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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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    29 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. 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.

    5. As a matter of fact there are some parts completely useless in this schematic.

      This circuit(Tilt Sensor Alarm) could be made fully functional using only the thyristor, a gate current limiting resistor and the 100nF capacitor. All the rest are useless and moreover T1 and T2 will blow up(at least will drain the battery for sure!!!) because there is no base-emitter-collector limiting resistor.

      Also, the 100Ω resistor will drain the battery in no time. This resistor should be at least 1.2kΩ in order to mantain the holding current(max 6mA).

      This schematic is hilarious. The author wasn’t aware of what he was doing.

    6. Colin Mitchell says: on July 22, 2015 at 1:15 am

      T.K. Hareendran has no idea how to produce electronic circuits. Do not build this circuit.

    7. Any one can come up with ideas. But the implementation is very difficult, that is why many self-proclaimed electronics gurus just posted cheap comments and disappeared. Why they failed to publish their own improved circuits here? “typing culture less comments is easier than building a working circuit”. All of them including Colin knows this well!

      Here the base resistor is not very important because the sensor is a sealed one.

    8. Colin Mitchell says: on July 27, 2015 at 6:36 pm

      Nishima – you don’t know what you are talking about.

      The circuit DOES NOT WORK. The first transistor will blow up as soon as the tilt sensor is moved.

    9. Tested the circuit exactly as shown in the article with water filled in my homemade tilt sensor (small bottle with needles). Working well, and no fumes.

      Electronics is more of an Art than a Science. Use trial and error and explore what will happen if …..

    10. Colin Mitchell says: on July 28, 2015 at 8:14 pm

      Touch the two terminals together and let me know what happens

      • T.K.Hareendran says: on July 29, 2015 at 4:21 am

        Who can touch the needles inside a sealed bottle? Your intention is just to publish irrelevant (and dirty) comments here (in your name, and using other “fake” names) to attract visitors to your website!

    11. Colin Mitchell says: on July 29, 2015 at 4:53 am

      That’s only the first problem. Of course you should have protection if the probes touch.
      T1 and T2 have no current-limiting resistor.

    12. T.K.Hareendran says: on July 29, 2015 at 5:30 am

      @Colin Mitchell:

      Please keep your language clean. I am not a circuit designer receiving remuneration from you. Reserve your cheap replies for those working with you,if any.


      The one and only magazine publishing Colin’s 70’s- model circuits is Electronics Maker (published from India, not from Australia). Since the magazine pays nothing for contributors,they can play with the poor stuff. His bundled-submission has been rejected by EFY magazine only because of its “standard” (I’ve solid evidence in this matter,and ready to publish if requested). I know the reason why all Indian, Australian & UK magazines closed their doors and throw off this old demon!

      @ Site Owner:

      I request the site owner to cast off guys like Colin Mitchel from posting irrelevant (and biased) comments here. I consider this precious space as a platform for talking & learning about electronics. Do not promote others cheap business trickery!

    13. Colin Mitchell says: on July 29, 2015 at 10:14 am

      Go to my website TALKING ELECTRONICS and you will see pages of faulty circuits designed by T.K.Hareendran. He doesn’t have a clue about designing a circuit.

      ” I consider this precious space as a platform for talking & learning about electronics.”

      And learning about HOW NOT TO DESIGN A CIRCUIT !!!!!!

      Touch the two terminals together and let me know what happens
      Are you mad? Who can touch the needles inside a sealed bottle?
      In your instructions you say:When the sensor assembly is tilted, both needles inside the sensor (bottle) are short circuited by the water

      YOU are the one that mentioned SHORT-CIRCUIT!

    14. Colin Mitchell says: on July 29, 2015 at 1:23 pm

      Let me explain why this is the worst circuit on the internet. Not only has it been designed by
      T.K.HAREENDRAN who states he is a “professional electronics engineer” with many circuits in many magazines, but it will blow up the transistors.

      The circuit starts by connecting the battery and the 100n prevents voltage appearing on the base of the base of the first transistor.
      This means the first transistor is not turned ON and both T2 and T3 are not turned ON.
      When the tilt sensor allows current to flow into the base of the first transistor, it is turned ON
      The tilt sensor will only turn it on a small amount and will not damage the transistor.
      But as the transistor turns ON, a voltage develops across the 10k resistor and this allows T2 to start to turn ON.
      It turns ON with a small amount of current into the base but 100 times more current flows in the collector-emitter leads and this current begins to turn on T1.
      T1 now receives 100 times more base current and this action continues until both transistors are fully turned ON.
      There is no current limiting resistor in the circuit and both transistors WILL BLOW UP.
      At the same time T3 is turned on FULLY and it has no current-limiting resistor and it will BLOW UP TOO.
      This makes it with worst circuit on the web.

    15. How do you analyze the SCR for this circuit???

    16. Colin Mitchell says: on July 29, 2015 at 8:14 pm

      “How do you analyze the SCR for this circuit???”

