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Reverse polarities by a device

  1. Dec 31, 2009 #1
    There is nothing I have tell before I go about on this madcap search. The problem is that I'm only 12 and searching for a device (or a circuit) which changes, or swaps, polarities, every time the switch (a switch made from a phototransistor and a resistor, in essence, getting activated wirelessly) is on. In other words, the motor (brushed) to which it will be connected will spin in one direction, and will begin to spin in the opposite direction once the switch is switched on.
  2. jcsd
  3. Dec 31, 2009 #2
    You need 2 things: a flip-flop circuit, and a reversing circuit. Your trigger (the phototransistor) will change the state of the flip-flop with each activation. The flip-flop should activate the coil of a DPDT relay wired as a reversing switch.
  4. Dec 31, 2009 #3


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    If you click on this diagram, it will get bigger:

    Reversing switch.PNG

    It is a reversing switch.
    Those switches at the sides of the motor can be operated by a relay or they can be real switches that are operated by one knob.

    Notice the two possible positions of the switches. Doing this reverses the direction of current flowing in the motor. With some motors, this will reverse the direction of the motor.

    The red lines are there to show the direction of the current flow in the black wires.
  5. Dec 31, 2009 #4
    Thanks. New year wishes, my friend! But just help me know how I make a flip-flop switch with a phototransistor as aforementioned, for I would prefer it if zgozvrm would send me a schematic diagram explaining the circuit he he has suggested.
  6. Dec 31, 2009 #5


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    You don't need a FF if the signal out of your phototransistor is always valid. FFs are used for 1-bit memory storage.

    Here's a wiki page on H-bridges that vk6kro showed you. You should be able to use your optotransistor output and a couple of gates/inverters to make the signals to drive the 4 switch transistors.


  7. Dec 31, 2009 #6
    See this site for information on how flip-flops work:

    I would suggest using the T-Type flip-flop with the T input constantly set high. Then use the clock input as the trigger (the output of your phototransistor). Each time the phototransistor triggers, the T flip-flop's output would toggle. This, in turn, could drive an output transistor that could drive the coil of a DPDT relay wired as a reversing switch (as vk6kro's diagram shows).

    There are, of course, many other ways to accomplish the same thing. This is just the first thing that came to mind for me.
  8. Jan 1, 2010 #7
    If you see the attachment, you will know that I have formulated the circuit of reversing poles using a DPDT switch. There is a part enclosed in a dotted blue box, the DPDT, which I have marked so that it can be removed and replaced with a diagram on a DPDT using phototransistors.

    Attached Files:

  9. Jan 1, 2010 #8


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    Your circuit will probably work, but it uses two batteries.

    It is better to use just one battery and some clever switching to reverse the polarity.

    I have tried to make this one a bit clearer.
    Reversing switch 3.PNG

    Can you see that the current through the motor changes direction, so the motor reverses?

    Here is the same thing drawn a different way.
    Reversing switch 2.PNG

    In each case, the switches are joined together so they operate at the same time.
  10. Jan 1, 2010 #9
    I have redesigned my model as below, based on your suggestions. You may ask, why three batteries? In fact, one battery in this circuit provides 9 volts, i.e. a 9v battery, so three batteries gives me an output three times as great.

    By the way, I did forget to ask, how I make a DPDT switch using phototransistor pairs modulated to different frequencies. I need your help to find the requirements I need, that is, two pairs of IR LEDs and phototransistors, each pair of LED and transistor modulated to different frequencies. No, don't ask me why, they don't sell PTs nor LEDs anywhere nearby, and googling proves to be futile.

    I have to tell you what exactly I have in mind. A zeppelin, lifted by helium gas balloons. The only problem that remains apart from the motor being activated wirelessly (I know, I'll make sure I add some ballast so that it is no more that at a maximum 7 feet high, so that I have contact range with my zeppelin and don't have to use RC control) is to make a system that moves the rudder and the ailerons (with phototransistors, of course).

    And lastly, is there any way I can be posted a diagram on how to make a RC system instead of IR, along with the requirements?
  11. Jan 1, 2010 #10


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    There was no diagram on your last posting.

    However, you seem to be a bit over-ambitious. I know the exciting stuff is more fun, but you need to get used to the basics first.

    I can assure you that radio control would be much more suitable for a Zeppelin than infra red control which only has a range of 30 ft or so if you are lucky.
  12. Jan 2, 2010 #11
    Hi vk6kro. There was indeed no attachment, in fact it was just nearly the same thing you showed me in the previous post.

    In that case, could you provide me with diagrams illustrating the receiver and transmitter end of the RC control?
  13. Jan 2, 2010 #12


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    In that case, could you provide me with diagrams illustrating the receiver and transmitter end of the RC control?

    No, I don't think so. You can hunt around on Internet or rip a cheap remote controlled toy apart if you like. These are incredibly cheap and often very good quality.

    Good luck with it.
  14. Jan 2, 2010 #13
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