Robot Radio :D

Discussion in 'Wireless & RF Design' started by Art, Apr 19, 2014.

  1. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
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    Last edited: May 6, 2014
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  2. Metalmann

    Active Member

    Dec 8, 2012
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    Sweet.

    He used a stepper motor to tune?

    Kind of loud....
     
  3. PRS

    Well-Known Member

    Aug 24, 2008
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    That's a crude but cool tuner. How do you suppose it works? My guess is that a simple AM detector creates the telltale voltage that signals the presence of a station.
     
  4. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
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    Nah, my guess is that a frequency counter written into a 16F628A
    microcontroller which is also connected to the radio's tank circuit also controls
    the stepper motor which moves up or down looking for a preset frequency ;)

    It really needs a keypad though.. would be a much cooler demo.
    I could go back to using dial cord to shut it up, but it was an opportunity to use
    a stepper for the first time, which may become part of an ATU at a later stage.
    Automatic ATUs still work with a bunch of relays as far as I'm aware.

    Plus I kinda like the "steampunkness" of the brass gears.

    [​IMG]
     
    Last edited: Apr 19, 2014
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  5. PRS

    Well-Known Member

    Aug 24, 2008
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    So you built that contraption? ;)
     
  6. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
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    It was harder work bringing the radio back to life to be honest!
    All three trannies were open (including choke and speaker matching),
    One valve was smashed, and there was no real saving the original tuning mechanism.
     
  7. vk6zgo

    Active Member

    Jul 21, 2012
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    Back in the 1930s they really did make radios with motorised tuning.
    You had to preset (program?) the stations,though!

    I think they discovered it was too fault prone & expensive,& it died out.
    Much simpler mechanisms were used in the "Pressmatic" car radios & many European domestic sets.
    The button "push" provided the mechanical power to shift the tuning!:D

    When I first joined the old PMG's Dept,we had Auto-tune HF ISB Transmitters as a standby to the landlines between Perth & Melbourne,& Perth & Exmouth.

    The Melbourne one,made by STC,would tune itself up using phase comparators,which controlled "Carpenter" relays,which,in turn controlled the tuning motors.
    After it tuned the PAs it would adjust the Loading (Coupling).

    It was so sensitive that if the wind shook the Rhombic around a bit,it would make a minute readjustment to the Loading.

    The PA tuning on the AWA one for Exmouth were just presets,but it had an auto load circuit,& would do the same "Twiddle" when the antenna moved in the wind.

    The Standby for this service was a smaller AWA one which had all the same "goodies" as the STC,but used power transistors in place of the Carpenter relays.
    We had a lot of problems until we replaced all those transistors with better ones.

    An interesting touch with this one,is that it would "wind" its own PA coil.
    The former rotated ,& a Beryllium copper strip would be drawn out of a "reservoir",so that you had the correct number of turns.
     
    Last edited: Apr 21, 2014
  8. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
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    I do remember seeing one of those, it was a big timber console that even had a wired remote.

    I decided to keep this one together and cleaned it up so it's at least one piece.
    It could still teach me things yet, I want to do a magic eye valve, and from there,
    the micro should be able to tell when it's actually tuned to a station, rather than just
    tuning to a frequency.... and there's still room on the right for a keypad to enter a freq.

    [​IMG]
     
  9. PRS

    Well-Known Member

    Aug 24, 2008
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    Couldn't you just use a detector at the IF output and then a comparator to detect the signal? This way you would just sweep the tuner with your stepper then stop at a station and fine tune it to the highest voltage.
     
  10. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
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    That does sound like something I want to do... hope you'll be around to help :D
    But I want to add a magic eye first and go from there.
    Not to tune the radio from, but to build the initial list of frequencies.

    An idea my ham club trainer had is compiling a list of all AM radio stations and
    their frequencies in my continent (Australia), and a radio should be able to roughly
    determine it's location based on what station it can receive without any need for GPS.
    Cheers, Art.
     
