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Motorcycle anti-theft device. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automobile. Security devices and alarms

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The proposed anti-theft device does not contain a hidden switch. In standby mode, the device does not consume electricity, which is especially important for small battery capacities. The design is original in that it is placed inside the Java motorcycle headlight, but it can also be used in other types of motorcycles and cars. In this case, it is imperative to take into account the polarity of the power supply of the on-board network.

Schematic diagram of the first version of the device is shown in Fig.1. The low supply voltage (6 V) led to the use of a signal switching relay switch, since the voltage drop across the key transistor or thyristor significantly reduces the volume of the signal.

Motorcycle anti-theft device

With the contacts of the limit switches SB1 and SB2 open and the ignition off, the polarized relay K1 is in a state where the contacts I-P are open. Relay K2 and horn de-energized.

During the operation of the motorcycle, it turned out that any person who approached the motorcycle with good or evil intention immediately takes the wheel and turns it into a comfortable position. This property is the basis for the operation of the anti-theft device. Switches SB1 and SB2 are installed inside the headlamp and therefore do not attract attention. SB2 is installed so that at the extreme right position of the motorcycle steering wheel, its contacts are open.

When the steering wheel is turned to the left, the contacts close, relay K1 turns on through the capacitor C1, the P-I contacts close, relay K2 turns on, which turns on the sound signal with its contacts. When the ignition is turned on through resistor R2, voltage is applied to relay K1, the contacts P-I of relay K1 open, and the sound signal stops. It should be remembered that the ignition locks in such motorcycles are numbered and the selection of a key in the field is almost impossible. You can block the SB1 switch by climbing inside the headlight, but the SB1 switch is installed so that it is impossible to remove the headlight (it works when you try to remove the headlight).

But even at the same time, there remains one more opportunity to neutralize the alarm by connecting an external battery to the terminals of the ignition coils, which are located under the fuel tank and have free access. To exclude this possibility, a VD1 diode is installed. This diode should have a minimum forward voltage drop at a current of up to 5 A. The fact is that the installation of this diode has some undesirable consequences: it is difficult to start the engine with a heavily discharged battery and it is difficult to drive at low engine speeds of the Java motorcycle at night with the headlight turned on due to the insufficient power of the onboard generator.But these are non-standard situations, and this should be taken calmly (the remark applies only to Java motorcycles).

Depending on the position in which the steering wheel is left, the circuit is in the off or on standby state. In the off mode (steering wheel to the left), the capacitor C1 remains charged, and when the contacts SB2 are opened (closed), relay K1 is not transferred. If you leave the steering wheel in the extreme right position, then the contacts SB2 will open, and the capacitor C1 will be discharged through the resistor R1. The ratings of C1 and R1 are selected in such a way that the discharge time is 20-30 s.

The owner must turn on the ignition without turning the steering wheel. It does not attract the attention of others by some additional actions. If the driver coasts for a long time with the ignition off (by the way, this mode is very harmful for two-stroke engines due to the cessation of lubrication of the piston groups), then the alarm will still not work, since the contacts SB2 cannot be open for a long time, and the capacitor C1 does not manages to unload.

However, the circuit turned out to be not very practical: when the security device is triggered and the owner is absent for a long time, the sound signal “burns out” (with a good battery). To prevent this from happening, the device was first supplemented with a multivibrator, and then a time relay.

The modified scheme is shown in Fig.2. The circuit provides 3-4 beeps and turns off.

Motorcycle anti-theft device
(click to enlarge)

As a polarized relay, it is imperative to use relay switches with two control windings, for example, RPS20, RPS28, RPS32, RPS34, RPS36, RPS42, RPS43, RPS45, RPS47 (suitable for voltage). It is possible to adjust a neutral polarized relay for this mode, but not all of them can be adjusted, and the adjustment itself requires some experience. When installing such a relay on a motorcycle, be sure to pay attention to the fact that the anchor moves horizontally, otherwise, with strong shaking, the relay may spontaneously be thrown.

Any relay with powerful contacts and a suitable voltage can be used as an intermediate, but relays of the TK type are best suited for this purpose.

As a multivibrator, you can use a ready-made IZH motorcycle turn relay by doubling the capacitances of capacitors C3 and C4.

The reaction of people to the operation of such an alarm is curious. At first, out of surprise, a person shudders and moves away, but then he tries to do something, including turning the steering wheel. At this point, the signaling stops (the delay time has elapsed). Having pulled for everything that is possible, the person leaves. But curiosity pulls back, and after a while he returns. The alarm goes off again. For a long time, my friends were sure that this was a capacitive relay, but everything is much simpler.

When installing such a device on a car and using the reversing light switch as a sensor, the following happens: they kicked the wheel with their foot - it is silent, they opened the doors - it is silent. The thief calms down. But before turning on the ignition, towing, trying to roll away, the hijacker is forced to set the gear lever to neutral. This is where the alarm goes off.

For the automotive version, you need to slightly modify the switching circuit, but this is within the power of a radio amateur with little experience. Moreover, as SB1, you can use the engine hood sensor.

I used a mechanical “limit switch” as the SB2 limit switch. It has been working for me for 28 years! But sometimes after the winter it has to be trained several times. By using a reed switch, you can avoid this inconvenience.

Please note: even if you are followed, it is almost impossible to notice that you have turned on the alarm.

Author: V.M. Paley, Chernihiv

See other articles Section Automobile. Security devices and alarms.

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