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SCENE E H T : 1 IT IB H X E OF THE CRIME Simple circuit uses a PIR sensor to detect movement. Use it as a cat deterrent, door minder or burglar alarm . . . EXHIBIT 2: MISCREANTTHE The NickNick-O Off Bad Cat Deterrent Do you have a miscreant “puddy-tat” that likes to jump on kitchen benches (or worse)? It can be a real problem, especially at night when no-one is looking. The Nick-Off Cat Deterrent (aka the Ted-Off) is the perfect solution. It uses an infrared sensor to detect said cat and triggers an answering machine to play back simulated, demented barking. It also lights two white LEDs which form the eyes of an angry dog. A LLOW US TO introduce Ted. Ted is a 13-year-old black-and-white de-sexed male moggie and is the muchloved pet of a family friend. According to his owner, Ted’s had 13 years of practice getting humans to do exactly what he wants them to do. Want to be fed? Make a first-rate nuisance of yourself until a human complies with the goodies. Want to 62  Silicon Chip go outside? Dig your claws into the screen door, or claw the carpet or start ripping the newspaper under the food bowl to shreds. Any one of those actions is absolutely guaranteed to attract attention and gain the necessary compliance from Ted’s owner. Apart from that and some minor indiscretions such as the occasional fight (and a trip to the vet for repairs), Ted has been relatively trouble-free. Until recently, that is, when Ted developed a rather revolting habit. You see, Ted has the run of a downstairs living area at night, comprising a kitchen/dining room, a rumpus room and the laundry (with his litter tray). But just recently, after 13 years of being a good pussy cat, Ted suddenly decided that he was going to jump siliconchip.com.au EXHIBIT 3: THE PURRRFECT SOLUTION!!! Article: Greg Swain Circuit : Nicholas Vinen up on the kitchen bench at night and scent-mark the glass splashback in one particular corner of the kitchen. The result each morning was a smelly liquid pool that had to be thoroughly cleaned up and the splashback and benchtop washed down with disinfectant – not a pleasant job. And he didn’t do it just a few times. Having started the practice, it quickly became a habit, much to his owner’s disgust and annoyance. Ted’s human has a theory as to why he suddenly started doing this. Just before the first incident, he had been shoved into a pet box and unceremoniously carted off to the vet for his annual flu injection. And while he was waiting for said injection, Ted had been forced to share the waiting room with a rather boisterous and over-friendly Labrador. Ted was not at all impressed with this and the subsequent flu injection only added to his trauma and bad temper. Having had his jab, he was taken home and released from the confines of his pet box, whereupon siliconchip.com.au he immediately made plain his considerable displeasure by attacking his scratching post. And then that night, the indiscretions started. Perhaps it was Ted’s revenge for the vet trip or perhaps it was to re-establish territory and to let everyone know who really was the boss. But whatever the explanation, the result was . . . uggghhhh!! A solution Shortly after he started his shenanigans, Ted’s owner asked me if I knew of an electronic device, perhaps an alarm, that would keep him off the bench. A quick search on Google soon revealed the “Ssscat”, a battery-powered device that combines a motion detector (presumably a PIR sensor) with a can of harmless, odourless spray. The device detects the cat’s movement out to about 1m and releases a brisk spray to warn the cat off. That got me thinking. I had a spare PIR (passive infrared) sensor, as used in burglar alarm systems, plus an old analog telephone answering machine It Has Other Uses This circuit is basically a simple movement detector/alarm circuit with a 30s exit delay and two outputs: one to simulate a button press and the other to drive two series LEDs or a relay (or some other load) for an adjustable period ranging up to 60s. As such, it could also be used as a shop minder or as a simple, low-cost burglar alarm for a garage. Or it could be used just to trigger a