AndyT’s Electronic Tips and Tricks

In the series example the voltage passes through the LED to the next one. This wiring is the typical of Christmas tree lights, one fails they all stop working.

So, the design of your LED circuit must take into account the voltage and current required to make them work.

Supply voltage can't be lower than the led forward voltage, because the supply voltage is not strong enough to drive the led(s)

Again LEDcalc.com comes to the rescue to help us with the calculations; but it is immediately noticeable that the series circuit will need at least 14v to work but the parallel circuit will work from just 4.7v. so the choice is yours for the design.

Best place to buy is from the Component Shop 

Perfect to get little points of light into difficult places & for creating tiny light effects. The actual light source can be hidden some distance away, then simply use the fibre to channel the light to where it is wanted. 

This fibre is made of plastic material, so it can be cut to the required length with a sharp craft knife, then simply point one end at the light source & the light comes out of the other. The fibre is flexible & can be bent around to reach its destination, which has no effect on the light transmission (think of it as a hose pipe but for light rather than water) Multiple fibres can be clustered around a single light source, to take light around a model.

The best light sources to use are high brightness LEDs due to the high light output from a tiny source also the fact that they run cold & so do not affect the material that the fibre is made from.

• To get the best light output make sure that the ends of the fibre are cut cleanly & square.
• To get points of light along the length of the fibre, simply nick it with a file, the deeper the cut, the more light will come out - be careful as this will weaken the fibre.
• LEDs make ideal light sources. A piece of heatshrink sleeve is ideal to hold the fibre in place at the end of the LED - although you can get away with nothing more sophisticated than a piece of sticky tape! 
• Again, I use white LED’s and then colour the end of the Fibre with a clear paint of choice.

The fibre is flexible bends of about 20x its diameter (1.0mm fibre it will bent to a radius of 20mm) tighter bends are possible, however the fibre may become permanently bent (not a problem for a permanent installation inside a model) although with very tight bends there will be some light lost through the sides of the fibre at the bend. If you need to make a tight bend it is advisable to warm the fibre, which will make it more flexible.

Fibre optics being plastic, do not like too much, therefore, great care has to be used when securing them in the model and the choice of glue used – so hot melt glue and CA are both on the excluded list. Great tip: glue a slice of drinking straw as a guide for the fibre inside the model, the fibre is held in place without being glued itself.

In the next episode I will look at constructing and testing the circuit for your model.