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Raucous Alarm . . . the alarm that everyone will hate hearing Make no mistake: this alarm sounds quite horrible. You don’t build it to make pleasant sounds to lull you or someone else into a state of contentment. Build it to gain immediate attention. Build it and turn it on, only to hear someone say, “turn that b—dy thing orff!” By THOMAS SCARBOROUGH The inspiration for this circuit came from one of those doorbells that played the same tedious repertoire (eight tunes) over and over again. Why not, I thought, design a doorbell that would play an infinite variety of notes? Thus the idea for a random doorbell was born. But while the circuit described here will play about 20 million different sequences of notes on a single setting – most of them never previously combined, few people would actually want to use it as a doorbell, unless they were utterly tone-deaf. It sounds pretty horrible, let me tell you. Which is why this circuit rapidly “morphed” from a doorbell to a rauwww.siliconchip.com.au cous alarm. It’s now the alarm you build to get people’s attention and then, because they will hate the sound it makes, they will do whatever is required to stop the alarm. And isn’t that what you want an alarm to do? Make it awful The key to designing an effective random alarm lies in creating a series of tones which not only sound unmusical in isolation but which are musically unrelated and then produced in a random sequence. If too many random notes are played in too rapid a se­quence, one begins to approach “white noise”. If too few notes are played, or too slowly, the sound seems repetitive. The Raucous Alarm therefore plays eight notes in various sequences, and of varying duration, at a speed of about 150 beats per minute. This seemed to represent a good compromise. The Raucous Alarm is based on an RC oscillator (IC1d). It CAN be seen from the circuit diagram (Fig.1) that five resist­ances (VR2 and R4-R7) are wired in parallel to make up the value of “R” – three of these being combined more or less at random. Several resistors and capacitors set the pitch and duration of the Raucous Alarm’s notes, and any one of these could be altered to change the “fundamental” sound. I chose to make just two of these components variable, with the aim of creating the maximum variation of sound with just two adjustments, for pitch and tempo. This means that there is a fairly wide scope for variation besides that already built into the “random” circuit. The Tempo adjustment (VR1) sets the duration of four of the eight notes, while VR2 sets the amount of variation (or pitch) of the other four notes. Thus, the Raucous Alarm may be adjusted over a wide range of pitch and temJanuary 2002  77 IC1: 4093 1 14 IC2: 4066 IC1a 3 2 C 330k 4 6 VR2 220k IC2a 13 D1 IC2 PIN 14 IC2b 5 3 H 4 220k E TRIGGER INPUT: LOGIC HIGH TO F OR LINK E-F 10 9 A F 100k IC1c 8 B 22k 6 100k 8 470F 120k Q1 BUZ10 G BUZ10 S D1 1N4148 13 10F 9 22k 12 10F IC2c D VR1 1M TEMPO 10F SPKR 8 1.5W 10k 180k 5.6k D 10 IC1d 11 12 7 0.1F G IC2d D SC S 7 11 10k K 2002 +4 – 12V G D2 1N4001 2 PITCH IC1b 5 22F J 0V RAUCOUS ALARM Fig.1: the circuit is based on a Schmitt trigger oscil­lator involving IC1d. Three other Schmitt trigger oscillators control analog switches (IC2) to rapidly vary the charging re­sistance for IC1d and thus rapidly vary the frequency. po – all of which can sound pretty raucous, something like fiendish arpeggios played by a demented musician. Circuit description The Raucous Alarm makes very economical use of just a few simple components. The “economy” of this design is achieved by harnessing each of the circuit’s two ICs to fulfil more than one function. IC1, a 4093 quad 2-input NAND gate package, provides an oscillator and timer and it determines the duration of the notes. IC2, a 4066 quad analog switch, determines the pitch of the notes and also provides a buffer for the oscillator. The result is a cheap and simple circuit which produces far more (ghastly) varie­ ty than one would expect from its apparent simplicity. At the heart of the Raucous Alarm lies a simple RC oscilla­tor, based on a 2-input NAND gate IC1d (see Fig.1). “R” is deter­mined by five resistances wired in parallel, three of which are switched in and out of circuit “at 78  Silicon Chip random” by IC2a-IC2c. One of these three resistances is variable, so that more variety is added to the range of sounds produced. Diode D1, in conjunction with the series 5.6kΩ resistor, reduces the markspace ratio of the pulse waveform delivered from pin 11 of IC1d and this has the effect of reducing current con­sumption while still