message machine or activate some other device when movement is detected (eg, close to a display counter). You don’t have to use a PIR sensor to trigger the device either. The Nick-Off can be used with virtually any sensor that features NC or NO contacts, eg, a reed switch or pressure mat. tucked away in a drawer. Could I combine them somehow so that the PIR sensor triggered the answering machine when movement was detected? As with most telephone answering machines, this one had a message October 2012  63 D1 1N4004 POWER SWITCH A Q1 2N7000 K 1 1 2 A RLY2 –PWR 1 LK1* 2 D3 1N4148 VR1 A 500k 1M 10M 4 4 LK2 2 10nF LK4 LK3* RST1 1 13 12 Trig1 RST2 1M 100nF CV1 1M 180 D4 1N4148 Out2 9 A 10nF A K 10nF Thrsh2 Trig2 3 CV2 GND 7 11 NICK-OFF CAT DETERRENT  LED1 K 2 A  LED2 10nF 1 EXT LEDS CON3 K *NOTE: INSTALL LK1 & LK3 FOR NC (NORMALLY CLOSED) PIR RELAY CONTACTS, OR LK2 & LK4 FOR NO (NORMALLY OPEN) CONTACTS SC CON2 5 IC1 556 Disch2 8 10k Out1 Thrsh1 10 100F 100F 14 Vcc Disch1 6 3 CON1 2012 TO PLAYBACK BUTTON K 10k RLY1 2 2.2k 470F +PWR 1 G K D2 1N4004 K TO PIR DETECTOR 100nF 100F CON5 CON4 POWER  LED3 2 D S A LEDS 1N4004 1N4148 A A K K K A 2N7000 G D S Fig.1: the circuit is based on IC1, a 556 dual-timer IC. This is triggered by the PIR and generates a short pulse to trigger the answering machine via Mosfet Q1 and a longer pulse (up to 60s) to drive two high-brightness LEDs (LEDs1 & 2). pushbutton that you momentarily press to play back the recorded message. In theory, it would be just a matter of processing the output from the PIR sensor to simulate this button press. A simple transistor circuit was quickly lashed up on stripboard and this proved the basic concept. This circuit detected when the NC (normallyclosed) relay contacts in the PIR sensor opened (ie, when movement was detected) and produced a brief low-going pulse at its output. This output was wired across the message button in the answering machine (to simulate the button press) and it worked like a charm. By then recording a suitably scary barking sound on the answering machine, it just might do the trick. In practice, this was more of a demented WOOF WOOF WOOF WOOF WOOF . . . Get-Ooorrrf-There-Ted . . . WOOF WOOF WOOF Grrrr WOOF WOOF sequence, which I imagined would have the desired effect. Introducing the Ted-Off Having established that the circuit worked, I decided to build the proto64  Silicon Chip type into a spare biscuit tin, with the PIR sensor attached to one side. At the same time, a scary bulldog graphic was also added to the lid, along with a couple of white LEDs for his eyes. These LEDs required an extra transistor and lit up for around 30s each time the device was activated. And so was born the “Ted-Off”, named in honour of the miscreant himself. It was duly installed in my friend’s kitchen for its maiden run. Did it work? Ted was nailed by the Ted-Off on the very first night. At 3.15 in the morning. Just when you would least expect it. As Ted’s owner put it, the demented barking sound from the answering machine, at full volume, in the middle of the night was enough to awaken the dead. Her first thought was “what the hell’s that?” and then, having realised what it was, she rushed down the stairs and opened the door into the kitchen . . . just in time to spy Ted’s hindquarters disappearing under one of the chairs around the dining table. Eureka!! – it had worked and there wasn’t a scent mark anywhere. Not only that but it has since proved to be a very effective deterrent. After the shock of that first encounter, Ted behaved himself for quite some time before getting sprung again about 10 days later. And that was it – despite several months having now passed, the Ted-Off has since remained mute and Ted has kept out of the kitchen at night. According to his owner, just having the device sitting on the kitchen bench is now probably enough to deter him, whether it’s powered or not. The Nick-Off version For the version described here, we decided to do away with the messy transistor circuit which admittedly had a few whiskers on it (pun intended). Instead, our resident genius Nicholas Vinen came up with a new circuit based on a dual-timer IC and designed a PCB to make the