Fig.5: the transmitter encoder IC has an internal oscillator set to 455kHz by the ceramic resonator, X1, connected between pins 12 & 13. The 455kHz is divided down by a factor of 12 to give a 37.9kHz carrier frequency for the infrared LED (IRLED1). When any pushbutton is pressed, it pulls the corresponding input of IC1 low and this causes the output at pin 15 to deliver a uniquely coded stream of pulses at 37.9kHz.

Last month, we completed the circuit description of the Railpower except for the infrared remote transmitter and this is shown in Fig.5. It comprises a single IC, two transistors, an infrared LED and a few passive components. The IC’s internal oscillator is set to 455kHz by ceramic resonator, X1, connected between pins 12 & 13. The 455kHz oscillator frequency is divided down by 12 to give a 37.9kHz carrier frequency for the infrared LED (IRLED1). Current drive for the LED is provided by the Darlington-connected transistors, Q1 & Q2.

When any pushbutton is pressed, it pulls the corresponding input of IC1 low and this causes the output at pin 15 to deliver a uniquely coded stream of pulses (at 37.9kHz). The pulse codes can be changed using different combinations of links LK1 and LK2 so that you have the option of using up to four separate Railpower controllers which operate independently on the same layout.

This can be a boon to realistic operation on large layouts with cab (block) switching. Naturally the receiver coding on the main PC board must match the respective remote control transmitter in order to operate. However, if you only intend to use one Railpower controller on your layout, you can omit the two links on both the transmitter and the main circuit board.

The transmitter circuit is powered by two AAA cells connected in series to provide a 3V supply. The IC draws only about 1μA on standby, when the switches are not pressed, so the batteries should last for virtually their shelf life.