Iambic Morse Code Keyer Circuit Description:

08/07/2001

The top circuit is simply divided into 3 sections:

  1. The first One-Shot has a very short time interval to load the correct set of binary codes into the 2nd device, where one binary selection is a 0001 for a single dit, and a 0111 for a single dah.
  2. This second device is actually a 4-bit "pre-Loadable Shift-Register".
  3. When this shift register is loaded with the proper binary values, it immediately triggers the 3rd device into action.
  4. This 3rd device is a "Re-Triggerable" One-Shot, that when it times out, it will send a "Shift Pulse" to the Shift-Register, but before the Shift-Register can shift data down, the One-Shot will re-trigger itself into action again.
  5. In this manner, even if there is only one binary data-bit, the One-Shot will go for this second time interval, which will establish the 1 time-frame wait before another "dit" can be established.
  6. The output of the 4-bit binary shift register will be the correct duration for appropriate control of a transmitter, based on the RC time of the One-Shot (usually this is about 1/2 of the RC time constant). This of course should be adjusted accordingly for correct code speed for the keying circuit.
  7. The output of the 4-bit Shift Register should be fed either to an appropriate transistor circuit or micro-relay to key the transmitter.
  8. A very important consideration is that whether the 4-bit Shift Register is loaded with a 0001 or a 0111, there is always a following 1-bit time frame that the One-Shot adds in after the completion of the dit or the dah, to give a natural spacing before the next dit or dah.

The Lower Circuit is comprised of some interaction explained as follows:

  1. Since both dit & dah begin with the same letter "d" I have chosen the last letter of either "t" or "h" for signal representations.
  2. There is a definitive symmetry of the upper portion and the lower portion of these signals, and this symmetry represents the "Dit" v.s. "Dah" signals. It should only be necessary to indicate one of these most of the time.
  3. "/TP" represents Dit Paddle, with a grounding effect to the circuit (the slash indicates a "low").
  4. "TR" represents a Dit Request, which can be held in memory status until allowed.
  5. "TS" represents a Dit Strobe to set the "Dit Active", if allowed.
  6. This action is allowed only if "Enabled" by "TE".
  7. "TA" represents Dit Active, but "/TA"is used to feed a low into the keyer circuit to initiate the timer for a Dit Duration.
  8. A special consideration is that initially both "TE" & "HE" are enabling, until either "TA" or "HA" becomes active, and thereby toggling the enables for a "Next-Turn" condition. This is how the "Iambic" condition is accomplished.
  9. When the Timer Circuit functions are fed back into this circuit the toggling takes effect, if requested.
  10. If this circuit is placed into a metal box with good shielding, it will work well.


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Keyer.html - SfE-DCS, ddf - 08/07/2001