assembly easy. The result is the “Nick-Off”, a more generic name than “Ted-Off”. In reality, the Nick-Off is Ted-Off Mk.2 and it’s built into the original Ted-Off biscuit tin. Even the original front-panel label has been retained. We simply siliconchip.com.au Switching A Relay Output Normally, you will install either the onboard output LEDs (LED1 & LED2) or wire an external pair of white or blue LEDs to CON3. However, you can also use this circuit to switch a relay which can then turn on a variety of other devices. Fig.2 shows how this is done. The relay coil voltage should be chosen to match the unit’s supply voltage, while the 180Ω series resistor from pin 5 of IC1 is replaced with a wire link. The additional diode is required to absorb any back-EMF from the relay coil when it is de-energised (you may be able to solder this diode across the pads for LEDs1 & 2). removed the original transistor circuit and installed the new (and improved) circuit in its place. As with the original circuit, the Nick-Off processes the output from a PIR sensor and generates a brief (about 100ms) low-going pulse to trigger an answering machine (or you could trigger the Digital Sound Effects Module described last month). It also has a second output to drive the two highbrightness LEDs (the dog’s eyes) for a period that’s adjustable anywhere between a fraction of a second up to about 60 seconds. This output could also be used to trigger a buzzer or a relay, or some other low-voltage device (see panel). The Nick-Off also features an exit delay, something lacking on the original Ted-Off. This exit delay is normally around 30s but is less than this (about 10s) if the device is switched off and then immediately switched on again. In addition, the Nick-Off caters for both NC (normally closed) and NO (normally open) sensors, whereas the original transistor circuit worked with NC sensors only. Circuit description Take a look at now at Fig.1 which shows the circuit diagram. It’s based on IC1, a 556 dual timer IC. The PIR sensor is wired to 4-way terminal block CON1, at left. This provides power to the PIR from pins 1 & 4, while the PIR’s output relay contacts are connected to pins 2 & 3. When triggered, the PIR activates IC1 which in turn drives the white LEDs and activates the answering machine (via Mosfet Q1). The PIR signal is AC-coupled to siliconchip.com.au 14 Vcc Out1 CV1 180  RESISTOR REPLACED BY WIRE LINK 5 3 D2 1N4148 IC1 556 Out2 9 A 10nF K 10nF CV2 GND 7 RELAY COIL CONNECTED TO CON3 180 11 10nF IC1 via a 10nF capacitor and a 1MΩ pull-up resistor, so that the trigger pulse is kept short (about 50ms). This ensures that IC1 is not immediately re-triggered if the PIR stays on for the entire duration of the timing period (eg, if there is constant motion in front of the sensor). Instead, IC1 can only be retriggered by a new event after it has timed out. Some PIRs have normally open (NO) contacts, which close when activated by motion, but most have normally closed (NC) contacts which open when motion is detected. In addition, a few PIRs have both NO and NC contacts available. Our circuit caters for both types of contacts using links LK1-LK4 and two 10kΩ resistors. One of these resistors acts as a pull-up, while the other acts as a pull-down. Links LK1 & LK3 are installed for PIRs with NC contacts. This means that the lefthand side of the 10nF capacitor is normally pulled up to the positive supply rail (Vcc) via LK3, the closed relay contacts and LK1. However, when the contacts open (ie, movement is detected), this side of the 10nF capacitor is pulled down via LK3 and the lower 10kΩ resistor, thereby generating a brief pulse and triggering IC1. Conversely, for a PIR with NO relay outputs, links LK2 & LK4 are installed. The lefthand side of the 10nF capacitor is then normally pulled high via LK2 and the upper 10kΩ resistor. When motion is detected and the contacts close, this side of the capacitor is pulled down via LK2, the relay contacts and LK4, again generating a brief pulse that triggers IC1. IC1 is configured as two monosta-  LED1 RELAY D4 1N4004 CON3  LED2 K 2 1 A LED1 & LED2 OMITTED ble pulse generators but let’s initially concentrate on timer 1. When