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A cheap’n’easy MOTORBIKE ALARM Design by Mick Gergos* With car manufacturers (finally!) getting smarter with security, motorbikes often make a “softer” target for thieves. Here’s an alarm which is very simple to build, very simple to fit to almost any ’bike – and very easy to operate. Arming and disarming is done with the ignition key! www.siliconchip.com.au January 2002  53 M any motorbikes today cost almost as much as – and of ten more than – a small car. Their value and their mobility makes them targets for thieves – whether joyriders (hate that word – there’s no joy for the owner!) or professional crooks. It’s somewhat surprising then to find how few ’bikes are fitted with alarm systems. That’s probably because alarms for bikes have been in the “too hard” basket – they are exposed to the weather (with all the problems that creates); they are vulnerable because they can’t be hidden “inside”; they are too big for a small bike; you can’t hide operating switches; you need to get at the wiring harness . . . and so on. Here’s a motorbike alarm which addresses all those problems and more. It’s heatshrunk to protect it, it’s tiny enough to be hidden just about anywhere, it doesn’t need any external controls – and it suits virtually all ’bikes. As long as they have a battery and a headlight, this alarm should suit. The alarm is “armed” automatically. When you turn the ignition off, you have 20 seconds to get off the bike. After this time, if anyone attempts to get on the bike or move it, they’ll hear a series of warning “chirps” followed by four seconds of quiet. It’s then in a “heightened alarm” state: touch it again within 30 seconds or so and the alarm screams its head off for 45 seconds! If someone is still trying to interfere with the bike, the cycle will repeat three times (giving 3 x 45 second alarms). It won’t keep continually going off because noise pollution laws in most states prohibit this. If it is not touched again within the 30-second heightened alarm state, it goes “back to sleep” and waits for the next person to have a go. To turn the alarm off while it is sounding, you simply turn the ignition key on then off. This resets and rearms the alarm. But what if you don’t want the alarm on, for some reason? That’s easy: you simply turn the ignition key on and off twice – ie, on-off-on-off. This resets the alarm but disables it – and tells you with an acknowledgement “chirp”. Next time you turn the ignition on, you will reset the alarm again ready for use when the ignition is turned off again. As you can see, operation is foolproof and all done with the ignition key – there are no hidden switches to worry about, no keypads to go faulty – nothing except the ignition switch. And if that goes faulty, you have a few more problems than an alarm that doesn’t work! The sensor Two types of sensor are recommended – you can choose either or both if you want a belts-and-braces approach. The first is a non-position-sensitive motion detector which simply detects any movement of the bike. The second is a mercury switch, arranged as a “tilt” switch: when the ‘’bike is on its stand, the mercury switch is positioned so it doesn’t conduct. Take if off the stand, or move it in some other way and the switch does conduct. Both of these switches are “normally open” types so, if you wish, you can fit one (or even more) of each type in parallel. How it works The circuit itself is very simple because, once again, a microcontroller does most of the work. First, though, let’s look at the supply. As you will note from the circuit, there is a connection to the ‘+’ side of the ’bike’s battery but no apparent connection to the ‘–’ side. How come? What would normally be regarded as the ‘–’ or chassis connection is in fact connected between the light switch and the headlight. When the headlight is switched off, there is a low-resistance path (through the headlight filament) to chassis. If, say, the headlight is 50W, from Ohm’s law we can work out that the resistance of the filament is about 3Ω (in fact it’s much less than this when it is cold). The complete alarm, shown with a small piezo siren which can be mounted anywhere on the bike with access to free air (so the sound isn’t muffled). Just keep in mind that most piezos don’t like water one little bit! 54  Silicon Chip www.siliconchip.com.au BATTERY + Parts List – Motorcycle Alarm HORN + D1 1N4007 IC1 12C508A REG1 78L05 OUT IN HORN GND 4 3 2 GP3 VDD B 6 1k 5 GP4 GP5 GP1 VSS GP0 7 C E Q1 MJE3055 GP2 120k D2 1N4148 8 0.1F 1 PC board, 38 x 20mm, code 05101021 (OR Veroboard, 10 tracks x 18 holes – see text) 1 60mm length 30mm heatshrink 1 cable clamp 1 motion detector switch AND/OR mercury switch – see text 1 piezo siren (Jaycar LA5225 or similar – see text) Suitable lengths automotive wire 1 COM 0.1F* 10F TANT HEADLIGHT (+) *MOUNTS ON COPPER SIDE OF PC BOARD SW1: SHOCK/TILT SENSOR SWITCH 78L05 MJE3055 C SC 2002 MOTORCYCLE ALARM IN OUT COM B C E It couldn’t be much simpler: just ten components make up the motorcycle alarm. That amount of resistance to chassis won’t affect the operation of this circuit at all. If both the headlight and ignition are switched on, both supply lines are at the same potential, so the alarm is disabled. Back to the supply again: it passes through a polarity-protection diode (just in case!), and then a 5V regulator to give IC1 the voltage it requires. It also goes direct to the horn or siren ‘+’ side, with a hefty transistor, controlled by the microcontroller, switching its ‘–’ side. This transistor is extreme overkill given the likely current of the horn or siren but this is one component you would not like to see go short circuit! The output current switched by this transistor mustn’t exceed 1A anyway, because that’s the rating of the reverse-polarity protection diode. (Most piezo sirens would draw only a couple of hundred milliamps or so). Every time the microcontroller is powered up, it looks for a “high” from its 1-bit external memory device (the 10µF tantalum capacitor). If it is not