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  • Ultra simple circuit of the tilt sensor alarm presented here can be fabricated using readily available inexpensive components. The circuit is a true transistor based design. Home made Tilt sensor for this circuit is an ordinary little glass/plastic bottle with two metal needles inserted through its cap, and a small quantity of water inside.
    You can also try your own ideas to make the tilt sensor. A 9V alkaline battery is enough for powering the whole circuit.

    Tilt Sensor Circuit Schematic

    tilt sensor alarm schematic

    Usually, transistor T1 is in inactive state. When the sensor assembly is tilted, both needles inside the sensor (bottle) are short circuited by the water and a positive voltage is available at the base of T1 and it becomes active. Activation of T1 causes the activation of next transistors T2 and T3. After this, T2 supplies constant bias for T1 to make it latched and T3 triggers the SCR(T4) which inturn energises the active piezo-sounder(BZ1). Once activated the circuit can be deactivated by depressing the power/reset switch S1.

    Preset pot P1 is deliberately added here to adjust the circuit sensitivity. This may become necessary if you are trying a different (readymade) tilt sensor. Similarly,SCR(T4) and piezosounder (BZ1) may be replaced with near equivalent parts. Resistor R3 (100-150 Ohm) is optional.

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    4 Responses to "Tilt Sensor Alarm Circuit"

    1. This circuit just needs a mercury switch or “ball switch”

    2. Thanks to Mr. Colin Mitchell for his feedback. My prototype was tested with this home-brewed “tilt switch”. But it is always better to use a ready-made tilt switch.

    3. A limiting resistor(4.7kΩ minimum) must be tied in series with the tilt sensor, otherwise +9V is applied in the base of T1. Needless to say that T1 will blow up in case of using a mercury or a ball switch tilt sensor, for example.

      Likewise, a limiting resistor(>1kΩ) in the emiter of T2 won’t hurt.

      Anyway, you can get the same results with only one transistor and the SCR(BT169). This schematic is useless complicated.

    4. Clive Grant says: on March 3, 2014 at 2:01 pm

      Yes, a resistor is required in T1 base supply to drop the power supply voltage. Otherwise, catastrophic failure of T1. It looks as if the circuit diagram has been drawn by a 7 year old novice.

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