this is triggered, its pin 5 output (Out1) goes high, supplying power to two white LEDs (LED1 & LED2) via a 180Ω current-limiting resistor. The duration that they are lit for is set by 500kΩ trimpot VR1 and a 100µF timing capacitor. VR1 allows this duration to be set anywhere from a fraction of a second up to about one minute. LEDs1 & 2 are high-brightness 5mm white LEDs and the 180Ω series resistor limits the current through them to (12V - 2 x 3.3V) ÷ 180Ω = 30mA (assuming a 12V supply). This will vary depending on the supply voltage and the forward voltage of these LEDs. It’s obviously lower for a 9V supply, although the LEDs will still be quite bright. To prevent the timer from being triggered when you first apply power to the unit, the reset input (pin 4) of timer 1 is initially held low via a 100µF capacitor. This then slowly charges via a 10MΩ resistor and the reset is subsequently released (goes high) about 30s after power is applied. This provides the “exit delay”. When the unit is switched off, the 100µF reset capacitor quickly discharges via diode D3 so that the exit delay operates if the unit is quickly switched on again. Note, however, that D3 only initially discharges this capacitor down to about 0.5V. IC1’s reset threshold is around 0.7V so if the unit is switched off and then immediately switched on again, the exit delay will be shorter than usual (about 10s). Triggering sound The second half (timer 2) of IC1 is October 2012  65 + LED1 Specifications • • Power Supply: 9-12V DC Exit Delay: 30s (less if unit is switched off and on again quickly) • Can be triggered by both NC & NO contacts on alarm sensors • 100ms pulse output to trigger an answering machine or sound module • Second output to drive high-bright­ ness LEDs (or some other load) for up to 60s (adjustable) used to generate a short pulse to trigger a telephone answering machine. As shown on Fig.1, connector CON2 is wired to the trigger input of the sound playback device. Pin 1 of this connector is briefly pulled low when a sound is to be played. For our prototype, we wired CON2 across the playback pushbutton of a telephone answering machine. However, we could have just as easily used the Sound Effects Generator module described in September 2012, which also has open-collector compatible trigger inputs by default. In operation, timer 2 in IC1 is triggered by timer 1. It works like this: when the pin 5 output of IC1 goes high 100nF CON2 2 100nF D4 4148 LEDs 2102 C LED2 TO PLAYBACK BUTTON 1 10nF 10nF 180 1M 1M LK4 Q1 CON3 NC + 100F NO NC LK1 NO 0V – CON1 +12V + IC1 556 D2 + 470F CONTACTS PIR SENSOR + D3 4148 10M 4004 10k 1M – 10nF 9-12V DC SUPPLY LED3 500k 2.2k 4004 D1 10nF 100F CON4 + 100F VR1 10k 12101130 CON5 SWITCH POWER SWITCH CONNECTS TO THESE PINS 1 2 TO EXTERNAL LEDS + – Fig.3: follow this diagram and the photo to build the PCB (note: photo shows a prototype PCB) to drive the white LEDs, a positivegoing pulse is also AC-coupled to the threshold pin (pin 12) of timer 2, again via a 10nF capacitor and a 1MΩ resistor. Normally, a 556 (or a 555) timer is triggered using a negative-going pulse but it’s also possible to use a positive trigger by simply swapping the trigger and threshold pins (pins 8 & 12). In this case, the output sense is inverted and the timing capacitor (100nF) is normally charged and discharges while the timer is active (rather than the reverse situation). Timer 1 is used to trigger timer 2 so that the latter can’t be re-triggered until timer 1 has reset. This ensures that, provided VR1 is suitably adjusted to set the period of timer 1, a second trigger event cannot cancel or restart the playback, especially if the playback period is quite long. In practice, it’s just a matter of adjusting VR1 so that the white LEDs are on for longer than the sound playback period. The main wrinkle with the configuration of timer 2 is that there is no dedicated pin to recharge the timing capacitor. However, that’s easily solved with the addition of diode D4, which allows the timing capacitor to charge directly from the timer output at pin 9 (which is high when the timer is reset). In this case, the timing capacitor is 100nF and the discharge resistor is 