help in RADAR

Discussion in 'The Projects Forum' started by shankbond, Jan 7, 2008.

  1. shankbond

    Thread Starter Active Member

    Nov 4, 2007
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    hi,to all of you
    I m shankbond ,currently i m doing my engineering in final year,i have to submit a project which i have choosed as a RADAR.

    i m making a radar by using an infrared transceiver which i m somehow making to go rotatory i will interface this antenna with a microcontroller which will interface(controlling the speed of rotation) with this antenna as well as with PC(sending the speed of rotation and the angle of detection).
    the problem is:

    1> how should i connect a rotating antenna with a stationary microcontroller,initially i have chosen a brush contact with slip ring just as in an in a electric motor(but that is just a theoretical concept,any possible 'practical' alternative will be highly appreciated)

    2> the second problem is how should i interface my microcontroller with a personal computer,like i have thought of using a RS-232 cable but that is the hardware level interfacing ,how to create a software level interfacing in C or C++,which functions to be used.


    thank you
    any help on the aforesaid problems will be highly appreciated.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Since you've chosen to use an IR transceiver, you will be creating an optical infrared device, not a RADAR (RAdio Detection And Ranging).

    If you have already told your professor that you were considering building a RADAR for a final project, I suggest that you inform him you changed to IR due to safety considerations. Otherwise, he will likely deduct a significant amount off of your grade.

    Instead of allowing your antenna to rotate 360°, consider limiting it's travel to 120° or 180°, and oscillate the antenna back and fourth. This will enable you to use ribbon cable as an interconnect, instead of having to use slip rings. Such limited travel is typical of tactical radar and IR tracking devices.

    To move your antenna in the X axis, you'll need either a fairly powerful stepper motor, or a servomotor. You will also need to provide feedback with a rotational encoder or similar device, so that your uC knows for certain the current position of the antenna.

    You're also going to need to automatically scan the antenna in the Y axis, as well as allowing manual input to adjust the elevation (if desired). So, you'll also need a stepper motor or servomotor and rotational encoder or similar for that axis. As before, if you limit your Y axis travel, you can use ribbon cable as interface.

    As far as getting data to a computer, RS232 will be extremely slow, and won't be capable of handling the amount of data your IR device will be able to send. If you're using Windows, consider using a USB or Ethernet interface instead.

    You have another problem involving range information. In an old-fashioned radar, a short pulse (about 0.63 uS) of RF is sent out, and the time it takes to return is the distance from the object. It takes 12.6 uS for the RF energy to make a 1-mile round trip. It's going to be roughly the same for your IR project, but switching your IR illuminator on and off that quickly is going to be problematic. You will need to account for the propagation delays through each item in your IR system. When your IR illuminator is on, it's likely that your IR receiver will be "blinded" by them until they are turned off. This makes it difficult to acquire ranging information at short distances, unless there is enough separation between illuminator and receiver. In the case of this particular radar, the minimum detectable range is 300 feet.

    The range of your IR device will be limited by not only the strength of your illuminator and the sensitivity of your receiver, but by the pulsewidth firing your illuminator and the PRF of that pulsewidth. The precision and reflectivity of your reflector dish will figure in heavily in sensitivity.

    However, you could still use it as a passive IR device (receive only, no illumination). You will not receive range information in passive mode, but if your receiver is sensitive and directional enough, you may be able to discriminate between relatively hot/cold objects.
     
  3. Gadget

    Distinguished Member

    Jan 10, 2006
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    Sonar might be another option if you want short range.
     
  4. hgmjr

    Moderator

    Jan 28, 2005
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    What is the maximum detection range you are trying to achieve with your IR range finder?

    Instead of using a DC brush motor, you may want to consider using a stepper motor. With a stepper motor you will have a bit more control over the position and rotation speed of your antenna.

    hgmjr
     
  5. shankbond

    Thread Starter Active Member

    Nov 4, 2007
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    0
    First of all i m very thank full to the people of this forum who are constantly giving suggestions and helping people like me to gain some information ,it is they who have the practical knowledge and they share with us ;and because of their best efforts i and other people get a great help from them.



    well, very thanks ,i and my friends choosed this because it was cheap:)

    thanks again for ur advice ,and we have done that too:)

    i m sorry i didn't get ur point, could you please further elaborate it.
    well, we are using a stepper motor for the purpose of rotation and we will just simply put the transciever sticking to motor.so, i believe that theoretical there should be no problem in rotating the device 360 degrees and knowing the angle of rotation and speed of motor, the only problem is how to transfer the detected signal to microcontroller.

    well thanks for the advice, we will now focus on the problem ,and will rectify it.
     
  6. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    Using unwired communications opens a 'can of worms' as far as implementation. You then need to worry about powering the transciever via batteries, or a simpler slip-ring structure as compared to signaling. Then, you need to worry about encoding data, error checking, etc.

    Steve
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    My point is, that if you don't rotate the antenna around and around in a circle, and instead wave it back and fourth (oscillate), you can use a flexible ribbon cable for your signals instead of having to resort to multiple slip rings. Turning the antenna 360° is easy. Getting the signals from the antenna to the uC when it's constantly spinning is not. Waving (oscillating) the antenna back and fourth 120° or 180° is a little bit more difficult than spinning it 360°, but it makes interfacing the signals very simple by using a flexible ribbon cable.

