Car Boot Light Warning


Posted on Feb 5, 2014

On many cars, the boot light will not go out until the lid is properly closed. It is all too easy when unloading the car, to leave the lid ajar. If you are unlucky and the car remains unused for some time, the next time you try to start it, the lamp will have drained the battery and you will no doubt utter a few appropriate words. The circuit described here will give a warning of just such a situation.


Car Boot Light Warning
Click here to download the full size of the above Circuit.

A mercury tilt switch is mounted in the boot so that as the lid is closed, its contacts close before the lid is completely shut. The supply for the circuit comes from the switched 12 V to the boot lamp and through the mercury switch. When the lid is properly closed, the boot lamp will go out and the supply to the circuit will go to zero. If however the lid is left ajar, the lamp will be on and the mercury switch will close the circuit. After 5 seconds, the alarm will start to sound, and unless the lid is shut, it will continue for 1 minute to remind you to close the boot properly. The 1-minute operating period will ensure that the alarm does not sound continuously if you are, for example, transporting bulky items and the boot will not fully close. The circuit consists of a dual CMOS timer type 7556 (the bipolar 556 version is unsuitable for this application). When power is applied to the circuit (i. e. the boot lid is ajar) tantalum capacitors C1 and C2 will ensure that the outputs of the timers are high. After approximately 5 seconds, when the voltage across C2 rises to 2/3 of the supply voltage, timer IC1b will be triggered and its output will go low thereby causing the alarm to sound. Meanwhile the voltage across C1 is rising much more slowly and after approximately 1 minute, it will have reached 2/3 of the supply voltage. IC1a will now trigger and this will reset IC1b. The alarm will be turned off. IC1a will remain in...




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    model train detector using photocell
    AC MAINS LED indicator schematic
    Wide-range-digitally-controlled-variable-gain-amplifier
    Scr Capacitor Turn-Off Circuit
    Battery Watchdog Circuit
    20W Car Audio Amplifier with LM1875
    digital multimeter for your car
    Astable Multivibrator Calculations
    The instrumentation amplifier
    Micropower Dual Single Supply Precision Op Amp
    Time base using a delay circuit touch lamp
    Battery-powered fluorescent lamp circuit 1
    Thermistor basic application circuit b
    INA321 OPA340 composed output buffer circuit 322



    Top