My lighting circuit
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This page explains the simple circuit that can power internal carriage lighting (any track power system), or loco lighting where DCC is not in use. Note - aimed at people with some electronics skills. If you would like me to make you some, please contact me. Details: Very simply, a bridge rectifier or single diode, smoothing capacitor, a mini 5V regulator, then the light (in my case, LEDs) The completed circuit can fit in a space of around 2 x 1cm, depending mainly upon the size of the filter capacitor. Use: There are 2 scenarios where the 2 circuits could be used - for constant internal lighting of a rail vehicle. This circuit uses the bridge rectifier, so regardless of rail polarity, the lights will be powered (as long as track voltage is greater than 6.5V) On pulse power or unfiltered controllers, the lights will work at low speed due to the higher, but brief voltage peaks in the pulse or unfiltered supply. This circuit can drive up to 5 LEDs (more than enough for the intended application). In non-DCC use, directional lighting (loco headlight, marker lights, or other vehicle with marker lights) will operate depending upon track polarity. It will work on DCC, but as the track voltage does not change, the desired effect may be back-to-front). A single diode blocks the track voltage when the lights are not intended to be used - so that when the train runs in a certain direction, the appropriate lights illuminate. In the reverse direction (track voltage polarity reversed), the lights do not work. It works in an identical manner to the above circuit, except the bridge rectifier is now a single diode. Example uses: A loco that always leads a train, can have the headlight circuit as above. It can also have red marker lights on the rear. To make this look realistic when running in the reverse direction, a second circuit with headlight and marker light wired opposite to the first can be used. Optical fibres as light guides:I use a number of different sized plastic optical fibres as loco headlights and marker lights. I prepare the LED by flattening the top slightly, then drilling a shallow hole into the end of the LED to accommodate the optical fibre. Most of the LED is a casing, and care must be taken not to drill into the actual light source. For strength, I tape a small loop around the LED and fibre/s, then fill with glue to add mechanical strength. The end of the fibre must be cut as straight as possible for maximum light transmission. A sharp knife does the trick. Once set, from the inside of the model body, the fibre is fed to the outside so that it protrudes out, clear of the model. With the heat of a soldering iron tip held near the protruding fibre, the end is melted slightly and a "mushroom" effect makes a nice round light lense. Once happy with the result, the fibre is pulled back inside the model body and secured. The electronics are secured in a discrete location, and the LED and surrounding area are blackened with paint so that unwanted light does not illuminate the interior.
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