ABC TELEGRAPH COMMUNICATOR TESTER, 1850's

The ABC telegraph was an early form of communication where an arm was turned to a letter sometimes by a pulse, and sometimes by buttons opposite each letter, the arm being held by a return spring and latched on the letter required, a button was pressed releasing the arm which returned back to the beginning sending a number of pulses relating to the letter chosen i.e. the letter C would give 3 pulses the letter B would produce 2 pulses. The receiving unit would be driven by an internal solenoid counting the arm up to the required letter, after each letter was sent it was necessary to reset the unit and start again, sometimes this was achieved automatically. Such units were used while Morse code was being devised, around the 1840's, and continued in some countries long afterwards. This unit was simply a testing device for checking received signals only.

• A Short History of Telegraphy
  
• Science and Society Picture Library
  

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