1MΩ, giving a time constant very close to 100ms (0.1s). When the circuit is first powered up, the 100nF timing capacitor is initially discharged and so trigger pin Trig2 (pin 8) is initially low. This effectively resets the timer 2 and its output at pin 9 goes high, which is its quiescent state. When timer 2 is triggered (ie, by timer 1), its output goes low but more importantly, so does its discharge pin (pin 13). This pin is used as an open-collector output to trigger the playback device. Mosfet Q1 There is a bit of a problem with this scheme, though. While the timer is set up to be immediately triggered, during power-up and power-down when the supply voltage is very low (<3V), IC1 is automatically reset by its internal circuitry. At this time, the discharge pin (pin 13) sinks current regardless Table 2: Capacitor Codes Value µF Value IEC Code EIA Code 100nF 0.1µF 100n 104 10nF 0.01µF   10n 103 Table 1: Resistor Colour Codes o o o o o o No.   1   3   2   1   1 66  Silicon Chip Value 10MΩ 1MΩ 10kΩ 2.2kΩ 180Ω 4-Band Code (1%) brown black blue brown brown black green brown brown black orange brown red red red brown brown grey brown brown 5-Band Code (1%) brown black black green brown brown black black yellow brown brown black black red brown red red black brown brown brown grey black black brown siliconchip.com.au Connecting The Message Button In The Answering Machine T HE ANSWERING machine is connected via a 2-wire cable that’s wired across the message button and runs back to the Nick-Off via a 3.5mm mono jack plug. You will have to split the case of the answering machine in order to get at the message button. That’s normally done by undoing a few self-tapping screws. In our case, we also removed one of the telephone sockets at the rear of the machine (since this was no longer required) and fed the 2-wire cable in through the vacant hole. Before wiring in the playback cable, use a DMM to identify which side of the message button connects to ground (0V). This side of the button must be connected to the ground terminal (2) of CON2 in the Nick-Off (ie, via the ground side of the jack socket). This is shown in Fig.2 as the black wire on CON2. The other side of the button goes to terminal 1 of CON2 in the Nick-Off (blue wire). In our case, the ground wire running into the answering machine was soldered to a ground stake that was of the state of the trigger and threshold inputs. As a result, we have added Mosfet Q1 between the discharge pin and playback button connector (CON2) to prevent false triggering. This works as follows. First, LED3 acts as both a power indicator and as a simple shunt regulator. It is a blue LED and so has a typical forward voltage of 3-3.6V. Its anode is connected to the positive supply rail and its cathode to the gate of Q1, as well as its 2.2kΩ current-limiting resistor. Q1 needs a gate voltage of around 1-2V above its source in order to switch on. This means that it remains off until the supply voltage rises to about 3.3V + 1V = 4.3V. It’s also off if the supply voltage falls below 4.3V (ie, during switch-off). This prevents false triggering when power is applied or removed. Note that if you change the colour of LED3 to a type which has a lower forward voltage (eg, green, red, yellow or orange), then Mosfet Q1 may turn on prematurely and you could get false triggering at power-up and/or powerdown. The same comment applies if siliconchip.com.au EARTH STAKE MESSAGE BUTTON already present on the PCB at the rear of the machine. The other wire was run to the front of the answering machine and soldered directly to one of the message switch contacts on the top of the board. In some answering machines though, it may be necessary to remove the PCB in order to get at the LED3 is disconnected or not installed, so don’t leave this part out of circuit. Supply components IC1’s two control voltage terminals (CV1 and CV2) have the recommended 10nF bypass capacitors. These filter IC1’s internal 2/3 supply voltage dividers, giving it better rejection of supply voltage variations. Diode D1 provides reverse supply polarity protection for the timer circuit. The resulting supply rail is then filtered using a 100µF capacitor. Diode