Saturday, April 01, 2017

How I made some loco lamps


When I recently Anglicised my LGB Stainz loco, I decided to replace the large lamps on the front and rear of the loco with more UK-looking lamps. I decided to use a similar approach to that which I adopted when making lamps for my semaphore signals (see How I made some semaphore signals).

The lamp bodies

 A piece of 8mm Plastruct square tube was marked 12mm from the end.

 A cross was then marked on one side to find the centre.

 A 2mm hole was then drilled in the centre and through the opposite side.

The hole on one side was then enlarged to 5mm using a triangular needle file. I find this easier to control than using a 5mm drill bit.

I repeated this process another three times.

The body of the lamp was then glued to an off-cut of 1mm thick plasticard.

... which was then trimmed to neatly fit on to the top of the lamp.

NOTE: At this stage, I have now learnt from experience to paint the interior of the lamp with black paint to help prevent light from shining through the translucent plastic.

1 1mm hoop of 6mm Plastruct tube was then cut ......

.... and glued to the front of the lamp (The 5mm LED was inserted to ensure the ring was centralised while being glued).

 A 6mm square of 1.5mm thick plasticard was then cut out .............

............. and glued to the top of the lamp.

A 3mm length of 4mm Plastruct rod was then cut........

...... and glued to the top of the lamp.

The lamp was laid on its side and a 1mm hole drilled in the centre the sides of the 1.5mm thick capping piece ........

.... and a piece of 1mm brass rod was then bent to shape and inserted to form a handle.

Wiring up the LED

 As I would be using a 12v supply for one of the lamps, a 1k resistor was soldered to one leg of the LED and a plain wire soldered to the other leg ......

 ..... and then the leads were shrouded in 1.6mm heatshrink tubing and heat applied to shrink the tubing.

Two of the lamps were wired with bi-colour (red/white) LEDs. These were going to be powered with a 3.2v supply from the Deltang Rx65b directional lighting output pads (P1 and P2). For these LEDs, a 270 ohm resistor was soldered to the middle (cathode) leg of the LED and red and grey (because I didn't have any suitable white) wires soldered to the other legs (anodes) so I would be able to differentiate between them when wiring up the loco.

NOTE: This online LED resistor calculator is very helpful in helping to advise on the correct value for the resistor -
  1. Select the type of LED you are using from the drop-down list
  2. Click on the 'Get LED details' button
  3. Change the 'Battery voltage' value to that which you intend to use
  4. If required, change the 'Typical LED current' value (20mA is usually maximum brightness for LEDs, I prefer to change that to 10mA to give a more realistic level of light output)
  5. Click the 'Calculate Resistor' button
  6. The value of  resistor will then be shown below the button

The lamps were then fitted into place on the loco and the wiring led back the Deltang Rx65b receiver/controller.

When the loco moves, both lamps at the front of the loco show a white light and the upper lamp at the rear of the loco shows a red lamp (the lower lamp is extinguished). The wiring for this operation is very straightforward:

The lower lamp was connected to output pad A and the positive supply from the battery. Pad A gives automatic forward lighting and also mirrors the receiver's own LED. When the receiver is hunting for the transmitter signal it flashes once a second, when it is bind mode it flashes rapidly and if the loco battery falls below its safe level of charge the LED flashes five times, pauses, five time etc. Once the receiver has locked on to the transmitter then the LED performs its normal directional lighting function.

The other lamps are connected to output pad 1 (to provide forward lighting) and output pad 2 (to provide rearward lighting). As the upper lamps have red/white bi-colour LEDs, I wired them up so that the leading lamp would glow white and the trailing lamp would glow red. The bi-colour LEDs have a common cathode (negative) leg which needed to be connected to the negative supply from the battery. This is why it was connected to pads 1 and 2 to provide the directional lighting as these pads provide 3.2v outputs whereas Pad A provides a 0v output when energised.

For more information on using the output pads on Deltang receivers see Using output pads on Deltang receivers.

These lamps are not highly detailed but I am pleased with their appearance - they certainly fit my criteria of the 10 yard rule (especially with eyes half-closed)!


Unknown said...

Hi Rik I am just in the process of doing a similar lighting setup with bi-colour LED's but found that mine have a common anode (+ve) connection and earthing each side lights them up, I can do this manualy but would like to use deltang rc, can you suggest how I might achieve it with an RX65.

Jon Geraghty.

Ge Rik said...

Hi Jon
You should be able to do it using the A and B outputs from the Rx65. These give directional lighting with 0v outputs. You'll need to calculate the value of the resistor based on your battery voltage,