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Since the Prop can transmit to a television... — Parallax Forums

Since the Prop can transmit to a television...

M. K. BorriM. K. Borri Posts: 279
edited 2011-05-13 08:32 in Propeller 1
... how about to a 27Mhz receiver? Then you could just strap a propeller board to a RC vehicle and control it that way...

Is it worth working on?

Comments

  • M. K. BorriM. K. Borri Posts: 279
    edited 2011-05-12 01:58
    http://www.talkingelectronics.com/projects/27MHz%20Transmitters/27MHzLinks-1.html This is pretty old skool, I wonder how muh of it can be moved to software.
  • PerryPerry Posts: 253
    edited 2011-05-12 07:16
    M. K. Borri wrote: »
    ... how about to a 27Mhz receiver? Then you could just strap a propeller board to a RC vehicle and control it that way...

    Is it worth working on?

    Phill made a fantastic sw radio that uses 3 cogs to receive AM

    I made a user interface for it you can find here: http://forums.parallax.com/showthread.php?105674-Hook-an-antenna-to-your-Propeller-and-listen-to-the-radio!-%28New-shortwave-prog/page11

    You can see the recorded output recievied from a 49Mhz R/C trismitter there.

    Perry
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-05-12 07:40
    M.K.,

    The problem with transmitting using the Propeller is that the RF output is really "dirty". You've got three things working against you:
    1. The output is a square wave. That means you'll be broadcasting harmonics on higher bands.

    2. The PLLs exhibit significant jitter at most frequencies. This produces unwanted sidebands on either side of your main frequency that can easily cover the entire band.

    3. Transmitters used for RC require FCC approval.

    Experimenting with RF transmission is fine if the range is only a few feet. But the power output and antenna required for reliable RC operation could land you in hot water with the feds if you try it using the Prop.

    -Phil
  • davidsaundersdavidsaunders Posts: 1,559
    edited 2011-05-12 08:00
    I guess the big question is, how high of a freq could you produce a smooth sign wave using a couple of counters, a 3 bit resistor DAC, and a small capacitor? Could it be made smooth enough at the 20MHz to 40MHz range, in order to pass FCC?
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-05-12 08:09
    David,

    It simply can't be done that way. You can filter harmonics with passive components, but you can't get rid of phase jitter with a filter1. The only way I've found to generate clean sine waves with the Prop is by using an external RF oscillator:

    -Phil

    1. Let me qualify that: you can get rid of the effects of phase jitter with a very narrow passband filter (e.g. crystal lattice) that eliminates the sidebands. The fundamental may still be of poor quality, though.
  • M. K. BorriM. K. Borri Posts: 279
    edited 2011-05-12 08:48
    This wouldn't need to xmit more than a few inches -- the idea is to put the propeller right on top of the toy's receiver! Sort of how you can take a prop, load the tv object, and physically put the prop board near the antenna and drive the tv.
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2011-05-13 08:32
    One of the issues is that the "can " fq1236fh3.gif
    that tunes the TV station is meant to be Well shielded. SO its unlikely you will get much in to this box .

    If you did you would need a good deal of power and with that amount of power Men in black suits and antennas may come knocking ..
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