Telautograph

Surprisingly, at least from a modern perspective, some early telautographs used digital/pulse-based transmission while later more successful devices reverted to analog signaling.

Gray started experimenting in 1887 with analog transmission of the pen position signals using variable resistances[4] as was done in previous devices, but was dissatisfied with the performance he achieved.

Gray's early patents[6][7] show devices to accomplish the required functions over two line wire circuits with a common ground connection.

It's clear how challenging the technical problem was; a later film of a similar device[20] shows the rapidity with which an operator might move the pen.

George S. Tiffany on behalf of the Gray National Telautograph Company understood the significance of the AC signal quite well.

This principle is in common use today in the form of dither, as applied to proportional pneumatic and hydraulic control valves and regulators.

A dither signal can overcome both magnetic hysteresis and static friction and was preferable to mechanical vibration, as later Telautograph designs[28] used it exclusively.

Apparently this technique worked well, because even though Tiffany studiously avoided every constructional feature of Ritchie's patent, he used the exact same fundamental technique, and the analog telautograph principle continued to be used for at least the next 35 years,[22] such as in those installed in the Frick Art Reference Library around 1935,[29] also see interior view.

[25] All available images and descriptions of commercial telautographs after 1901 depict the open loop analog devices that Ritchie pioneered.

The telautograph became very popular for the transmission of signatures over a distance, and in banks and large hospitals to ensure that doctors' orders and patient information were transmitted quickly and accurately.

[34][35] The teleautograph network in Grand Central Terminal included a public display in the main concourse into the 1960s; a similar setup in Chicago Union Station remained in operation into the 1970s.

An example of a telautograph machine writing script can be seen in the 1956 movie Earth vs the Flying Saucers as the output device for the mechanical translator.

The Allpoint Pen is currently in use and has been used to register tens of thousands of voters in the United States,[36] and the LongPen, an invention conceived of by writer Margaret Atwood, is used by authors to sign their books at a distance.