Transistor Motorcycle Alarm Schematic: Build Your Classic Bike Security

Description

Although intended for operation at 12-volts – this alarm can be readily adapted for a 6-volt system. Therefore, it will safeguard your “Classic Bike”. And since the standby current is zero – it won’t deplete your battery. The circuit incorporates a timed output and an automatic reset. This system can be manually operated using a key-switch or a concealed switch. However, if an external relay is added – it will engage automatically whenever the ignition is switched off.

Any number of normally-open switches can be employed. Ensure the mercury switches are positioned to close when the steering is moved – or when the bicycle is raised off its side-stand – or pushed forward off its center-stand. Micro-switches are ideal for protecting removable panels and the lids of panniers, etc.

While at least one switch remains closed – the siren will activate. Approximately two minutes following the reopening of the switches – the alarm will reset. The exact duration for the system to deactivate depends on the characteristics of the utilized components. However, the time to deactivate can be adjusted to suit your specific needs by modifying the value of C1.

Install the 1-amp in-line fuse as close as possible to your power source. This is VERY IMPORTANT. The fuse serves to protect the wiring – not the circuit board. Both the board and switches must be shielded from the elements. Moisture or condensation will lead to malfunction. Without the terminal blocks – the board is compact. Ideally, you should seek a siren with sufficient internal space to accommodate it.

Instead of a key-switch, a hidden switch or the normally-closed contacts of a small relay can be used. Wire the relay coil so that it's powered while the ignition is active. Then – whenever the ignition is switched off – the alarm will set itself.

When the alarm is activated – if one of the switches is closed – the siren will sound. This could potentially cause disturbance during late hours. A minor alteration will enable you to Monitor The State Of The Switches utilizing LEDs. When the LEDs are all extinguished – the switches are all open – and it’s safe to turn the alarm on.

In standby mode – the circuit consumes virtually no current. This makes it useful in various scenarios. For instance, it can be powered by dry batteries – and with the relay and siren voltages adapted – it could be integrated inside a computer or any other object susceptible to being stolen and carried away. The low standby current and automatic reset mean that for this application – an external on/off switch may not be required.

Schematic Diagram

Veroboard Layout