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IR Switches, LED Lights and Resistors

HO enthusiast Don has sent in two questions for readers:

1. “IR switches have three wires coming out, think that the center one would be positive and the other two would positive out too one side or the other,  is this a momentary or a constant supply ? And, should there be a resistor on the IR switch?”

2. “I have a number of led bulbs, and a number of small led fixtures, information is connect a resistor to the bulbs, is that to each bulb  or a number of them in a group or collection of them.  Is there a + and – to each bulb?”



4 Responses to IR Switches, LED Lights and Resistors

  • Kevin Chingsays:

    Hi Don I’m not sure what the switches polarity are best use a multi-meter but i would suggest the center wire is negative and the other two positive The longer lead on the leds is connected to the positive wire

  • Kevin Chingsays:

    Also connect a current limiting resistor to the led for 12 volt use a 470 ohm resistor.

  • Dr. Phool Singh Chauhansays:

    Hi Don,
    1. You please consult the datasheet of IR switch or post the device number or ID written on it so you may be given proper information for using it.

    2. LED has polarity so you may have to take care. Cathode lead is shorter and have a notch or flat indent on plastic package and is to be connected to ‘-‘ of supply. Other lead is anode and is to be connected to ‘+’ of supply with a suitable resistor in series. Typical LED, used in model RR, draws about 10 mA current for glowing at normal intensity. Higher currents may shorten life or damage the LED. There are LED packages available for higher currents for domestic or industrial lighting use. applications.

    Value of series resistor may be calculated by using formula ‘[R=(V-Vled)/0.01] Ohm’. As example for 12 Volts supply for Red LED (Vled=1.6 Volts) the value of R= 1040 or 1K Ohms.

    There are also LED available with integrated series resistor for different supply voltages. You may check the value of Vled for LED available with you. You should have a variable DC power supply. Set the supply to zero volt and connect LED taking care of polarity as mentioned earlier with a multi-meter in series in mA mode to monitor current. Increase the voltage slowly and note down the value when LED starts glowing and current is about 10 mA. The supply voltage will be Vled. You can use this value in the formula and calculate the value of R for any LED with you.

    It is better to use separate resistors for each LED bulb. However you may connect several LED bulbs in series with ‘-‘ of first to ‘+’ of next LED and calculate the value of resistor by multiplying Vled by number of LEDs. The value of total Vled should be less or equal to your supply voltage!

  • W Rusty Lanesays:

    I use LED´s for all my lighting even on engines. It does not matter which side of the LED has the current limiting resistor connected–just make sure you use one. Also to prevent premature LED burnout from the engines electromotive force a diode placed in line with the current limiting resistor would prevent this. When the engine moves forward the LED lights up. But when you reverse the engine the LED will flicker and the diode inline with the LED will block the current going to the LED and stop the flicker and prolong the life of the LED.

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