Tag: telegraph makecontroller
Telegraph Power Requirements
by Charles on Apr.03, 2009, under Electrical Engineering
Side picture of Bunnell telegraph in the Boston Productions studio.
Recently I have had the pleasure of getting to work with an authentic working telegraph from the early 1900s. From what I understand this is a Bunnell railroad telegraph key and sounder. We purchased it for a project that is underway in New York.
Testing the sounder around the office we have simply been using a 9v battery. However, eventually this will need to be driven by a microcontroller. Until I was able to experiment with the apparatus, I had been trying to guess how much amperage it takes to cause the coils to generate the magnetism needed for the sounder to work. The actual wood that the key and sounder are mounted on states “4 ohms”. After testing and poking around a little bit, I think this model requires about 350mA to create the electromagnetic effect and produce a sound.
Vertical view of a Bunnell Railroad Telegraph.
Currently we are using the MakingThings Make controller coupled with a high watt rated 10ohm resistor in order to do some initial stress testing. The Make Controller’s output drivers can source a maximum of 1 amp. I currently have the outputs set to 5v. If you combine the resistance written on the wood of the telegraph with the resistor (10 + 4 = 14), you get 14ohms total resistance. Use Ohms law 14ohms/5v and you get .357A or about 350mA.
The ultimate goal is to have the telegraph activate upon the sense of motion. For this purpose we are planning on using the popular Arduino, but I am going to have to make a more powerful driver shield for it in order to source the current needed to run the telegraph.
