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Railpower Model Train Controller, Pt.2

Last month we presented the circuit, specifications and parts list for our new high-performance Railpower IV model train controller. Now it's time for the construction details - and we show you how to set it up for best performance.

By John Clarke

onsidering that the new Railpower IV has such a lot of features and gives great performance, its construction is relatively simple compared with our previous Railpower designs featured in 1988, 1995 and 1999. This is mainly as a result of using the PIC16F88 microcontroller.

Click for larger image
Here’s the two-line alphanumeric display (in this case the Jaycar model with backlight) which gives you all the information you need about your settings. Here it is showing the train speed at about 56% of the maximum speed set (90%). Inertia is on (indicated by the "I") and the lock is on (shown by the padlock being closed). As you enter other modes, the information on the display changes to reflect those modes.

And whereas our two previous designs used front panel LEDs and an analog meter, this latest design uses a 2-line alphanumeric LCD panel.

All our previous designs used one large PC board but this latest Railpower uses two PC boards. The main board accommodates the power transformer and most of the circuitry, including the microcontroller, while the vertically-mounted display board is for the LCD panel and four pushbutton switches. The main board measures 217 x 102mm and is coded 09109081while the display board is coded 09109082 and measures 141 x 71mm.

These PC boards are housed in a plastic instrument case measuring 260 x 190 x 80mm. The rear panel is made from aluminium sheet. It provides heatsinking for the four Darlington power transistors used in the H-bridge motor drive circuit.

You can begin construction by checking each of the PC boards for defects such as shorts or breaks in the copper tracks and to see that all holes have been drilled correctly to suit the various components. The holes for the mounting screws, the LCD mounts and for REG1 need to be 3mm in diameter. The four holes to mount the transformer are 4mm in diameter.

Note that there are different mounting positions for the Altronics and Jaycar LCD panels (the board has been designed to accommodate either).

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