D2 serves two purposes. First, it provides reverse polarity protection for the supply to the PIR sensor and second, it isolates this supply from the timer supply rail. As a result, at switch-off, the supply rail to the PIR is maintained for longer than the supply rail to IC1. This prevents the relay contacts in the PIR sensor from opening prematurely and false triggering the timer circuit and thus the answering machine (assuming that it has an NC output). Because of D2, the PIR’s supply switch contacts. If so, it’s usually just a matter of removing a few more selftapping screws. Make sure you correctly identify the switch contacts – the ground contact must run back to the ground in the Nick-Off. If you get the wires mixed up, you could damage the answering machine’s playback circuit. rail will be about 0.7V less than the external supply voltage. However, this shouldn’t be an issue. CON5 is a 2-pin header that’s wired in series with the external supply. It can either be fitted with a jumper link so that the circuit is permanently powered or wired to an external power switch. The power supply is fed in via 2-way terminal block CON4. PCB assembly Take a look now at Figs.3 & 4 for the assembly details. All the parts, with the possible exception of the LEDs and power switch, are mounted on a small PCB coded 03110121. There are a few options when it comes to the PCB assembly. First of all, you can either mount LEDs1 & 2 directly on the board or you can mount them externally (ie, connect them in series) and run flying leads back to screw terminal block CON3. Similarly, power indicator LED3 can either be mounted directly on the PCB or connected via flying leads. There are also several power switch October 2012  67 There’s plenty of room inside the tin to accommodate call the bits. Note the old doorstop sitting in the bottom of the tin – it’s full of old nuts and bolts and acts as a weight to provide stability. Fig.4: the Nick-Off PCB is installed in a biscuit tin and wired up as shown in the diagram at right. Be sure to use a blue LED for the power indicator, as this is necessary to ensure correct operation of Mosfet Q1. The four leads from the PIR sensor are fed in through a hole drilled in the back of the tin. A P-clamp keeps the wiring in place. 68  Silicon Chip options. If you don’t need an on/off (power) switch, you can simply install a wire link in place of CON5 or you can fit a 2-way pin header and install a jumper link. Conversely, if you do need an on/off switch, then it’s simply a matter of connecting it via flying leads, either via a female header or by soldering the switch leads to the header pins. No particular order need be followed with the PCB assembly, although it’s best to start with the low-profile parts (resistors and diodes) first and finish with the connectors. Take care with the orientation of the IC, diodes, LEDs and electrolytic capacitors and leave siliconchip.com.au 4148 – 4004 CON2 LED3 CON4 + + 12101130 CON5 S1 POWER SWITCH 2 K 1 A 0V + CON3 NO NO CON1 OUTPUTS + NC 12V NC + 4148 + 4004 BLUE POWER LED LED1 1 2 TO 2 x 5mm WHITE LEDS WIRED IN SERIES – & MOUNTED ON LID + 2102 C LED2 PCB TO PIR DETECTOR TIP TERMINAL 3.5mm MONO JACK TO PLAYBACK BUTTON COLLAR – + 2 x 2.1mm DC POWER SOCKETS WIRED IN PARALLEL the LEDs off the board if you intend mounting them externally. A 2-way pin header (similar to CON5) can be substituted for LED3 to make any external wiring connections to this LED easier. Do not leave LED3 out and be sure to use a blue LED. Note particularly the orientation of IC1. It must be installed with its notched end towards VR1. It can be soldered directly to the PCB, or you can mount it via a socket if you wish. Once the PCB has been assembled, you need to fit jumpers to the LK1-LK4 positions to suit your PIR detector. If the detector has NC (normally closed) contacts, then fit jumpers to the two NC siliconchip.com.au pin headers (LK1 & LK3). Conversely, if your PIR has NO (normally open) contacts, fit the jumpers to the NO headers (LK2 & LK4). Note that some PIR sensors have both NC and NO contacts available. The NC contacts open when movement is detected, while the NO contacts close when movement is