maintaining a high (raucous) level of sound. Switched resistors As already noted, three resistors are randomly switched in and out of the main oscillator circuit (IC1d) by analog switches IC2a-IC2c. Each of these analog switches is controlled by a sepa­rate oscillator, based on NAND gates IC1a-IC1c. Each of these oscillators uses a 10µF capacitor between the inputs and 0V while having different resistors to further “randomise” the duration of each switched “note”. Potentiometer VR1 is used in conjunction with IC1c so that the switching time for IC2c can be varied over a wide range. The fourth analog switch in the package, IC2d, actually functions as a buffer stage for oscillator IC1d. Or you could think of it as an inverter, so that each time the output of IC1d goes high, IC2d is switched to pull the gate of Mosfet Q1 low. Q1 drives the 8Ω loudspeaker directly from the positive supply rail and since it is an inductive load, diode D2 is con­nected to damp the voltage spikes that would otherwise be pro­ duced each time the Mosfet switches off. Once the Raucous Alarm has been powered up, the three oscillators based on IC1a-IC1c run continually “in the back­ground” (that is, without being heard). When the pin 13 input of IC1d is pulled high, IC1d is enabled as an oscillator and so sound (plenty of it) is heard from the speaker. Our prototype was wired with the trigger input operated by a pushbutton, by the way. When the pushbutton is pressed, just a slice of the Raucous Alarm’s continual activity is played out loud. The instant that pin 13 of IC1d is pulled high, the associated 22µF capacitor is charged up, so that oscillator IC1d is activated. After removing one’s finger from the pushbutton, the www.siliconchip.com.au 22µF capacitor discharges through the parallel 120kΩ resistor, causing a delayed “shutdown” of the Raucous Alarm. In its “background mode”, the Raucous Alarm draws around 5mA and about 160mA (at 12V) when activated. Thus a 12V plugpack rated at 200mA (about 2.5W) would suit. PITCH POT TEMPO POT Taming the output 1 D 22F TRIG IN F E 2002 IC1 10F 10F CS 4093 180k 10k 120k A 10F DC INPUT SOCKET 220k 330k K 1 D G 0.1 22k 4148 4066 G B D1 5.6k BUZ10 SPEAKER C 22k 100k 120101Q1 30 IC2 S H D2 4001 10k 100k The Raucous Alarm is very loud (nearly 2W RMS into a 8Ω speaker with a 12V DC plugpack) and will easily be heard through­out an entire home – if not by the neighbours as well! This may be reduced by wiring a resistor in series with the loudspeaker – a 220Ω 0.5W resistor will make it bearable. The alarm may also be quietened considerably by reducing the supply voltage down to as little as 4V or 5V, although this also lowers the pitch of the notes. Another thing to note is that the DC supply to the alarm should be the same as that of any external circuit which provides the trigger signal. So if it is to part of an alarm system which runs from 6V for exam- – 470F + J TEST BUTTON Fig.2: you can build this alarm as simply as you wish. Here we show it wired up with Tempo and Pitch controls and a pushbutton to sound it. Be warned - it is surprisingly loud when run from a 12V DC plugpack. SC 2002 03101021 Fig.3: above is the full-size etching pattern for the PC board, while at right is the board with all the parts installed. Note that this prototype board differs slightly from that shown in Fig.2. Resistor Colour Codes  No.   1   1   1   1   2   2   2   1 www.siliconchip.com.au Value 330kΩ 220kΩ 180kΩ 120kΩ 100kΩ 22kΩ 10kΩ 5.6kΩ 4-Band Code (1%) orange orange yellow brown red red yellow brown brown grey yellow brown brown red yellow brown brown black yellow brown red red orange brown brown black orange brown green blue red brown 5-Band Code (1%) orange orange black orange brown red red black orange brown brown grey black orange brown brown red black orange brown brown black black orange brown red red black red brown brown black black red brown green blue black brown brown January 2002  79 If you measure across Mosfet Q1 with a scope, this is the sort of waveform you can expect to see. The jitter in the wave­form is due to the rapid fluctuation (modulation) of the frequen­cy. 1 PC board, code 03102021, 74 x 49mm 1 plastic case, 148 x 80 x 48mm, or equivalent 1 2.1mm chassis-mount DC power socket 1 12V 200mA DC plugpack with 2.1mm power plug 1 8Ω loudspeaker, rated at 2W or more 10 PC pins 2 14-pin dual-in-line IC sockets (optional) 1 on-off switch (optional) 1 pushbutton switch (optional) 1 1MΩ linear potentiometer (VR1) 1 220kΩ linear potentiometer (VR2) ple, the Raucous Alarm should also run at 6V. Construction The PC board of the Raucous Alarm measures 74 x 49mm and it accommodates all