RPi Telegraph

Description

I saw a demonstration of some old telegraph equipment and thought about how simple the technology was compared to what we have today. The technology to energize electromagnetic devices at a time when electricity was barely understood was the catalyst to many inventions and innovations during middle to late 19th century. This wired technology eventually lead to transcontinental communications, teletypes, telephones, fax machines, internet, email, and finally wireless communications.

This is a tribute to the original texting device that made real-time long distance (beyond line of sight) communications between people a reality.

Currently I have two implementations. One is using an arduino, the other with a Raspberry Pi. For both I have setup a protoboard to host the LCD, contrast pot, a transistor to drive the sounder, 5vDC power supply connector, and keyer connector. I'm working to finalize the configuration and wrap it up in a 3D printed box.

Project Logs

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Schematic
Ed Danis • 06/06/2015 at 16:55 • 0 comments

This is my first attempt to capture the schematic using Eagle. I welcome any constructive input on how to improve. I'm using a 12VDC power supply and limiting the current to the sounder using a trimpot. I selected a trimpot so that I can adjust to any sounder since they have varying resistance. I put the Keyer in the same loop as the digital signal so that I can drive the sounder with either an arduino/rpi or with the keyer. I used a 5v voltage regulator to limit the voltage on the bus since it's connected to the microcontroller board. I probably need a diode there, but I have an idea I want to explore, which is to have the wire going to the microcontroller to be used to send commands back to the board.
Power Supply
Ed Danis • 05/25/2015 at 02:13 • 0 comments

I've learned (luckily not the hard way) that I need to limit the current going to the solenoids to avoid damaging the sounder. There are a number of references, but I have not yet found a definitive source on what the proper current should be. Each sounder has a known resistance, so I'm going to experiment with a 12VDC Power Supply and will move a way from using the relay shield and replace it with a MOSFET. More to come.
Power Supply Sounder Current Limiting Resistor Current Worked?
12V 20 Ohm 100 Ohm 98 mA Y
12V 20 Ohm 150 Ohm 72 mA Y
12V 20 Ohm 220 Ohm 50 mA N

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Discussions

Bruce Land wrote 08/09/2014 at 15:45

NIce! The old stuff is important! Below is a link to a picture of the backside of the statue of Ezra Cornell on the Arts Quad at Cornell University. Notice the Morse-Vail telegraph receiver from 1838. Ezra Cornell, the founder of Cornell University, was an investor in Samuel Morse's telegraph company. Cornell University was initially funded by electronic communication! http://library24.library.cornell.edu:8280/luna/servlet/detail/CORNELL~10~1~59302~106636:Statue-of-Ezra-Cornell-on-the-Arts

Are you sure? yes | no

Ed Danis wrote 08/09/2014 at 16:05

Thanks Bruce, very cool picture and nice bit of trivia that I have not heard before.

Are you sure? yes | no

Power Supply	Sounder	Current Limiting Resistor	Current	Worked?
12V	20 Ohm	100 Ohm	98 mA	Y
12V	20 Ohm	150 Ohm	72 mA	Y
12V	20 Ohm	220 Ohm	50 mA	N

RPi Telegraph

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