      Why do you want 90mA to energise the gate of the SCR?
      The 100 ohm resistor is far too low.
      What is the purpose of R3 ????
      The whole circuit is just JUNK,
      T.K.HAREENDRAN cannot design for nuts.
      Why have a latching circuit in the front-end when the SCR is a latch???

    17. Colin Mitchell says: on July 29, 2015 at 8:39 pm

      T.K.HAREENDRAN obviously used a weak 9v battery to test the circuit and that’s why he thinks it will work.
      Try a 9v power supply or increase the voltage to12v and see SMOKE.
      T.K.HAREENDRAN keeps sending me rude emails under a different name but never explains where he got his bazaar education or why he keeps outputting such JUNK.
      I get hundreds of emails from around the world from readers who have said my website has taught them more than all the education from their university studies.
      These are not my emails. These are from readers and I include their email address.
      Show me anywhere where my comments are irrelevant or biased?
      I criticise ANYONE who delivers faulty circuits.
      I have 25 pages of faulty circuits and this is hundreds of circuits.
      Not one person has written to say any of my comments are incorrect.
      There is not one other person on the web that has produced such a library of faulty circuits and an analysis of how and why they are faulty.
      You can learn more from these pages than any text book.
      It is T.K.HAREENDRAN and authors like him that should be stopped from putting such junk on the web.
      His circuits are just giving electronics a bad name.
      Beginners will be hesitant to build anything when they find the circuits either do not work or just BLOW UP THE TRANSISTORS.

      • our comment is awaiting moderation.

        Right on!

        Either this guy doesn’t know how a SCR works or he doesn’t know what a latch is. That’s sad.

        On the other hand…

        I’ve been watching the polemic between you and T.K.HAREENDRAN and it seems it will never end. I think it’s time to put an end to this. Let him be. Don’t be too harsh on him. I think he’s got it.

    18. Colin Mitchell says: on July 30, 2015 at 12:40 pm

      “I’ve been watching the polemic between you and T.K.HAREENDRAN and it seems it will never end. I think it’s time to put an end to this. Let him be.”
      An intelligent person would make corrections to the project so others don’t build something that does not work.
      You will notice he does not even rely to my corrections.
      I have pages and pages of his faulty designs and he keeps putting this stuff in Electronics For You Magazine, where the editor has absolutely no understanding of electronics and just publishes this rubbish.
      And an intelligent magazine would publish my corrections – but they hide behind not ever answering any of my emails.
      What more can I say.

    19. Colin Mitchell says: on July 31, 2015 at 7:57 pm

      Instead of answering my comments about the poor circuit design, T.K.HAREENDRAN sends me this stupid email:

      After doing some research I found that you are a big zero that knows nothing in advanced electronics. What you can do is wiring circuits using bc series transistors and old pics. The resulting irritation is the real fact behind your madness-driven criticism.

      You are a critic without any updated credentials to show before the public. You are just repeating your old stories.

      Your victims like dattatajvidyasagar,dmohnakumar, all are reputed indian geeks with years long experience in the domain. I am not a keralite but I maintain a good relationship with all of them since my iit days. tk sir maintains a well-established lab, dmohnakumar runs a good project centre,dattaraj sir just started a new academy. I salute such persons.

      But when turning to you, you are a mad guy needs adult supervision and medication. If I can I will throw you off from web to stop the ever-increasing polluting activities by you.TALKING ELECTRONICS: WHAT IS IN IT? NOTHING TO FOLLOW %%%FU

      You can see the dozens of faulty designs of all these “geeks” on my website.
      None of them know the basics of electronics and none of them have challenged any of my comments.
      Simply build any of the circuits designed by these “geeks” and you will see the faults.
      TK SIR had a terrible website until I exposed his lack of knowledge and his site was taken down. All the faulty circuits were removed !!!
      You can still see all his rubbish on my website.

      I have dozens of faulty circuits from T.K.HAREENDRAN.
      All I am doing is exposing ANYONE who produces the wrong information ON ANY SUBJECT.
      I have never had any comment from anyone to say my comments are incorrect.
      I have had 22million visitors to my website and T.K.HAREENDRAN is the only one that sends stupid emails without ever acknowledging his mistakes.
      I ask him to comment on why he has produced such a stupid circuit TILT SENSOR and why all his circuits have faults.

    20. T.K.Hareendran says: on July 31, 2015 at 8:09 pm

      Now I think Colin Mitchel have some madness. Because I have no idea about the above posted email. Who sent it?

      Further, I haven’t a website till date. I wonder what he mention about. I think this is another trickery by him.

      This is my final response to Colin’s comments because he deserves nothing, and time is valuable!

    21. Oh my God not again!

    22. Colin Mitchell says: on August 4, 2015 at 2:07 pm

      “This is my final response to Colin’s comments because he deserves nothing, and time is valuable!”

      Why doesn’t T.K.HAREENDRAN answer my comments as to why he did not included current-limiting resistors in the circuit ????

      He just keeps sending me rude, inconsequential emails, without answering any of the points I have brought up about his faulty designs.

      It’s no wonder beginners get put-off with the internet, when inept people are allowed to present circuits that have never been tested and are not updated when shown to be faulty.

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