
L.E.D’s (Part Two)
Wiring Up L.E.D’s Part two
In this article we’ll look at how to wire up L.E.D’s. On wiring diagrams L.E.D’s can be shown like so:
L.E.D stands for light emitting diode which means that they are very much like their diode counterparts, they’re polarized. But how do know which is the positive & negative on an L.E.D? There are a handful of ways for finding the positive and negative pins on an LED. Usually the longer leg on the L.E.D. is the positive, & the shorter leg being the negative. This should indicate which is which. The image below shows one such example
But if someone has trimmed the legs, then another way to find the positive is to try finding the flat edge on the LED’s outer casing. The pin nearest the flat edge will be the negative, cathode pin. Below we’ve marked the positive in orange to show this.
If a L.E.D. is incorrectly wired then it won’t light/work.
Single L.E.D
If using a power supply above 3 volts the standard practice is to install a resistor on the positive side of the L.E.D as shown on the right. When fitting a resistor always use a minimum rating of 1000 ohms upwards. In the diagram on the right you can see that the resistor has been fitted on the positive wire that runs from the wiring bus to the L.E.D.
Multiple L.E.D’s Same Colour & Type
Ideally each L.E.D should have it’s own resistor, however if L.E.D’s are used in parallel then one resistor on the positive supply as shown on the right can be used. You can use 1 X resistor for many L.E.D’s for all that is being powered, it is limited by the total current draw Versus the supply voltage & the choice of resistor used. See Ohms Law for more details:
For example if using a 12 volt supply powering say 10 L.E.D’s, & your using a 1000 ohm resistor & the resistor is running hot then try using less L.E.D’s in the circuit.
Two L.E.D’s Same Colour & Type
Ideally each L.E.D should have it’s own resistor as shown on the right. The diagram shows an example where L.E.D’s are being used as an indicator, such as showing which way the points are set on a control panel. When the polarity is changed one L.E.D will turn off & the other will light up. The resistor should be both of same type & rated value, whilst the L.E.D’s should be of the same type of characteristics.
Two L.E.D’s Different Colours
Ideally each L.E.D will need it’s own resistor that is appropriate to it’s efficiency, so the circuit will balanced & the lighting levels will be the same on both L.E.D’s as shown on the right.
The diagram shows an example where L.E.D’s are being used as an indicator, such as showing which way the points are set on a control panel. Other uses for example are: Showing polarity indicator, control panel, colour light signal status. When the polarity is changed one L.E.D will turn off & the other will light up.
Two Coloured L.E.D With Three leads
For a bi-coloured L.E.D with three leads, the two leads as shown will need an appropriate resistor to it’s efficiency to balance the circuit & also keeping the two light levels in balance too.
The diagram shows an example where a bi-coloured L.E.D is being used as an indicator, such as showing which way the points are set on a control panel. Other uses for example are: Showing polarity indicator, control panel, colour light signal status. When the polarity is changed one colour will light & the other will turn off.
Two Coloured L.E.D With Two leads
For a bi-coloured L.E.D with two leads, the two leads as shown will need an appropriate resistor to it’s efficiency to balance the circuit & also keeping the two light levels in balance too.
The diagram shows an example where a bi-coloured L.E.D is being used as an indicator, such as showing which way the points are set on a control panel. Other uses for example are: Showing polarity indicator, control panel, colour light signal status. When the polarity is changed one colour will light & the other will turn off.
In Part three to follow we’ll look at some simple L.E.D switching circuits.
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