high, the PIC makes it high for three seconds, then makes it go low, which then goes to the “armed” routine. Should the device be powered down during this 3-second period, the high would remain because the capacitor would stay charged. Next time the device is powered up, a high would be present. The microcontroller senses this and it goes into the “disarmed” routine. The 120kΩ resistor and 1N4148 diode control the charging and discharging of the tantalum capacitor. Construction Because of the few components in this project, we’re going to break one of our unwritten rules: as well as presenting it on a PC board, we’re also going to show how to assemble it on Veroboard. Yeah, yeah, we know. We don’t like Semiconductors 1 12C508A pre-programmed microcontroller IC (IC1) 1 MJE3055 NPN power transistor (Q1) 1 78L05 low power 5V regulator (TO-92 package) (REG1) 1 1N4007 silicon power diode (D1) 1 1N4148 silicon signal diode (D2) Capacitors 1 10µF 25VW tantalum electrolytic 2 0.1µF ceramic or polyester Resistors (0.25W, 1%) 1 120kΩ 1 1kΩ it much either because almost invariably, constructors manage to make a mess of it. But in this case, it really is so simple . . . but we’d suggest that if you have your druthers, we’d druther you use the PC board! Which ever you choose, assemble the board in the normal way: lowest profile components first (resistors, diodes, etc), moving on to the capacitors, regulator, switch and finally the IC and power transistor. Note that the power transistor is secured to the Veroboard with a 3mm nut and machine screw – this forms the connection to the siren/ horn “ground” track. Before applying power, check and double check your component placement and orientation – most components are polarised so make sure you Front and rear photos of the assembled PC board. Note the 0.1µF capacitor on the back of the board. This board must be encased in heatshrink (or even mounted in a small box) to protect it from the elements, spray, etc. www.siliconchip.com.au January 2002  55 0.1 120k 1k IC1 D2 1 0.1F D1 10F 1 120Q1 10150 MJE3055 2002 05101021 2002 05101021 2002 HORN + SW1 HEADLIGHT (+) REG1 TOP SIDE OF PC BOARD 1 BATT (+) HORN GND UNDERSIDE OF PC BOARD Component overlays for the top and bottom of the PC board, along with the board pattern itself reproduced same size. get them the right way around. The assembled board (PC or Vero) is “encased” in a length of heatshrink to give some protection from the elements and also to insulate the components from the ’bike. Before you do this, it’s a good idea to check the circuit out and make sure it works! It’s probably easiest to check without installation, by simulating the bike using a 12V battery, a suitable switch and a hefty 12V globe. And you can simulate the alarm sensor with either a pushbutton switch or even a pair of wires to short. Connect them up as per the circuit diagram. Remember when the alarm goes off the siren is going to be very loud. Just warning you! OK, apply power. The voltage between pins 1 and 8 of IC1 should be very close to 5V. If not, check that you actually do have around 12V going in to the regulator. Turn the “ignition” switch off and wait for 30 seconds. Now short the sensor contacts momentarily. You should hear a series of chirps from the siren, followed by silence. About ten seconds after the last chirp, short the sensor contacts again. The siren should now be sounding (we told you it was going to be loud!) and will continue to do so for about 45 seconds. When it stops, short the contacts again and make sure the alarm sounds again. Now you’ll be very pleased to turn the alarm off. Turn the ignition switch on then off again. The siren should go quiet. Thank heavens! Check the disarm feature by repeating the above but when the siren sounds, turn the ignition switch on, off, on, off. The siren should stop and the you should hear a chirp, telling you the system is disarmed. Installation If all is OK, it’s time to seal the circuit board in some heatshrink. The idea is to make it as weatherproof/ waterproof as possible. Seal the open end of the heatshrink with a pair of to be reliable but you don’t want false alarms when, for example, the bike is parked on a hill. As far as the bike wiring is concerned, you only need to make two connections to the bike itself: to the unswitched battery supply and to the power line to the headlight, between the headlight switch and the lamp. Try to add the wiring so that it is as undetectable as possible – you don’t want a crook simply cutting wires. Even though the currents involved The alternative layout on Veroboard. The easist way to cut the tracks is to use a 1/8in drill and twist the point in the appropriate place between the fingers. Practice on a scrap piece first and you’ll get the idea! pliers while it is still hot and place a cable tie on the other (cable) end, again while the heatshrink is still hot. You need to find somewhere safe, out of sight and out of spray, to locate the alarm module. Most sirens also do not like water too much. Each bike is different so we’ll leave that part up to you. Likewise the location of the sensor – choose where it will go carefully. If you are using only a mercury switch, you’ll probably need to experiment a little to get a perfect angle. You want it are fairly small, we have shown heavy-duty automotive figure-8 cable in our photos. This has much better SC insulation than hookup wire.  Wheredyageddit? Preprogrammed 12C508A microprocessor: Available from Mr Mick Gergos, 13 Bunya Street,­Bushland Beach, Qld 4818, for $25.00 plus $5.00 P&P (no longer purchaseable from this address)  Non-position-sensitive motion sensors: Available from Farnell Components (Cat 540-626) or RS Components (Cat 235-7566)  Mercury switches (position sensitive) and piezo sirens:    Available from Jaycar, DSE, Altronics, etc.  Here’s what it should look like once the heatshrink has been shrunk, gripped with pliers (on the left) and fastened with a cable clamp (on the right). 56  Silicon Chip PC boards:   Available from RCS Radio (02) 9738 0330.­­ www.siliconchip.com.au