morse code tranceiver, help needed urgently

Discussion in 'The Projects Forum' started by alan-1981, Jan 22, 2007.

  1. alan-1981

    Thread Starter New Member

    Jan 22, 2007
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    need help on my morse code
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    Can I assume that the optical fiber portion of this design is using off-the-shelf parts such that the electrical signal from your morse code key interface circuitry is feeding into the optical fiber transmitter and the other end of the optical fiber is connected to a fiber optic receiver so that all you need to do is deal with the electrical signal at the receive end and process it so that you display the ascii text on computer monitor?

    hgmjr
     
  3. alan-1981

    Thread Starter New Member

    Jan 22, 2007
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    heya thanks for replying its fairly urgent at moment. ya i was basically thinking of just switching the led for the fibre directly from the keyswitch via some transistor or mosfet, also for switch debouncing i will use a spdt spring return switch onto an sr flipflop this will switch the mosfet and inturn the led. it will be up to the operator to vary the time that the swich is depressed for to give you a dot dash or space there is also an intercharacter space but both these will be the absence of a signal for a certain multiple of clock pulses. the dash will be 3 times as many clock pulses as the dit. and a space the absence if a signal for between 5 and 7 clock pulses, so i was thinking to keep the transmitter simple that is all i would use and once i had recreated the inputted signal on the receiver via my transimpeadence amp and photodiode that is where im stuck. i will use some sort of counter to divde the freq. of my clock down to a fairly slow freq. i just dont know how to handle this serial data stream using a shift register and eprom and need fairly step by step advice for this stage. and all parts will be off the shelf, thanks for your help
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    282
    Hi,

    Do use an R-S debounce on the Morse key. That will make life much easier.

    An outfit named TAOS makes TO-92 packaged light-to-voltage converters. They are available through Mouser, starting at $1.27. They respond to wavelengths from 1050 nm to 240 or so. Use onw for a receiver and you can run the fibre link with any LED in the drawer.

    Be prepared for hair-pulling getting the dot-dash intervals into the computer. Everybody pounds a key differently, so an extremely rigid interval may prove difficult. You may need to look for long-short ratios to get good Morse code in.

    Don't forget the Morse-to-ASCII lookup table.
     
  5. alan-1981

    Thread Starter New Member

    Jan 22, 2007
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    heya ya thanks a million, just wondering if ya have any ideas about the what to do with the signal after that if i put it into a shift register and from there onto an eprom would this work or do i need intermediate electronics?
     
  6. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    alan-1981,

    How many characters do you expect the shift register to hold at any given instant?

    An eprom would serve the purpose of handling the MORSE to ASCII conversion but I think a static random access memory or SRAM would be more useful as a character storage medium. If it is important to retain the message following a power on/off cycle then you could use a battery backup scheme.

    I would echo beenthere's comments pertaining to the keying speed. I wonder if you could use a manually adjusted sampling clock frequency to dial in the correct sample rate for a given sender. You would adjust the frequency until the morse code stream was intelligible.

    Too bad about the the "no-PIC" rule since that would provide a number of options that will be denied you in a discrete digital-logic only implementation.

    How soon does this project have to be completed? Also, Are you expected to take the design all the way to implementation or just draw the schematic of the circuit?

    hgmjr
     
  7. alan-1981

    Thread Starter New Member

    Jan 22, 2007
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    i was going to use a 555 timer with a frequency of about 5khz and divide the frequency down to an appropriately low level so as to only use 1 character for a dot and 3 charcters for a dash as well as some piece of logic to signal end of character. it is also possible for me to just display each character on a seven segment display. it is due in 2 weeks time. obviously a serial in parallel out shift register is most appropriate but this will still need about 20 places minimum, as to represent a '0' in morse is 5 dashes so this would be something like 00000 111 111 111 111 111 with the 5 trailing zeros used to represent end of character and for example th letter q is 00000 111 111 1 111 something like that any way. we are restricted to using eproms unfortunately. just a point to note that i dont think they are looking for anything too fancy and the main marks go for having a circuit designed wth building on a board a bonus afterwards. any ideas?
     
  8. hgmjr

    Moderator

    Jan 28, 2005
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    You will need to use a different display than a 7-segment since you need a display capable of alphanumeric characters.

    hgmjr
     
  9. alan-1981

    Thread Starter New Member

    Jan 22, 2007
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    im not too worried about displaying the text once i get it into binary or ascii from the eprom i should be sorted from there, my main problem is converting the serial morse into legible ascii
     
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