Low Pwr 60kHz WWVB transmitter using NCP1200P60?

Discussion in 'Wireless & RF Design' started by johncouture, Nov 23, 2015.

  1. johncouture

    Thread Starter New Member

    Dec 5, 2010
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    I am trying to make a very low power RF transmitter to set clocks in my house. I have the Arduino code figured out to turn the carrier on and off for the date/time (that was easy). I was thinking of using the NCP1200P60 chip to generate the 60kHz carrier. Admittedly, that is the limit of my RF knowledge.

    The NCP is is a DIP8 chip designed to produce a PWM signal at exactly 60kHz. How do I wire it up so that I can dedicate a digital pin on the Arduino to switch that carrier on an off. ... Or am I so far off base that it is a stupid idea?

    My understanding of the 60kHz band is that you would have to have a large antenna and a lot of power to cause any interference with the neighbors' clock and I certainly don't want to piss off the FCC ... I just want to periodically (say once a week) send out a weak signal to all of the radio controlled clocks in the house.

    I did see the Instructable on the topic using the ATTiny 85
    The data sheet for the NCP1200P60 is here.

    Am I just crazy to think this is possible?
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    I don't get how carrier ON/Carrier OFF is equivalent to a 17 dB reduction in transmitter power. You do realize that a square wave is rich in harmonics and is not exactly the ideal RF carrier. How did you plan to debug this if the receiver(s) are unable or incapable of decoding your signal? What power level were you aiming for?
     
  3. johncouture

    Thread Starter New Member

    Dec 5, 2010
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    Thank you! Great questions, all of them. I freely admit I am a noob when it comes to RF. Thus, if I get your inference correct, it is not possible? I was aiming for power low enough that it would be legal and does not cause problem for my neighbors (about 500' in each direction).

    Ok, the chip was just a starting point. Can I create a 60kHz carrier wave an easier way?

    To debug I was just going to put one of the radio clocks next to the transmitter and set the time to something like yesterday or such. If the clock changes, I know it worked, if it does not well back to the drawing board.
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    You just need a 60kHz low-power oscillator (single op-amp or transistor using RC or LC) followed by a "modulator" that uses a Fet switch as part of an voltage-divider that either puts out full signal, or 0.141 of the full signal (switchable attenuator) . The gate of the FET will be controlled by your Arduino port pin.

    Here is the basic idea:

    306.gif
     
    Last edited: Nov 24, 2015
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the antenna does not need to be huge for limitted range, just use a wire wrapped around a ferite bar, should be enough for limitted range.
     
  6. johncouture

    Thread Starter New Member

    Dec 5, 2010
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    Thank you MikeML, Alfacliff.

    1) Is this the type of Transistor RC circuit you are talking about? (attached as transistor2.gif)

    2) I have a coil from a radio controlled clock that I could use as L1?

    3) Next I need to select R1/C1 so that I get close to 60kHz. Could I use a pin from the Arduino (a timer could be adjusted to 60.6kHz).

    4) For your modulation part. OK, I understand about having an MCU pin control an FET. A voltage divider made up of a 10K and 1K wired in series? But where do the resistors connect to in this circuit?

    This sounds like a fun project ... I'm not trying to be a pain, just learn about RF and coming up with a useful circuit.

    Ref: http://circuitdiagram.net/simplest-rf-transmitter.html
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    The oscillator you posted is for 100,000,000Hz (FM broadcast band ) ; you want one for 60,000Hz.
    A simple Colpitts or Hartley oscillator will work. Many example circuits...
     
  8. johncouture

    Thread Starter New Member

    Dec 5, 2010
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    Thank you MikeML. Sorry for the delay (holidays and relatives visiting).

    Found some references to the Colpitts and Hartley oscillators (http://www.learnabout-electronics.org/Oscillators/osc25.php). It looks like I bit off a little more than I can chew.

    As my experience is in software not hardware, it seems like the challenge with the Colpitts Oscillator is to get an accurate 60kHz source (i.e. a crystal). Yes I could order a crystal but I have all of these microcontrollers around here that can output a pretty reliable and stable signal, is possible to get a 60.6kHz pulse from a microcontroller, it is possible to put a resistor and capacitor on a microcontroller pin to get a sine wave?

    Hmmm. It seems I would need to be able to go from zero to 5V but then I would also have to go to minus 5V. How about using 2.5 as a midpoint (2.5 -> 0 -> 2.5 -> 5-> 2.5)?

    The Hartley Oscillator seems to need two coils and a crystal. Again, the goal is to just get a simple sine wave at 60kHz.
     
  9. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    If you build a 60kHz LC oscillator, do you have any test equipment capable of measuring its frequency so that you tweak it on frequency? Don't overlook listening for harmonics of the oscillator on an AM broadcast receiver.

    An LC oscillator should be stable enough without a crystal. If that is the case, 60.6kHz is likely close enough. In that case, you will need an LC resonant tank circuit excited by the square wave from the port pin which goes into the modulator that will drop the output level by 17db under the control of a different port pin...
     
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