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Control barking dogs with the Woofer Stopper Mk.2 This completely new version of the Woofer Stopper has much higher power, with pulsed and variable output frequency between 20kHz and 25kHz. It automatically senses the barking of a dog using an inbuilt electret microphone. By JOHN CLARKE 36  Silicon Chip Now it’s your turn to get back at your neighbour’s barking dog without anyone knowing about it. The Woofer Stopper will give a blast of high intensity sound every time the dog barks. When subjected to this treatment, most dogs quickly learn that barking means punishment and they stop. Don’t get us wrong. The Woofer Stopper Mk.2 will not stop all dogs from barking. Some dogs are deaf or are completely stupid and would continue to bark under any circumstances. Provided they are not too far away from the Woofer Stopper though, say 30 metres or less, most dogs will be deterred from barking. Our first Woofer Stopper, published in the May 1993 issue, created a huge amount of interest. Obviously, barking dogs are a source of much annoyance to many people. While the Woofer Stopper was successful in many cases, we have had readers calling for more power and for automatic sensing of the dog barking. The result is the Woofer Stopper Mk.2. This version has a far greater voltage output and can drive a maximum of four pie­zo­ Fig.1: this is the block diagram of the Woofer Stopper Mk.2. An electret microphone electric tweeters. These can be in is used to pick up the sound of a dog barking, to provide an automatic trigger for the form of four single devices or the circuit. The output stage can drive up to four piezo tweeters. two duals. To obtain the maximum possible sound output, we have re­sorted to two types of tweeter. The first is the 1177A TD Twin Tweeter. It produces Motorola KSN 1005A Super Horn. 99dB SPL at 1-metre and 2.82V RMS a number of measures. First, instead It can produce a 94dB SPL (sound drive and is rated at 28V maximum. of driving the tweeter with a constant Note that the second type is a dual high frequency of around 20kHz, pressure level) at 1-metre with 2.82V we frequency modulate the signal RMS drive. They are rated at 15V RMS tweeter and this accounts for the 5dB continuous and 24V RMS maximum. increase in SPL. Other types can be between 20kHz and 25kHz. This has The second type is the Motorola KSN used, although we do not know how been done to overcome the inevitable peaks and dips in the response of piezo tweeters. By modulating the output frequency over a 5kHz range, we obtain a high effective output. Second, instead of driving the tweeters at a constant vol­ tage, we pulse them at a voltage much higher than their continu­ous rating – again to produce a higher output level. And third, instead of driving them with a square wave signal, we drive them with a sinewave. While developing the Woofer Stopper Mk.2, we found that driving piezo tweeters with high-voltage square These are the two piezo tweeters waves caused them to fail. This is recommended for use with because they are essentially a capacthe Woofer Stopper Mk.2. The Motorola KSN 1177A TD Twin itor, with a capacitance ranging from Tweeter is at left while the KSN .01µF to 0.3µF, depending on the mod1005A Super Horn is shown el. Driving such a capacitance with above. high-voltage square waves at around 20kHz or more causes very high peak currents and this caused the internal SPECIFICATIONS connecting wires to fuse. Since we wanted a lot more power than proSupply Voltage: 12VDC duced by the previous design, we Output Voltage (two transducers driven; deduct 20% for four devices): could not use square waves; sinewave    (a) 21.4VRMS peak and 14.2VRMS continuous with 13.8V supply drive was the way to go.    (b) 18.5VRMS peak and 12.4VRMS continuous with 12V supply Recommended tweeters Peak burst duration: 100ms every 1 second Since the Mk.2 version produces a lot more output than the original version, it makes sense to team it with highly efficient piezo tweeters which can handle the high power levels involved. Using cheap tweeters will be a waste of money. We recommend Total output duration: 5,10,20,40 & 160 seconds Standby current: 30mA Current while driving transducers: 1A average Output frequency: shifted continuously between 20kHz and 25kHz every 220ms February 1996  37 Fig.2: the full circuit diagram of the Woofer Stopper Mk.2. Note the audio amplifier involving IC6 and tran­sistors Q1 & Q2. These provide increased power and can drive up to four piezo tweeters via step up transformer T1. they will respond to the high voltage drive. Bark sensing & timer The Woofer Stopper Mk.2 has an inbuilt electret microphone to sense 38  Silicon Chip the sound of a dog barking and start the unit operating. While this is adjustable in sensitivity, it is quite likely that it will be triggered by other loud sounds and this could ul­timately be counterproductive. We see the pur- pose of the Woofer Stopper Mk.2 as a teaching aid – to stop a dog from barking. If it is triggered by other noises, it may not be as effective. However, we have included this feature because it has been re­quested frequently by readers. The unit can also be triggered into operation by pushing a button and in either case, the tweeter will sound for a preset period which can be programmed, from five seconds to 160 seconds. The idea of having the timer is to avoid the possibility of the unit being turned on for long periods which would waste power and possibly reduce its effectiveness in teaching the dog not to bark. The Woofer Stopper can be run from a 12V battery or a DC power supply capable of delivering one amp or more. Block diagram Fig.1 shows the block diagram of the Woofer Stopper Mk.2. It shows an electret microphone fed to IC1a & ICb, comparator IC2 and flipflop IC3 which controls the counter IC4. IC5 and IC2c comprise the 20kHz oscillator which is fre­quency modulated by IC2b. Finally, there is the power amplifier comprising IC6, Q1 and Q2, which drives a step-up transformer T1. The gain of the power amplifier is periodically increased by the burst oscillator IC2d and Q3. Counter IC4 resets the flipflop after a preset time and the 20kHz oscillator is reset. Thus, sound from the transducer is stopped until retriggered by the microphone. Note that because the microphone will also respond to the transducer sound, the reset time for the flipflop is made long enough to prevent re­triggering at the end of the time period. Circuit details The complete circuit for the Woofer Stopper Mk.2 is shown in Fig.2. The electret microphone is biased by a 4.7kΩ resistor and its signal is coupled to op amp IC1 via a .022µF capacitor. IC1a is a non-inverting amplifier with its low frequency response curtailed below 1600Hz, by virtue of the 10kΩ resistor and .01µF capacitor at pin 6. Its gain is set by trimpot VR1. IC1a’s output is coupled to a virtually identical stage, apart from the sen­sitivity control, comprising op amp IC1b. Its gain is 19 and is also rolled off above 5kHz by the 150pF capacitor shunting the 180kΩ feedback resistor. IC2a squares up the output signal of IC1b. IC2a is connect­ed as a Schmitt trigger with positive feedback between the non-inverting input at pin 3 and its output at pin 1. When flipflop IC3 is triggered by a high-going pulse from IC2a, its Q output goes high which allows IC5, a 7555 timer, to begin os- PARTS LIST 1 plastic case, 198 x 113 x 63mm 1 PC board, code 03102961, 153 x 103mm 1 self-adhesive label, 107 x 193mm 1, 2, 3 or 4 KSN 1005 Motorola superhorn loudspeakers (DSE Cat C-2205) or 1 or 2 KSN 1177 Motorola twin tweeters (DSE Cat C-2204) 1 red binding post 1 black binding post 1 2.5mm DC panel socket 1 2.5mm DC panel plug 1 SPDT toggle switch (S1) 1 momentary pushbutton switch (S2) 1 electret microphone insert 1 ETD29 3C85 or 3F3 transformer cores, bobbin and clips (Philips 2 x 4312 020 37502 , 1 x 4322 021 34381 , 2 x 4322 021 34371) (T1) 2 mini heatsinks, 25 x 30 x 13mm 1 4.5m length of 0.5mm diameter enamelled copper wire 1 140mm length of black hook-up wire 1 200mm length of red hook-up wire 1 200mm length of 0.8mm tinned copper wire 8 PC stakes 2 3mm screws and nuts 2 5mm LED bezels 1 200kΩ horizontal trimpot (VR1) 1 20kΩ horizontal trimpot (VR2) Semiconductors 1 LF353, TL072 dual op amp (IC1) 1 LM324 quad op amp (IC2) cillating. At the same time, the Q-bar output of IC3 goes low to release the reset on counter IC4 which begins to count the clock pulses from oscillator IC2b. IC4 