Automobile Lights-On Reminder

The circuit provides a visible or audible warning when the headlights are on. It utilizes a 2N1305 transistor as a switch to activate either a Sonalert tone generator or a small 12-V lamp. The operating current for the transistor is drawn from the wire supplying power to the headlights. When the ignition is on, the transistor remains biased off, preventing the alarm from being activated. However, when the ignition is turned off while the headlights are still on, the alarm is triggered.

The circuit operates by monitoring the state of the vehicle's ignition and headlight system. The 2N1305 transistor functions in a switching mode, where it is normally in the off state when the ignition is active. This is achieved through a biasing arrangement that ensures the transistor does not conduct current, thus keeping the alarm system inactive.

When the ignition is turned off, the biasing condition of the transistor changes, allowing it to conduct. This conduction activates the output device, which can either be a Sonalert tone generator that emits a sound warning or a small 12-V lamp that provides a visual alert. The choice of output device depends on the design requirements and user preference.

The circuit's design is relatively simple, relying on the characteristics of the 2N1305 transistor to effectively switch the alarm system based on the vehicle's ignition state. The integration of a Sonalert or lamp provides flexibility in alerting the driver, ensuring that they are aware of the headlights being left on, which could otherwise lead to battery drain.

Overall, this circuit serves as a practical solution for enhancing vehicle safety by preventing unintended battery depletion due to the headlights being left on after the ignition has been turned off. The circuit can be used to give a visible or an audible warning that the headlights are on. It uses a 2N1305 transistor as a switch to turn on a Sonalert tone generator or a small 12-V lamp. Operating current for the transistor is supplied from the wire that feeds the headlights. When the ignition is on, the transistor is biased off and the alarm is not activated. Turning off the ignition while the lights are on sets off the alarm.