  11. vk6zgo

    Active Member

    Jul 21, 2012
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    You should already have a detector to do that.
    Most radios have either an additional diode for AGC,or take a sniff off the regular one.

    When you are tuned to a station,the AGC voltage adjusts the Radio's IF & (in most cases) RF gain,so that Stations all have pretty much the same audio---this saves messing with the volume control,which you need to do with simple receivers.

    You should be able to use that to tell your micro that you are on frequency.
    Obviously,you need to be able to defeat that function while you are actually
    tuning,or the thing will always stop at the first station it comes to.
     
  12. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    The closest I've been of something like that was a small console (seemed to be kind of an embedded module) that the operator used to "dial" the frequency he needed the xmtr to transmit at.

    I used to have the rotary thing somewhere around. Ericson maybe? Not sure.

    Minimum 50 yo++

    Much more cruder were modules to be inserted somewhere in the body of the transmitter to change the frequency. Shore to ship, mostly.

    Three of them waiting to be binned or maybe disassembled in the next days to free some space.
     
  13. PRS

    Well-Known Member

    Aug 24, 2008
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    The scanner with my car radio has two buttons. Push the right arrow button if you want to scan upward with respect to frequency, or the left to scan downward. This would mean two debounced switches on two pins of the microcontroller. The logic is a simple program. Press the right switch and the stepper rotates the tuner in the direction of higher frequency. When a station is sensed via the detector it stops. If you don't want that station just push the button again and up the tuner goes until another station is detected, and so on.
     
  14. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
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    PLL radios also have presets which store a frequency.
    It might make a more impressive demo to do the scan,
    but once you have your favourite stations it would be quicker to enter them on a keypad,
    or to enter a number (say 0-9) that represents a preset frequency.
    I suppose it wouldn't hurt to do both once the second part of the circuit is done.

    PRS.. with regard to your other thread about antennas.. funny thing..
    This morning I took the longest ferrite loop antenna I have (from a 60's radio),
    connected it's coil parallel to another old tuning gang I have,
    then connected that between the earth and antenna connections of this radio.
    Best tuned AM broadcast antenna I've got yet! :D
    I've read that you can connect them internally, replacing the first coil in
    pre-ferrite loop AM radios.



     
  15. Metalmann

    Active Member

    Dec 8, 2012
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    I used to have a couple of radio/reel to reel tape recorders, which used the "Magic Eye".
    Even had a few "wire recorders".:cool:
    Very cool to watch the eye, while I laid down a few guitar, bass, and keyboard tracks.

    Back then, to do multi-tracks; you had to use at least 2 separate tape machines.

    Could be quite tricky at times.:D
     
  16. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
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    Or a four track with simul-sync :D
    Got this one a couple of weeks ago :)

    [​IMG]
     
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  17. PRS

    Well-Known Member

    Aug 24, 2008
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    It sounds like we're reinventing the scanner. I think Art wants to do something entirely different. Once you catch on to microcontrollers it seems like the sky is the limit. I was thinking of making a miniature elevator from floor to ceiling; it would have to be a show piece in order to really wow people. Maybe like a cuckoo clock -- a bird came out and cuckooed each time the car stopped.
     
  18. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
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    As close as possible to modern PLL radios sounds good.
    Up & down for a freq, or scan. Then push and hold a number to preset a freq (write it to EEPROM).
    But also, being able to enter an arbitrary freq is good... then the same thing could be applied to
    tuning an analogue VFO for a ham radio.. coz we F calls can't modify or connect a computer to a radio ya know :D
    but maybe I can make a robot turn the dial to make it stable.
     
  19. PRS

    Well-Known Member

    Aug 24, 2008
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    An arbitrary entry? I'm sure you already know you'll need a keypad, Art. Just what is a magic eye?
     
  20. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
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    If you were around for valves/tubes, you might have called it a cat's eye:
    https://www.youtube.com/watch?v=rk9JtEKQqxM

    Working on the keypad now.. not many spare pins on the main micro left,
    but I can use another one for the keypad, and just send commands to the main one serially.
     
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