detected. In that case, it’s just a matter of choosing either contact set and installing the LK1-LK4 jumpers accordingly. Housing it As stated earlier, the original TedOff (now the Nick-Off) was built into a biscuit tin, with the bulldog artwork mounted on the lid. This not only maintains a kitchen theme but also saves you forking out extra dollars for a case. That’s assuming, of course, that you already have a biscuit tin and have eaten all the biscuits. The biscuit tin used for the prototype measures 190mm in diameter, which is pretty much standard. The size isn’t critical – just as long you can get all the bits in. An inverted plastic dinner plate (as used for barbecues) was used for the base. Anything around 160-170mm diameter is suitable and it’s secured to the bottom edge of the biscuit tin via three M3 x 15mm machine screws October 2012  69 Preventing False Triggering When The Unit Is Switched Off V IRTUALLY ALL PIR sensors have an NC (normally-closed) output in the quiescent state. This output is usually provided by a relay that’s energised to close a pair of contacts when the PIR sensor is powered but no movement is detected. This scheme is employed to help make the sensor tamper proof. If the power supply to the sensor is cut, the relay opens and triggers an alarm module, just as if movement had been detected. One problem we encountered in developing this unit was that the answering machine (which was separately powered) false-triggered whenever the Nick-Off was switched off. The reason for this was simple: when we cut the power to the Nick-Off and thus to the PIR sensor, the relay in the sensor immediately opened its contacts. This was then detected as a valid trigger pulse by IC1 which had yet to completely power down (the 100µF supply bypass capacitor takes time to discharge). As a result, the timer generated an output pulse which triggered the answering machine. We overcame that problem by isolating the supply rail to the PIR sensor using diode D2 and then bypassing this rail with a 470μF capacitor. That way, after switch-off, the supply rail to the PIR sensor remains intact for a period that’s long enough for the timer circuit to power down, ie, before the relay contacts eventually open. If you find that your unit still false triggers, it’s just a matter of reducing the 100μF bypass capacitor between D1’s cathode and ground, eg, to 47μF or 22μF. Alternatively, in some cases, you might want to keep the PIR sensor permanently powered and just switch the timer circuitry on and off. That can be done by simply connecting the positive supply lead from the PIR sensor direct to pin 1 of CON4 or to the supply side of the power switch. the prototype, it didn’t quite work out that way because the answering machine plugpack couldn’t supply the necessary juice to power both the answering machine and the Nick-Off. The extra current required by the PIR sensor, particularly when activated, was probably the main culprit here. As a result, the prototype Nick-Off had to be powered by a separate 9V DC plugpack. Mounting the PIR sensor The PIR sensor is attached to the side of the tin using hook and loop material (Velcro), while the rubber foot stops it from rotating. At the rear, the cable from the answering machine is connected via a 3.5mm jack plug and socket. arranged in a tripod formation (two at the front and one centred between them at the back). You will need to use a couple of M3 nuts as spacers on the two front screws to compensate for the curvature of the tin. The bulldog artwork (available on the SILICON CHIP website) is secured to the lid using double-sided tape, after which two 5mm holes are drilled through the dog’s eyes to accommodate the external white LEDs. On the prototype, these were secured in place using neutral-cure silicone sealant. Alternatively, you can make the holes slightly larger and secure the LEDs using plastic mounting bezels. Fig.4 shows the wiring details. The PCB was mounted on three M3 x 10mm 70  Silicon Chip tapped Nylon spacers and it’s simply a matter of drilling matching holes through the base (rear) of the tin. In addition, you have to mount a 3.5mm mono jack socket (to plug in the cable from the