    The difficult part will be slowing the antenna down (deacceleration or braking) near the end of it's arc, reversing it's direction and accelerating it back to the desired scan speed in the opposite direction. You must stay within the liimits of your stepper motor's torque capabilities to accelerate/deaccelerate the mass of the antenna. However, you would need that kind of routine anyway to properly accelerate the antenna to scan speed, even for the 360° scan.
     
  8. hgmjr

    Moderator

    Jan 28, 2005
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    How about putting a microcontroller on the platform containing the IR transceiver/receiver. The micro could then be used to manage the IR system, the motor positional system and the serial communication up-link and down-link.

    The communication could consist of a small short range 915 MHz transmitter to send data from the moving platform to the stationary platform (the PC). This traffic would be the information from the IR system as well as positional data. Commands and data requests could be handled using a short range 433 MHz data link from the PC to the micro located on the moving platform. This would segregate the data traffic into two seperate RF channels.

    DC Power to the moving platform would be handled via the slip rings arrangement that you have already mentioned. I neglected to mention that the motor would be inverted. That is the shaft of the motor would be attached to a fixed base and the electronics would be mounted to the body of the motor.

    Just spit-balling here.

    hgmjr
     
  9. shankbond

    Thread Starter Active Member

    Nov 4, 2007
    53
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    now i got your point,but again a question?
    if i can rotate it 180 degrees ,why not rotate it 360 degrees and bring ti in reverse direction:confused:

    thanks for telling me this important information regarding torque,i never thought of it.:)
     
  10. shankbond

    Thread Starter Active Member

    Nov 4, 2007
    53
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    i initially thought of it too; but don't u think that the motor would get an additional load on it and also the project will get more costly too.and would cause an ultimate burning of it.


    this concept is also great but the problem is i m a purely theoretical at the moment ,so i dont know if i could get a slip ring made(ready to use) in the market and would weld it with the motor?
     
  11. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    You comments are not surprising. I do understand all too well how budgetary constraints have a strong influence on what can be undertaken. I wasn't sure how much you were willing to take on in terms of cost and complexity so I threw it out there to see if it was a fit or not.

    Sgtwookie's suggestion of wig-wagging the IR transmitter/receiver sounds like your best bet at simplifying the scanning function.

    I will follow this thread in the coming days/weeks to see it there is anything else I can do to assist you with your efforts.

    Good Luck,
    hgmjr
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Indeed, you COULD scan the antenna 360°, reversing at each end of travel. That will require careful routing of the cable(s) in a clockwork-spring fashion to reduce the strain, wear and tear on them.

    Inverting the stepper motor is an interesting idea, but that would likely add a considerable amount of mass to the antenna, requiring more torque to start/reverse it's direction. Adding a couple of transcievers for command and signal datalinks would significantly increase the complexity of the project. Each of these items would require additional power, whether it be supplied externally via slip rings or by batteries, which seem to be growing larger by the moment due to increased power requirements; the larger batteries require more torque - I think we're about to get stuck in a loop here. ;)

    Besides reducing interface complexity, limiting the antenna scan to 120° has the advantage of tripling the sample rate for a given antenna scan velocity. For example, if you were planning on scanning the antenna in a 360° circle, completing one revolution each 3 seconds - you could scan 120° three times in that 3 seconds (with some overhead time for braking/reversing direction of course.) Lots of things can happen (move, change intensity) in three seconds, particularly at close ranges.
     
  13. shankbond

    Thread Starter Active Member

    Nov 4, 2007
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    i believe that is sufficient information for now,hope that all things go well when we are assembling the project:):cool:



    and as well as help is concerned (if i will need any help) i will continue in this thread (this will help keep track of all the previous conversations:cool::rolleyes:)
    )

    thanks
     
  14. shankbond

    Thread Starter Active Member

    Nov 4, 2007
    53
    0
    all most forgot about interfacing:)

    could u guys give any reference sites or material regarding the software part of interfacing of microcontroller with computer?
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Interfacing a microcontroller to a computer will greatly depend upon the uC you choose. There are myriad protocols in use.

    You need to first decide how you're going to handle the incoming stream of information from the IR receiver. Are you going to keep it analog, or are you going to use an ADC to convert it to a digital stream? If you're converting it to digital, what degree of precision are you going to use; 7-bit, 8-bit, 10-bit, 12-bit, more? The addition of each bit of resolution increases the accuracy, but also increases the complexity of the circuit, conversion time, and the amount of data to be transmitted.

    Simple protocols like 1wire or old protocols like RS232 won't be suitable, because there is simply not enough bandwidth available.

    If you are going to be using passive mode only (no transmit), there will be considerably less data to deal with.

    You're also going to have to decide on an architecture for your data stream. Simply throwing raw data at your computer won't do much good; it needs to have other information in there, such as the azmuth and (optionally) elevation of the antenna, if you're in active mode you'll also need to timestamp the data for range information.

    Here's a tidbit for you: a pulse of 8.547 nanoseconds translates to a range resolution of 10 meters. This requires a clock frequency of 117 MHz.
     
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