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Disguise your voice to sound like Darth Vader from “Star Wars” or a Cylon from “Star Trek”. With the added menace of a new strange-sounding voice, you too can travel the galaxy for profit and entertainment. By JOHN CLARKE e c i o V r e d Va T HE DARTH VADER and Cylon characters have always had great appeal, probably because of their distinctive metallic voice styles. This simple project lets you imitate the dastardly Darth and other diabolical characters from the nether regions of the galaxy. All you do is switch it on, speak into a small electret microphone and adjust a single pot to get the effect you want. Now it’s quite possible that some people might not see the need for building such a handy space-war accessory as this. To others, the reasons will be self-evident – after all, why should you be forced to stick with your own everyday boring voice? As can be seen from the photos, 22  Silicon Chip the Vader Voice is housed in a small plastic case. The controls include an effects rate ad­justment (which varies the type of sound), a volume control to set the output level from the loudspeaker and an on/off switch. The loudspeaker is mounted inside the case while the microphone is located in a small film canister connected via a length of shielded cable. How it works Fig.1 shows the block diagram for the Vader Voice. The action starts on the lefthand side, where an electret microphone feeds signal to an op amp stage (IC1a) which has a gain of about 15. A chopper circuit (ie, CMOS switch IC2) then switches the signal on and off at a rate determined by oscillator stage IC3 and potentiometer VR1. The output from the chopper stage is fed to a 3kHz low-pass filter based on IC1b. This stage removes the residual signals produced by the switching action in IC2. Finally, IC4 feeds the processed signal to power amplifier stage IC4 via volume control VR2. Fig.2 illustrates how the circuit produces the sound ef­ fects. Waveform A is the audio signal from the microphone after passing through amplifier IC1a, while waveform B is the square wave output from the oscillator. Waveform C shows the audio signal after it has been “chopped” at the oscillator frequency. The bottom waveform at D shows the corresponding output from the low-pass filter (IC1b). Note that this waveform is quite different in appearance to the original waveform shown at A and it sounds correspondingly different too. Refer now to Fig.3 for the complete circuit. Apart from the microphone and loudspeaker, it uses four lowcost ICs plus a few resistors and capacitors. The electret microphone requires a bias in order to func­tion. This is supplied via a 10kΩ resistor which is decoupled from the supply rail via a 1kΩ resistor and 33µF capacitor. This decoupling arrangement is necessary to prevent supply line fluc­ tuations caused by the power amplifier stage from modulating the microphone and causing positive feedback. The signal from the electret microphone is fed via a .0033µF capacitor to pin 3 of op amp IC1a. This stage is con­nected as a non-inverting amplifier with a gain of about 15, as set by the 470kΩ feedback resistor and the 33kΩ resistor on pin 2 (ie, Gain = 1 + 470/33 = 15.2). IC1a is biased at half the supply voltage via two 220kΩ resistors and the associated 470kΩ resistor connected to pin 10. A 10µF electrolytic capacitor decouples the half-supply voltage, which is also used to bias pins 2 & 1 of IC2 and pin 5 of op amp IC1b. As a result of this bias arrangement, the output from IC1a swings above and below +4.5V. AMPLIFIER x15.5 MICROPHONE IC1a 3kHz LOW PASS FILTER IC1b CHOPPER IC2 A C POWER AMPLIFIER D VOLUME VR2 IC4 B EFFECT RATE VR1 LOUDSPEAKER OSCILLATOR IC3 Fig.1 (above): block diagram of the Vader Voice. The signal from the microphone is amplified in IC1a and “chopped” in IC2 at a rate set by oscillator IC3. The resulting signal is ten filtered in IC1b and fed to audio amplifier stage IC4. A B Fig.2 (right): this diagram shows the effect on the input waveform at various points in the circuit. Note that the output waveform (D) is quite different to the input waveform (A). The oscillator stage is formed by IC3 which is a 7555 CMOS timer. This stage generates a square wave output with a frequency in the range from 1.3kHz to 14kHz, depending on the setting of VR1. Let’s see how it works. At switch on, the 0.1µF timing capacitor is initially dis­ c harged and the output at pin 3 is high. The 0.1µF capacitor then charges via the 1kΩ resistor and VR1 until it reaches 2/ Vcc (ie, 2/ the supply voltage). 