counts for a period selected by installing the appro­priate link (LK1LK5). When the selected Q output goes high, the 33µF capacitor at pin 4 of IC3 is charged via D2 to reset the flipflop. The Q output of IC3 now goes low to stop IC5 from oscillating and the Q-bar output goes high to reset counter IC4. Now the selected Q 1 4013 dual D flipflop (IC3) 1 4020 binary counter (IC4) 1 7555, LMC555CN, GLC555 CMOS timer (IC5) 1 NE5534N op amp (IC6) 1 MJE3055 TO220 NPN transistor (Q1) 1 MJE2955 TO220 PNP transistor (Q2) 1 BC338 NPN transistor (Q3) 1 1N4004 1A rectifier diode (D1) 2 1N914, 1N4148 switching diodes (D2,D3) 1 5mm red LED (LED1) 1 5mm green LED (LED2) Capacitors 2 470µF 16VW PC electrolytic 1 47µF 16VW PC electrolytic 1 33µF 16VW PC electrolytic 2 10µF 16VW PC electrolytic 1 2.2µF 16VW PC electrolytic 1 0.1µF MKT polyester 2 .022µF MKT polyester 3 .01µF MKT polyester 1 .0022µF MKT polyester 1 150pF ceramic 1 120pF ceramic 1 82pF ceramic 1 39pF ceramic Resistors (0.25W, 1%) 1 1MΩ 15 10kΩ 1 560kΩ 2 6.8kΩ 1 180kΩ 2 4.7kΩ 5 100kΩ 2 2.2kΩ 1 68kΩ 1 560Ω 1 47kΩ 1 100Ω 1 15kΩ Miscellaneous Solder, insulating tape. output on IC4 goes low and the 33µF capacitor at pin 4 of IC3 discharges (or actually charges) via the 100kΩ resistor to ground. This means that IC3 is again ready to respond to the signal from IC2a and recommence the sequence. 20kHz oscillator The main oscillator is based on IC5, a CMOS 7555 timer which is connect­ ed in an unconventional way. It successively charges and discharges the .0022µF capacitor at pin 2 & 6 via the February 1996  39 Fig.3: install the parts on the PC board and complete the wiring as shown here. In particular, take care to ensure that all polarised parts are correctly oriented and note that the metal tabs of audio output transistors Q1 and Q2 are bolted to small U-shaped heatsinks and to the PC board. 15kΩ resistor from pin 3. Instead of using the square wave output signal at pin 3, we take the triangle waveform at pin 6. This triangle waveform is buffered by unity gain op amp IC2c and then fed to a low-pass filter comprising a 100kΩ resistor and 120pF capacitor. This network effectively 40  Silicon Chip removes the higher harmonics and the result is a clean sinewave at around 20kHz. However, the timer/oscillator IC5 is also frequency modu­lated by the triangle signal applied to pin 5 from pin 6 of IC2b, a low frequency oscillator. Op amp IC2b is connected as a Schmitt trigger oscillator. It charges and discharges the 2.2µF capacitor at pin 6 via the 100kΩ resistor from pin 7. The result is a square wave at about 2.5Hz at pin 7 and a triangle waveform of the same frequency at pin 6 (ie, across the 2.2µF capacitor). As noted above, the square wave pulses from CAPACITOR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Value 0.1µF .022µF .01µF .0022µF 180pF 120pF 82pF 39pF IEC 100n 22n 10n 2n2 180p 120p 82p 39p EIA 104 223 103 222 181 121 82 39 IC2b are used to clock counter IC4 while the triangle pulses frequency modulate IC5. IC6 amplifies the frequency-modulated sinewave from IC2c. Its current drive capability is boosted by common emitter output transistors Q1 & Q2. The 560Ω resistor between the base and emitter connections provides a current path for the output of the amplifier whenever Q1 or Q2 is biassed off and helps prevent instability. The 39pF compensation capacitor between pins 5 & 8 and the 82pF feedback capacitor roll off the amplifier gain above about 40kHz. Gain boosting The gain of IC6 is pulsed up and down by the waveform from oscillator IC2d which switches transistor Q3 on and off. With Q3 off, the gain is about 1.5, set mainly by the 68kΩ resistor across Q3. When Q3 is on, the gain can be set between 11 and 2.9 The electret microphone insert is a flush fit in one end of the case, as shown here. Connect the microphone so that its positive terminal goes to the 4.7kΩ resistor. The terminal that’s connected to the case goes to ground. by adjusting trimpot VR2. Thus, the gain varies between about 1.5 and a figure set by VR2 at a rate controlled by IC2d. IC2d operates in a similar manner to oscillator IC2b. The 10µF capacitor at pin 13 is charged via the 10kΩ resistor and diode D3 when pin 14 is high and discharges via the 100kΩ resis­tor when pin 14 is