALACTIC VOICE JC Insert the 9V battery and check that the Galactic Voice works by switching on power. The power LED should light and a squeal should come from the loudspeaker if the volume is wound up. Needless to say, that’s feedback caused by the microphone and speaker being in close proximity. But that feedback can also be used to give even more variety to the sound output, especially if adjusted until just before 5-Band Code (1%) yellow violet black orange brown red red black orange brown brown black black orange brown orange white black red brown brown black black red brown orange orange black brown brown red red black brown brown brown black black brown brown brown black black gold brown 08109061 Wire the speaker wires to the PC stakes and the battery holder wires to the PC board taking care to make the correct polarity for the connection. Solder the support PC board at right angles to the main PC board – it solders to the four PC stakes located at the end of the PC board. A 4mm hole is required to be drilled on the side of the speaker port tube at the flared end 95mm from the nonflared end. This is for the M4 screw to be screwed into the M4 nut on the support PC board. 4-Band Code (1%) yellow violet yellow brown red red yellow brown brown black yellow brown orange white orange brown brown black orange brown orange orange red brown red red red brown brown black red brown brown black black brown 08109062 GALACTIC VOICE Fig.7: 1:1 artwork for both of the PC boards with the support PC board at bottom. Note the cutouts needed in this board. September 2006  73