3 3 When it does, pin 3 switches low C D and the timing capacitor discharges via the 1kΩ resistor and VR1 until it reaches 1/3Vcc. This switches pin 3 high again and so the process is repeated indefinitely while ever power is applied. Fig.3 (below): the final circuit uses 7555 timer IC3 to drive CMOS switch IC2 and this stage in turn chops the audio waveform from IC1a. IC1b is the 3kHz low-pass filter stage and this drives IC4 via volume control VR2. S1 1k 33 10k 0.1 220k .0033 470k MIC 220k 8 3 10 16VW 33k 2 IC1a LM358 9V IC2 4066 1 .0068 14 2 13 470k 470k 1 7 10k .012 22k 10k .01 .001 10k 6 5 4 470k 7 IC1b VOLUME VR2 10k LOG RATE VR1 10k LIN +9V 4 1k 6 8 3 6 5 IC4 2 LM386 4 .047 100 16VW 8W 10  0.1 3 IC3 7555 2 100 16VW 0.18 1 VADER VOICE 0.1 September 1995  23 1 100uF 33k 470k 220k 220k IC2 4066 .01 .012 C ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ 9V BATTERY AND CLIP 1 .0033 .047 TABLE 2: CAPACITOR CODES 10uF IC1 LM358 0.1 IC3 7555 0.1 0.1 1 D .0068 470k A 470k B 1k 100uF S1 10k IEC Code 180n 100n 47n 12n 10n 6n8 3n3 1n0 EIA Code 184 104 473 123 103 682 332 102 10k 0.18 1 1k 22k 10k 470k 10  IC4 LM386 10k Value 0.18µF 0.1µF .047µF .012µF .01µF .0068µF .0033µF .001µF .001 33uF C the output each time the potentiometer was operated. Following VR2, the signal is coupled to pin 3 of IC4, an LM386 audio amplifier which is capable of driving an 8Ω loud­speaker at an output power of up to 1W. Its output appears at pin 5 and drives the loudspeaker via a 100µF capacitor which rolls off the response below about 200Hz. In addition, a Zobel network consisting of a .047µF capacitor and a 10Ω resistor is connected across the output of IC4 to prevent high frequency instability. Power for the circuit comes from a 9V battery and is ap­plied via on/off switch S1. A 100µF electrolytic capac­ itor provides supply line de­coup­ling, to minimise variations due to the peak currents through the LM386 audio amplifier. D VR2 A B SPEAKER VR1 MICROPHONE Fig.4: install the parts on the PC board and complete the wiring as shown in this diagram. Note that shielded cable is used for the connections to volume control VR2 and to the electret microphone. The square wave output at pin 3 of IC3 toggles CMOS analog switch IC2 on and off. When pin 3 of IC3 is high, the CMOS switch is closed. Conversely, when pin 3 is low, the CMOS switch is open. As a result, the signal from IC1a is gated at the oscilla­tor frequency before it is fed to IC1b. IC1b and its associated resistors and capacitors form the third order Construction low-pass filter. This rolls off the signal above 3kHz at 60dB per decade (ie, 20dB/octave). This means that at 30kHz the signal is attenuated by 60dB. The filtered signal appears at pin 7 of IC1b and is AC-coupled via a 0.18µF capacitor to volume control VR2. This AC coupling prevents DC from flowing in VR2, which would cause noise in A PC board coded 08310951 carries most of the parts for the prototype. This board was housed in a plastic case measuring 130 x 67 x 43mm, while a self-adhesive label was designed for the front panel. Fig.4 shows the wiring details. Start the PC board assembly by installing PC stakes at all external wiring points and at the S1 position. This done, install TABLE 1: RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 4 2 1 1 4 2 1 24  Silicon Chip Value 470kΩ 220kΩ 33kΩ 22kΩ 10kΩ 1kΩ 10Ω 4-Band Code (1%) yellow violet yellow brown red red yellow brown orange orange orange brown red red orange brown brown black orange brown brown black red brown brown black black brown 5-Band Code (1%) yellow violet black orange brown red red black orange brown orange orange black red brown red red black red brown brown black black red brown brown black black brown brown brown black black gold brown PARTS LIST 1 PC board, code 08310951, 82 x 62mm 1 plastic case, 130 x 67 x 43mm 1 front panel label, 62 x 212mm 2 knobs 1 SPDT toggle