low. Thus, the output is high for only a short time. The duty cycle of the pulse waveform is about 1:10. Transformer T1 steps up the voltage from the output amplifi­er by a factor of 10. Thus, the output across the piezo tweeters can be as much as 75V peakpeak. In practice, the actual setting will depend on the tweeters used. Above a certain voltage level, the tweeter will overload and will protest audibly. It would not be wise to run tweeters under this overload condition for long as you risk burning them out. Power supply Power for the circuit is derived from a 12V battery or DC power supply capable of supplying at least 1A. Diode D1 provides polarity reversal RESISTOR COLOUR CODES ❏ No. ❏   1 ❏   1 ❏   1 ❏   5 ❏   1 ❏   1 ❏   1 ❏ 15 ❏   2 ❏   2 ❏   2 ❏   1 ❏   1 Value 1MΩ 560kΩ 180kΩ 100kΩ 68kΩ 47kΩ 15kΩ 10kΩ 6.8kΩ 4.7kΩ 2.2kΩ 560Ω 100Ω 4-Band Code (1%) brown black green brown green blue yellow brown brown grey yellow brown brown black yellow brown blue grey orange brown yellow violet orange brown brown green orange brown brown black orange brown blue grey red brown yellow violet red brown red red red brown green blue brown brown brown black brown brown 5-Band Code (1%) brown black black yellow brown green blue black orange brown brown grey black orange brown brown black black orange brown blue grey black red brown yellow violet black red brown brown green black red brown brown black black red brown blue grey black brown brown yellow violet black brown brown red red black brown brown green blue black black brown brown black black black brown February 1996  41 These two oscilloscope photos show the output waveform of the Woofer Stopper. The photo at left shows the frequency modulation while the shot at right shows the pulsed wave­form. protection while the associated 470µF capacitor decouples the supply for the high current pulses drawn by the amplifier. Construction Fig.4: the full-size etching pattern for the PC board. Check the board carefully for defects before installing any of the parts. 42  Silicon Chip The Woofer Stopper is housed in a plastic case measuring 198 x 113 x 63mm and the components are mount­ ed on a PC board coded 03102961 and measuring 153 x 103mm. The component layout for the PC board is shown in Fig.3. Start construction by checking the PC board against the published pattern. Repair any shorts or breaks in the tracks before assembly of the components. There should be 3mm holes drilled for mounting Q1 and Q2 on their heatsinks. First, install the eight PC stakes and the bare wire links. Insert LK2 at this stage. This gives a 10-second period of operation and you can change this later to the desired setting. Next, the resistors can be inserted and soldered, using the accom­panying resistor code table as a guide when selecting each value. If in doubt, use your multimeter to check the resistance values. Next, insert the ICs, making sure that each one is in its correct place and oriented correctly, then do the capacitors. Note that the electrolytic capacitors must be oriented as shown in Fig.3 for correct polarity. Mount trimpots VR1 & VR2 and transistor Q3. Transistors Q1 and Q2 are mount­ed horizontally on small heat­sinks. Bend their leads so that they will fit neatly into the PC board and secure the transistor tab to the heatsink with a 3mm screw and 0N + + START + + TRIGGERED WOOFER STOPPER MKII SPEAKER TERMINALS nut before soldering the leads to the PC board. Winding the transformer is straightforward. The winding details are shown in Fig.6. Terminate one end of the 0.5mm enam­elled copper wire to pin 9 of the bobbin. To do this, you will need to strip the end of the wire of insulation and then tin it with solder. Wind on eight turns and terminate the end of the winding to pin 11 of the bobbin. Apply a layer of insulating tape over this winding. The secondary winding is done in a similar manner by starting at pin 2 and winding on 80 turns in several layers. Insulate each layer with tape and finally terminate onto pin 5. The transformer is then assembled by sliding the cores into each end of the bobbin and securing them with the clips. Mount the transformer onto the board and solder the pins in place. Work can now begin on the case. Attach the adhesive label to the case