answering machine) and two 2.1mm panel-mount DC sockets towards the bottom. The DC sockets are wired in parallel to provide power “pass-through”. That way, you can use the answering machine plugpack (provided it’s rated at 9-12V DC) to power both the NickOff and the answering machine. You will have to make up a cable fitted with DC plugs at both ends to connect the answering machine to one of these sockets. Well, that’s the theory anyway. On As shown in the photos, the PIR sensor is secured to the lefthand side of the tin using hook and loop material, eg, Velcro (available from hardware stores). This consists of two 15mmdiameter pads, one attached to the side of the tin and the other to the side of the sensor. In addition, a rubber foot is secured to the side of the tin about 50mm away from the pad, using an M3 x 10mm machine screw nut and washer. This foot provides a “rest” for the bottom righthand edge of the sensor and ensures that it stays upright. Without this rest, the sensor tends to rotate (or “sag”) anticlockwise. The four wires from the PIR sensor are fed in via a hole drilled in the rear of the tin and are connected to CON1. Alternatively, the PIR can be permanently powered by connecting its positive supply lead direct to the supply side of the power switch. Testing Once the assembly is complete, apply power (without the answering machine connected) and check that siliconchip.com.au Parts List 1 PCB, code 03110121, 50 x 50mm 5 2-way mini terminal blocks, 5/5.08mm pitch (CON1-4) 5 2-way pin headers, 2.54mm pitch (LK1-LK4, CON5) 3 shorting blocks 1 500kΩ mini horizontal trimpot 1 2-way header plug, 2.54mm pitch (CON5) (optional) What’s new pussycat? – the original Ted-Off, proudly standing guard in the kitchen. the blue power LED lights. The two white LEDs (LEDs 1 & 2) should be off at this stage. If the power LED doesn’t light, check the supply polarity and that D1 and LED3 are correctly orientated. Assuming that all is correct, switch off and check that you have the correct linking options for LK1-LK4. In most cases, you will need to install links in the NC positions (ie, LK1 & LK3) if you are using a PIR sensor. That done, reapply power and wait for the exit delay (up to 30s) to expire. In addition, PIR sensors require a warm-up period of up to two minutes before they start working, so you will have to wait this period out if it’s longer than the exit delay. siliconchip.com.au Once the PIR sensor is operational, move in front of it so that it triggers and check that the two white LEDs immediately light up. These should then stay on for a preset period (up to 60s), depending on the setting of VR1. Adjust VR1 to suit your particular application. Finally, plug in the answering machine, switch it on and re-trigger the PIR. The two LEDs should again immediately light up and the answering machine should trigger and play back the recorded message (or barking). If that all works, the Nick-Off is ready for action and can be set on the kitchen bench to watch out for errant puddy tats. And that is the end of this SC tail . . . err, tale. Semiconductors 1 556 dual timer IC (IC1) 1 2N7000 Mosfet (Q1) 2 1N4004 diodes (D1, D2) 2 1N4148 diodes (D3, D4) 2 white high-brightness 5mm LEDs (LED1, LED2) 1 blue 5mm LED (LED3) Capacitors 1 470µF 16V electrolytic 3 100µF 16V electrolytic 2 100nF MKT/MMC 4 10nF MKT/MMC Resistors (0.25W, 5%) 1 10MΩ 1 2.2kΩ 3 1MΩ 1 180Ω 2 10kΩ Extra Parts For Nick-Off 1 telephone answering-machine or electronically-triggered sound generator module 1 9-12V 300mA DC plugpack 1 PIR sensor (9-12V) 1 biscuit tin, 190mm diameter 1 plastic dinner plate, 160mm diameter (approx.) 1 front panel artwork (available from siliconchip.com.au) 1 chassis-mount toggle switch 2 2.1mm panel-mount DC sockets 1 3.5mm mono jack socket & plug 3 5mm plastic LED bezels 1 Nylon P-clamp, 5mm 3 M3 x 10mm tapped Nylon spacers 1 rubber foot (screw-mount) Hook & loop material (15mm-dia. pads) 6 small cable ties 1 M4 x 10mm machine screw 1 M4 nut 1 M4 flat washer 3 M3 x 15mm machine screws 1 M3 x 10mm machine screw 6 M3 x 6mm machine screws 8 M3 nuts 8 M3 flat washers 3 300mm lengths of medium-duty hook-up wire (red, black & blue) October 2012  71