Original page created on 12/08/2015; updated on 18/09/2024.
Miniature LEDs in headlights (continued)
Mounting the LED in the optics
The LED must be positioned by the front of the headlight. It is therefore necessary to start by introducing the wires. At the beginning, I twisted them, but this increases the risk of breakage. Once the LED is in its housing, there is a good chance that it will get crooked. It is convenient to place again the optics in the machining support, held with a little adhesive tape, to avoid risky handling.
As soon as the LED is nearly vertical in the headlight, put a small clamp to stick the wires on the support and to prevent them from moving, then make a light check with the diode tester by stripping the free end of the three wires. In case of breakdown, it is better to start again now than when everything is glued!
With its opening facing upwards, fill the headlight with Kristal Klear — without overflowing! Personally, I add over a thin Plexiglas small cut-out glass. This slows the drying down again: I wait until the next day to go on; it gives me time to relax…
So, the next day, I slip the wires into a telephone wire sheath that I glue under the horizontal plate of the headlight. Here, I use Uhu Strong & Safe: it has to hold! Once the glue is dry, I bend the wires at 90° upwards and I put a point of glue.
It is not useless here to redo an LED lighting test. If this test is negative, all you have to do is to cry. You may try to remove the LED of the headlight by the front, the Kristal Klear being little tough… and start all over again.
Mounting the headlight on the chassis
If the sheath is properly stuck on the headlight base, the assembly should take its place as before with the light guide. In order that the whole holds in the housing, I place a little Patafix into it. The sheath is also glued to the PCB: the less the wires will move, the less likely they will break.
Then, the wires are appropriately shortened — it is good to leave some slack — then stripped and soldered to the circuit. I have retained my old modified circuit as explained previously. Obviously, as there is no longer any incandescent lamp, nor LED on this circuit, it could be much simpler (see below).
In spite of my own advice: I have kept a unique resistor to feed the two headlights (but still different for the whites and the reds), again not to have to remake the circuit. Fortunately, the brightness seems fairly well-balanced.
Once the decoder is properly set, the result seems satisfactory.
Note: the position difference between the red and white source is clearly visible. Therefore, be careful to place all LEDs in the same direction.
Overview of modifications
General view.
Close-up of the front circuit. The PCB, on which the decoder is stuck in cantilever fashion, is framed in red.
Close-up of the rear circuit. Reminder: the notches visible on the “floor” fittings of the cab are designed to allow the contact strips for the cab lighting to pass through.
By the way, I was just forgetting one detail: now, of course, there is no more light leaks under the chassis, nor in the cab!
New PCB
New electrical diagram
New circuit (updated on 8 July 2023)
A member of the Loco-Revue forum asked me for such a circuit, so I redesigned it more seriously with Kicad, in order to have it made by my favourite supplier, JLCPCB.
Click on the image to enlarge.
Please see here to get the Installation and wiring document in PDF (323 Kb).
This new circuit improvements are as follows:
- all wires coming out of the decoder are connected in order: more readable, easier to connect;
- the front circuit is 5 mm longer, which also facilitates the connection;
- each headlight has its own connection pads and each LED has its own resistor, adapted to its brightness.
Here are the references and characteristics of the LEDs used, purchased, I recall, at Electron Discount. If they are different, it might be necessary to change the resistor values. In DCC, one can always act on the output dimming.
| LED | Reference | Size | Luminosity (mcd) |
|---|---|---|---|
| White for the cab | 111 | 1206 | 500 |
| White / red for headlights | 198 | 0605 | 350 (wh.) / 100 (red) |
Some photos of the engine equipped with the new circuits
You’ll no doubt notice that the connections are clearer than before.
Note in the next photo the white polystyrene stop stuck to the motor flange to prevent the cantilevered decoder from pressing against the flywheel.
Click on the photo to get a closer view on the circuit.
Click on the photo to get a closer view on the circuit.
Note: there is a slight difference with the wiring diagram given above: the orange wire runs on the other side of the motor. So there are five wires on one side and only three on the other. This is not a problem, and the path of this wire is a little shorter.
This sheath diameter is well suited, but it is not flexible enough for my taste. If you can find a thinner one, it will be better. For example, the Viessmann electric couplings wire sheath is very good…
Warning: allow to dry thoroughly, otherwise there is a risk of copper oxidation by moisture. Or use no-solvent Pattex 100%, almost as transparent as Kristal Klear.
Document available for free as a PDF.
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