lid and drill the switch, LED bezel and corner mount­ing holes. Drill holes in one end of the box for the DC socket and electret microphone and at the opposite end for the tweeter terminals. Make sure that the electret microphone is a tight fit in its mounting hole. If necessary, secure it with a drop of 5-minute epoxy adhesive. Clip the PC board into the base of the case. The tweeter terminal eyelet connections can be soldered directly to the PC stakes or you can use short lengths of tinned copper wire. Testing When wiring is complete, you should check your work care­fully for errors. Once you are satisfied that all is correct, you are ready to connect up power. The Woofer Stopper will operate from a 12V gel cell battery rated at 1.2Ah or higher. It can also be run from a DC power supply capable of at least 1A at 12V. Apply power and check voltages on the circuit. There should be +12V at pin 8 of IC1, pin 4 of IC2, pin 14 of IC3, pin 16 of IC4, pins 8 of IC5 and pin 7 of IC6. Check that the power LED lights. Connect your multimeter across the output terminals and set it to read 20VAC. Wind trimpot VR1 fully clockwise for maximum microphone sensitivity and check that there is an output signal on the meter when triggered by tapping the microphone. POWER IN (12VDC + ) Fig.5: this full size artwork can be photocopied and used as a drilling template for the front panel. You will find that the microphone sensitivity is very high at this set­ting. Reduce VR1 to a setting which will only retrigger the circuit with a reasonable amount of noise. Trying barking yourself if the mood takes you. Test the manual trigger switch as well. Note that LED2 should light whenever the circuit is triggered. Note that the reading on the meter will not necessarily be the true output level. This is because some multi­ meters do not respond well at 20kHz. Connect up your piezo tweeters and again apply power. The level of VR2 should be adjusted so that you do not hear the sound output during the bursts. Unless you can actually February 1996  43 Fig.5: follow this winding diagram when making the step-up transformer (T1). The primary is wound on first and is covered with a layer of insulating tape. The secondary is then wound over the top of the primary. hear 20kHz, any audible sounds from the tweeters is distortion and is quite small relative to the fundamental output at 20kHz. If you want to check that the circuit is working you can lower the frequen- Transistors Q1 and Q2 are mounted horizontally on small heat­ sinks. Bend their leads so that they fit neatly into the PC board and secure their tabs to the heatsinks and the PC board using machine screws and nuts. cy of oscillation by adding a second .0022µF capacitor between pins 2 and 1 of IC5. This will halve the output frequency to 10kHz. Be warned that the output is extremely loud and will damage your ears if you do not use ear plugs. You can also use a 1kΩ resistor or high value resistor in series with the tweeter to reduce the output level. Return the circuit to 20kHz operation by removing the ca­pacitor and you are ready to test it on an unsuspecting dog. As mentioned, you can use up to four piezo tweeters in parallel (two KSN 1177A or four KSN 1005A tweeters). These can be mounted on a board and oriented either horizontally or vertical­ly, depending on the sound pattern you require. Do not use con­ventional tweeters (ie, those with voice coils). The circuit cannot handle them. Note that you can omit the electret microphone if you wish and just use manual triggering. Alternatively, you could add in a switch to turn off the microphone when you want to use manual triggering only. You could also incorporate UHF remote triggering, as was used for the original version of the Woofer Stopper. The details were published in the June SC 1993 issue of SILICON CHIP. Warning! This internal view of the Woofer Stopper shows how the board fits neatly in the case. The step up transformer and opera­tion with sinewave drive are the main factors in the increased output. 44  Silicon Chip The output from this Woofer Stopper is at a very high level. Even though you cannot hear the noise, take care to keep away from the front of the tweeters when they are being driven. They may cause ear damage.