switch (S1) 1 57mm diameter 8-ohm loudspeaker 1 9V battery clip 1 9V battery 12 PC stakes 1 electret microphone insert 1 16mm 10kΩ linear pot (VR1) 1 16mm 10kΩ log pot (VR2) 1 800mm-length of shielded cable 1 80mm-length of twin speaker wire 1 200mm-length of hookup wire 1 20mm-length of 0.8mm tinned copper wire Semiconductors 1 LM358N dual op amp (IC1) 1 4066B quad analog switch (IC2) 1 7555 CMOS timer (IC3) 1 LM386N audio amplifier (IC4) The PC board was secured by clipping it into slots that run along either side of the case, while the loudspeaker was fastened to the lid using contact adhesive. Make sure that the battery clip is correctly wired to the board. the wire link adjacent to IC2, then install the resistors and capacitors. Tables 1 & 2 show the resistor and capacitors codes but it is also a good idea to check the resistor values using a multimeter, as some colours can be difficult to read. Take care to ensure that the four electrolytic capacitors are correctly oriented. In particular, note that the two 100µF capacitors are oriented in opposite directions. The three ICs can now be installed, again taking care to ensure that they are all correctly oriented. It is quite easy to identify pin 1 of an IC, as it is always adjacent to a dot or notch in one end of the IC’s body (see Fig.4). Be careful not to get the 8-pin ICs mixed up and don’t use a conventional 555 timer for IC3. It must be a CMOS 7555 type to ensure low battery drain. Switch S1 is mounted on top of the PC stakes, to give it sufficient height to later protrude through the front panel. When the PC board has been completed, it can be clipped into the case as shown in the photo. Next, affix the adhesive label to the lid of the case and use it as a template for drilling the holes. You will have to drill holes for the Volume and Effect pots, the Power switch and the loudspeaker grille. A small hole is also required in one end of the case for the microphone lead. Take care when mounting the two pots on the lid. VR1 (Ef­fects) is a 10kΩ linear type, while VR2 (Volume) is a 10kΩ log type. The loudspeaker is mount­ed using contact adhesive. Once everything is in position, the wiring can be completed as shown in Fig.4. Light-duty figure-8 cable is used Capacitors 2 100µF 16VW PC electrolytic 1 33µF 16VW PC electrolytic 1 10µF 16VW PC electrolytic 1 0.18µF MKT polyester 3 0.1µF MKT polyester 1 .047µF MKT polyester 1 .012µF MKT polyester 1 .01µF MKT polyester 1 .0068µF MKT polyester 1 .0033µF MKT polyester 1 .001µF MKT polyester Resistors (0.25W, 1%) 4 470kΩ 4 10kΩ 2 220kΩ 2 1kΩ 1 33kΩ 1 10Ω 1 22kΩ Miscellaneous Plastic 35mm film canister, epoxy resin, solder for the loudspeaker connections and for wiring the Effects pot, while shielded cable must be used for the Volume control wiring. The battery clip can also be wired in at this stage –be sure to connect the red lead to the positive terminal on the PC board. Shielded cable must also be used September 1995  25 Fig.5: this is the full-size etching pattern for the PC board. Check your board carefully before installing any parts. for the microphone lead. Use a length of about 600mm and feed it through the end of the case before soldering it to the PC board terminals. The micro­phone itself can be mounted in a plastic film canister or some other similar plastic container. In the prototype, the microphone was mounted through a hole drilled in the cap of the film canister and secured with a dab of epoxy. The lead passes through a second hole drilled in the bottom of the canister. Finally, the battery can be clipped into position and the lid attached. Testing To test the project, simply switch it on, wind the volume control up and speak into the microphone. You should immediately be rewarded with a metallic sounding voice. Adjust the Effects pot (VR1) until you obtain the sound you want. All you need now is a helmet, a black cloak, a breathing mask and a light stick to terrorise the galaxy, or just the immediate neighbourhood. If Darth doesn’t do his stuff, first check that each com­ ponent is in its correct location and that all polarised parts are correctly oriented. You should also carefully check the underside of the PC board for solder bridges or missed (or bad) solder