the components apart from the speaker and the Tempo (VR1) and Pitch (VR2) controls. Note that VR1 and VR2 could be wired directly onto the PC board as trimpots or you could substitute fixed resistors once you have determined the values you want. Construction is straightforward – just follow the wiring diagram of Fig.2 to assemble the board and wire the speaker, potentiometers VR1 & VR2, the (optional) pushbutton and the DC socket. Component values and types will make little difference, although ICs from Motorola (the MC14093BCP and MC14066BCP) are recommended. If a BUZ10 is unavailable, any rough equivalent Mosfet such as an MTP­3055 or IRF610 can be used instead. Semiconductors 1 4093 quad NAND Schmitt trigger (IC1) 1 4066 quad analog switch (IC2) 1 BUZ10 Mosfet (Q1) 1 1N4148 diode (D1) 1 1N4001 diode (D2) Capacitors 1 470µF 16VW PC electrolytic 1 22µF 16VW PC electrolytic 3 10µF 16VW PC electrolytic 1 0.1µF MKT polyester or monolithic 80  Silicon Chip TEST TEMPO PITCH SILICON CHIP www.siliconchip.com.au Resistors (0.25W, 5%) 1 330kΩ 2 100kΩ 1 220kΩ 2 22kΩ 1 180kΩ 2 10kΩ 1 120kΩ 1 5.6kΩ Begin by fitting the 10 PC pins, the nine wire links and then the resistors. Continue with the capacitors, diodes, Q1 and finally the CMOS ICs. You can use sockets for the ICs if you wish. Note that the Mosfet and ICs are static sensitive and require appropriate handling (discharge your body to earth before handling these). Our prototype was assembled into a plastic utility box measuring 148 x 80 x 50mm. This box comfortably accommodates the PC board, the small loudspeaker and the controls. If you are using the same approach, you will need to drill holes in the lid to mount the potentiometers and pushbutton switch (if used). At one end of the case you will need to drill a hole for the DC socket and finally, you will need holes in the base of the case for the loudspeaker, to let the sound out. The case can then be fitted with four adhesive rubber feet, so that the sound RAUCOUS ALARM Parts List Fig.4: this full-size artwork can be used as a drilling template for the front panel of the Raucous Alarm. www.siliconchip.com.au Our prototype alarm was housed in a plastic box with Tempo and Pitch controls but it does not need to be that complicated. SMART FASTCHARGERS® 2 NEW MODELS WITH OPTIONS TO SUIT YOUR NEEDS & BUDGET Now with 240V AC + 12V DC operation PLUS fully automatic voltage detection Use these REFLEX® chargers for all your Nicads and NIMH batteries: Power tools  Torches  Radio equip.  Mobile phones  Video cameras  Field test instruments  RC models incl. indoor flight  Laptops  Photographic equip.  Toys  Others  Rugged, compact and very portable. Designed for maximum battery capacity and longest battery life. AVOIDS THE WELL KNOWN MEMORY EFFECT. SAVES MONEY & TIME: Restore most Nicads with memory effect to capacity. 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If desired, an on-off switch can be inserted in the posi­tive supply line, or you can simply pull out the power plug when you wish to silence it. Using it No special setup is required for the Raucous Alarm. It is ready to go as soon as the power is plugged in. However, you might wish to begin as follows. First, turn the two front-panel potentiometers roughly to their mid-positions, then plug in a 12V 200mA (or greater) power supply. Note www.siliconchip.com.au that the centre pin must be positive, otherwise damage could result. If in doubt, check this with a multimeter before plugging it in. Now press pushbutton S1. Every press of the pushbutton should yield a different sequence of notes. Beware – the Raucous Alarm has an ear-piercing volume! If the unit does not function as described, unplug the power immediately and recheck the wiring. Most faults are missed solder joints, diodes in the wrong way or shorts due to solder splashes on the copper side of the PC board. Now experiment with front panel controls VR1 and VR2. VR1 adjusts the sound from a sedate to a lively warble, while VR2 alters the pitch of half of the notes, from sequences that sound something like standard scales, to much more varied arpeggios. SC • • • • • If you need: P.C.B. High Speed Drill 3M Scotchmark Laser Labels P.C.B. Material – Negative or Positive acting Light Box – Single or Double Sided – Large or Small Etch Tank – Bubble Electronic Components and Equipment for TAFEs, Colleges and Schools Prompt and Economical Delivery FREE ADVICE ON ANY OF OUR PRODUCTS FROM DEDICATED PEOPLE WITH HANDS-ON EXPERIENCE We now stock Hawera Carbide Tool Bits KALEX 40 Wallis Ave E. Ivanhoe 3079 Ph (03) 9497 3422 FAX (03) 9499 2381 ALL MAJOR CREDIT CARDS ACCEPTED January 2002  81