Stephen, who shops at Jaycar Brookvale
"The practical use of electricity paralleled the Industrial Revolution. An example from the 1840s is the development of the Morse telegraph. Light globes and electric motors did not come into use until the 1880s. In the 1820s, the development of trains started. Trains ran on time interval, i.e. a train would be despatched say 15 minutes after the previous train, with no idea if it had reached the next station. Accidents happened. In the 1850s railways saw the need to increased safety and the Block Telegraph was invented to regulate trains on railways to reduce accidents. This uses Block Instruments which use a simplified telegraph code using bells, and indicators to remind signalmen of the state of a “block” or section of track. By the 1870s, these evolved to give three standard indications LINE CLOSED, LINE CLEAR and TRAIN ON LINE. These instruments typically required 3 wires (plus a return), one for each track using a permanent positive, permanent negative or no signal (for LINE CLOSED) to show the status. The third wire was used for the bell. In 1900 a One Wire Block Instrument was developed which used one wire, plus a return, to send 8 different signals, LINE CLOSED, LINE CLEAR and TRAIN ON LINE plus the bell for each direction. This was achieved with changing polarity and half voltage pulses. Today this would be done with some smart electronics. Block Instruments are still in use today, including one major installation north of Melbourne. How many other examples of early electrical technology are still in use for a safety critical application. I decided that I wanted Block Instruments for my model railway. Real instruments are hard to come by and large. So I decided to build my own! Each Instrument has a range of parts sourced from Jaycar, 9 relays, a rotary switch, 2 milliammeters, 2 microswitches, a pushbutton, diodes and resistors, plus my own custom designed PCB, a metal etched face and four 3D printed components. The completed Instrument is 300 mm high While I wanted 4 Instruments, I’ve now built 18, as they are being purchased by other model railway enthusiasts looking for prototypical operation of their trains."