connections. Next, check for +9V on pin 8 of IC1, pin 14 of IC2, pins 4 & 8 of IC3 and pin 6 of IC4. Pins 2 & 5 of IC1 should be at +4.5V, as should pins 1 & 2 of IC2. Check the relevant circuit components carefully if you do encounter any incorrect voltages. If all you get is your normal amplified voice, check that oscillator IC3 is working correctly. It should have an average voltage of 4.5V at pin 3, as measured on a multimeter. If you don’t get any sound at all, try bridging pins 2 & 1 on IC2. This will tell you whether or not CMOS switch IC2 is functioning, or whether the fault lies elsewhere in the circuit. SC ANOTHER GREAT DEAL FROM MACSERVICE 100MHz Tektronix 465M Oscilloscope 2-Channel, Delayed Timebase VERTICAL SYSTEM Bandwidth & Rise Time: DC to 100MHz (-3dB) and 3.5ns or less for DC coupling and -15°C to +55°C. Bandwidth Limit Mode: Bandwidth limited to 20MHz. Deflection Factor: 5mV/div to 5V/div in 10 steps (1-2-5 sequence). DC accuracy: ±2% 0-40°C; ±3% -15-0°C, 40-55°C. Uncalibrated, continuously variable between settings, and to at least 12.5V/div. Common-Mode Rejection Ratio: 25:1 to 10MHz; 10:1 from 10-50MHz, 6cm sinewave. (ADD Mode with Ch 2 inverted.) Display Modes: Ch 1, Ch 2 (normal or inverted), alternate, chopped (250kHz rate), added, X-Y. Input R and C: 1MΩ ±2%; approx 20pF. Max Input Voltage: DC or AC coupled ±250VDC + peak AC at 50kHz, derated above 50KHz. HORIZONTAL DEFLECTION Timebase A: 0.5s/div to 0.05µs/div in 22 steps (1-2-5 sequence). X10 mag extends fastest sweep rate to 5ns/div. Timebase B: 50ms/div to 0.05µs/div in 19 steps (1-2-5 sequence). X10 mag extends maximum sweep rate to 5ns/div. Horizontal Display Modes: A, A Intensified by B, B delayed by A, and mixed. CALIBRATED SWEEP DELAY Calibrated Delay Time: Continuous from 0.1µs to at least 5s after the start of the delaying A sweep. Differential Time Measurement Accuracy: for measurements of two or more major dial divisions: +15°C to +35°C 1% + 0.1% of full scale; 0°C to +55°C additional 1% allowed. TRIGGERING A & B A Trigger Modes: Normal Sweep is triggered by an internal vertical amplifier signal, external signal, or internal power line signal. A bright baseline is provided only in presence of trigger signal. Automatic: a bright baseline is displayed in the absence of input signals. Triggering is the same as normal-mode above 40Hz. Single (main time base only). The sweep occurs once with the same triggering as normal. The capability to re-arm the sweep and illuminate the reset lamp is provided. The sweep activates when the next trigger is applied for rearming. A Trigger Holdoff: Increases A sweep holdoff time to at least 10X the TIME/DIV settings, except at 0.2s and 0.5s. Trigger View: View external and internal trigger signals; Ext X1, 100mV/div, Ext -: 10, 1V/div. Level and Slope: Internal, permits triggering at any point on the positive or negative slopes of the displayed waveform. External, permits continuously variable triggering on any level between +1.0V and -1.0V on either slope of the trigger signal. A Sources: Ch 1, Ch 2, NORM (all display modes triggered by the combined waveforms from Ch 1 and 2), LINE, EXT, EXT :-10. B Sources: B starts after delay time; Ch 1, Ch 2, NORM, EXT, EXT :-10. Optional cover for CRT screen – $35 through the vertical system. Continuously variable between steps and to at least 12.5V/div. X Axis Bandwidth: DC to at least 4MHz; Y Axis Bandwidth: DC to 100MHz; X-Y Phase: Less than 3° from DC to 50kHz. DISPLAY CRT: 5-inch, rectangular tube; 8 x 10cm display; P31 phosphor. Graticule: Internal, non-parallax; illuminated. 8 x 10cm markings with horizontal and vertical centerlines further marked in 0.2cm increments. 10% and 90% for rise time measurements. Australia’s Largest Remarketer of markings Graticule Illumination: variable. Beam Test & Measurement Equipment Finder: Limits the display to within the graticule area and provides a visible 9500; Fax: (03) 9562 9590 display when pushed. X-Y OPERATION Sensitivity: 5mV/div to 5V/div in 10 steps (1-2-5 sequence) MACSERVICE PTY LTD 20 Fulton Street, Oakleigh Sth, Vic., 3167. Tel: (03) 9562 **Illustrations are representative only. Products listed are refurbished unless otherwise stated. 26  Silicon Chip $900