I have
documented the characteristics of various LEDs I use, or plan to use, for building & street
lighting, signals and traffic lights.
I have decided to use a standard 5v switched power supply and use LEDs at about 5mA.
The Light-DEC modules requires different power sources, but I plan to use 'buck' converter to reduce that to the same 5v and 5mA target where possible.
A buck converter (step-down converter) is a DC-to-DC power converter which steps down voltage (while stepping up current) from its input (supply) to its output (load).
R = (Vsource - Vled forward voltage) / I
e.g. R = (5V - 3.2V) / 5mA = 2.8 / .005 = 560 Ohms
In order to illuminate various models (mainly Faller), I decided I need some bulk LEDs. I bought 1000 5mm White and 1000 5mm Warm White diffused LEDs from eBay, sourced from China, for 10.88 and 11.49 GBP respectively. They only took one week to arrive !!
The specifications are as follows:
| Quantity | 1000 pcs |
| Emitted Colour | White Diffused |
| Size | 5 mm |
| Lens Colour | White |
| Peak Wave Length (nm) | N/A |
| Forward Voltage (V) | 3.0-3.4 |
| Reverse Current (uA) | <=30 |
| Viewing Angle | 100-120 Degrees |
| Max Power Dissipation | 80mw |
| Max Continuous Forward Current | 30mA |
| Max Peak Forward Current | 75 mA |
| Reverse Voltage | 5-6 V |
| Lead Soldering Temperature | 240°C (<5°C ) |
| Operating Temperature Range | -25°C to +85°C |
| Preservative Temperature Range | -30°C to +100°C |
Testing a small sample of four using a 5 Volt power supply and a 330 Ohm (measured at 325 Ohm) resistor gave the following results:
| White LED | Vf = 2.82 ± 0.02 | I = 6.39 ± 0.02 mA |
| Warm White LED | Vf = 2.77 ± 0.02 | I = 6.55 ± 0.02 mA |
I bought four boxes of "500pcs 3mm Ultra-Bright LED Light Emitting Diode Component Kit for PCB Circuit" from eBay, sourced from China, for 14.44 GBP, including p&p. They only took ten days to arrive !!
The specifications for each box is as follows:
| Red | Yellow | Green | White | Blue | |
|---|---|---|---|---|---|
| Quantity | 100 pcs | 100 pcs | 100 pcs | 100 pcs | 100 pcs |
| Size | 3 mm | 3 mm | 3 mm | 3 mm | 3 mm |
| Wave Length (nm) | 620-630 | 580-590 | 520-530 | 610-620 | 460-470 |
| Forward Voltage (V) | 1.9-2.1 | 1.9-2.1 | 3.2-3.4 | 1.8-2.2 | 3.2-3.4 |
| Current
(?) |
20 mA | 20 mA | 20 mA | 20 mA | 20 mA |
| Intensity (mcd) | 3000 to 4000 | 5000 to 6000 | 10000 to 12000 | 3000 to 4000 | 3000 to 4000 |
Testing has been done on a small sample of four LEDs of each colour using a 5 Volt power supply and a 470 or 330 Ohm resistor gave the following results:
| White | Red | Blue | Green | Yellow | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Resistor | 470 | 330 | 470 | 330 | 470 | 330 | 470 | 330 | 470 | 330 |
| Vf | 2.76 ± 0.01 | 2.80 ± 0.01 | 1.96 ± 0.01 | - | 2.78 ± 0.01 | 2.84 ± 0.01 | 1.98 ± 0.02 | - | 2.01 ± 0.02 | - |
| I | 4.67 ± 0.01 mA | 6.49 ± 0.01 mA | 6.35 ± 0.01 mA | - | 4.62 ± 0.01 mA | 6.35 ± 0.01 mA | 6.20 ± 0.09 mA | - | 6.25 ± 0.05 mA | - |
| Description | Number of | Red | Yellow | Green | Resistor | |||
|---|---|---|---|---|---|---|---|---|
| or Make | Aspects | V | mA | V | mA | V | mA | Value |
| China (eBay) | 2 | 5 | 3.1 | - | - | 5 | 2.2 | 1k0 |
| China (eBay) | 3 | 5 | 3.1 | 5 | 3.0 | 5 | 2.2 | 1k0 |
| Kyle | 2 | 5 | 3.1 | - | - | 5 | ? | Built-in |
| Kyle | 3 | 5 | 3.1 | 5 | 3.0 | 5 | 2.5 | Built-in |
| Kyle ground | 2 | 5 | 3.1 | - | - | 5 | 2.5 | Built-in |
| Gaugemaster | 2 | 5 | 3.1 | - | - | 5 | 2.5 | Built-in |
| Gaugemaster | 3 | 5 | 3.1 | 5 | 3.0 | 5 | 2.5 | Built-in |
| Conrad (Obsolete kit) | 3 | 5 | . | 5 | . | 5 | . | Not yet built |
| CR Signals Platform | 2 | 5 | 0.57 | - | - | 5 | 0.45 | 5k6 |
| CR Signals kn02 (kit) | 2 | 5 | . | - | - | 5 | . | Not yet built |
| CR Signals kn01 (kit) | 3 | 5 | . | 5 | . | 5 | . | Not yet built |
Details on addressing can be found here starting at address 905.
| DCC | LED voltages | |
|---|---|---|
| On (+) | pin 1=5v | pin 2=0v |
| Off (-) | pin 1=0v | pin 2=5v |
| Max Current | 50mA per output | |