RF transmitter - RF receiver project

Discussion in 'Wireless & RF Design' started by Cris909, May 5, 2014.

  1. Cris909

    Thread Starter New Member

    May 4, 2014
    28
    1
    Hello,

    I am looking for information on a project I'm creating for school.
    I need to create a small RF transmitter that sends a unique transmission around a radius of 500 feet. Then I need to create a receiver that can receive that unique signal and simply cause it to light a button on the receiver signaling it is receiving that transmission when it's within the 500ft range. Any information at all will help.

    Thank you,
    Cris Garcia
     
  2. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    I would just send a radio signal with no modulation to make it simple. This could just be a pulse train from an op amp at, say, 300kHz. Then I'd make a receiver with a common emitter amplifier driving a detector. With the dc voltage from that I'd switch on an LED.
     
  3. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    After thinking about it the simplest approach would be to use an op amp configured as an oscillator at an rf frequency, say 300kHz and have it drive an antenna which would consist of just a long wire. That's your transmitter. The receiver would be fed by another long-wire antenna and drive another op amp, this one configured as either an inverting or noninverting amplifier with its output feeding an LED in series with a small resistor.

    That's the simplest approach. If you need more power have the op amp transmitter feed a common emitter amplifier which in turn feeds the antenna. Try different antenna lengths. The wire can be small magnetic wire.

    If this doesn't satisfy the criteria then you'll have to elaborate on what a unique signal is.
     
    Last edited: May 6, 2014
    Cris909 likes this.
  4. Cris909

    Thread Starter New Member

    May 4, 2014
    28
    1
    This project is new to me so everything you have said so far I will be researching so I know exactly what your talking about and exactly what I need to buy.
    I am trying to mimic a beacon signal.
    Would a dorji receiver/ transmitter be a place to start?

    I appreciate all your help, your the only one that has any idea of what I'm trying to do!
     
  5. Cris909

    Thread Starter New Member

    May 4, 2014
    28
    1
    Also how would I go about getting or making an op amp oscillator at an rf frequency?
     
  6. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    There are many op amp oscillator diagrams out there on the web, just google the question and pick a simple configuration. As for having it behave like a beacon, you'll need to time the transmitter such that it turns on and off every second or so. This would involve a second oscillator enabling the first and pulsed at one second intervals. In this case, rather than the op amp transmitter use a 566 timer, which is an eight pin IC which includes two 555 timers. The first one runs at one second pulses to enable the second at 300 kHz. The receiver is the same as described above.

    If you want to increase the range of radio transmission, you can have it drive a BJT amplifier which feeds the antenna.
     
    Last edited: May 12, 2014
    Cris909 likes this.
  7. Cris909

    Thread Starter New Member

    May 4, 2014
    28
    1
    I see, it seems like there is many ways to go about what I'm trying to do. I appreciate your help I will be doing more research on what you have said today.

    Another member gave me some advice, I would like to know what you think about it. It's as follows..

    Not much info so most of this is based on a few guesses I made.
    http://www.silabs.com/products/wirel...s/default.aspx

    What I would do Pick a wireless transmitter MCU and receiver MCU from the above link, the reason is I have used there stuff alot lately and its good, the wireless mcu's are good energy wise, that makes it possible to use energy harvesting and small battery for power system, you get full control over the transmitter frequency and channel, they have a software system that makes setting the whole thing up easy.You can define the payload and number of data packets etc, you can set up encryption easy. You didnt mention if its a continuous beacon or if you are going to say have it transmit every x seconds/mins, I would do every x seconds, this means if you choose the right energy harvesting system and use some super caps, you could probably get away without a battery on the transmitter, as you have full control on output power, then getting 1000' wont be too hard, it wont be exact though.One big advantage with sil labs is the software they give away free, you can use it to test range and signal strength etc, I have used there radio kits alot lately and found them easy to use and set up, they have been very energy efficient.I would be tempted to just by the EZ radio dev kit and use that, then you can walk around with the receiver and get the figures you need (signal strength etc) in order to set up the transmitter properly.If you think it will do what you want, then give me a shout. I have some of the dev kits here and would be willing to try a few things out for you, as long as I am not having my op of course
     
    PRS likes this.
  8. Cris909

    Thread Starter New Member

    May 4, 2014
    28
    1
    I see, it seems like there is many ways to go about what I'm trying to do. I appreciate your help I will be doing more research on what you have said today.

    Another member gave me some advice, I would like to know what you think about it. It's as follows..

    Not much info so most of this is based on a few guesses I made.
    http://www.silabs.com/products/wirel...s/default.aspx

    What I would do Pick a wireless transmitter MCU and receiver MCU from the above link, the reason is I have used there stuff alot lately and its good, the wireless mcu's are good energy wise, that makes it possible to use energy harvesting and small battery for power system, you get full control over the transmitter frequency and channel, they have a software system that makes setting the whole thing up easy.You can define the payload and number of data packets etc, you can set up encryption easy. You didnt mention if its a continuous beacon or if you are going to say have it transmit every x seconds/mins, I would do every x seconds, this means if you choose the right energy harvesting system and use some super caps, you could probably get away without a battery on the transmitter, as you have full control on output power, then getting 1000' wont be too hard, it wont be exact though.One big advantage with sil labs is the software they give away free, you can use it to test range and signal strength etc, I have used there radio kits alot lately and found them easy to use and set up, they have been very energy efficient.I would be tempted to just by the EZ radio dev kit and use that, then you can walk around with the receiver and get the figures you need (signal strength etc) in order to set up the transmitter properly.If you think it will do what you want, then give me a shout. I have some of the dev kits here and would be willing to try a few things out for you, as long as I am not having my op of course
     
  9. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    I clicked on your link but nothing came up. You do what you think is best. The way I described reminds me of a problem given us in a lab when I was getting my degree in electronics engineering. It works.
     
    Cris909 likes this.
  10. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    You seem to have double posted. My response is the same as above.
     
  11. Cris909

    Thread Starter New Member

    May 4, 2014
    28
    1
    I will definitely try the approach your suggesting. Luckily I have a little time to experiment.
    I appreciate your help.
    There's alot of research I need to do.
     
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