03-29-2010, 01:55 PM
Yes indeed they are not that new. Resistors can be used however. Just work out a matching value for your LED. If it is a 5V version, and you have a current rating, then depending what your power supply is, will determine how big your resistor needs to be. Let's say the led draws 30mA, and your supply is 12V, this means your resistor has to soak up the remaining 7 volts (12-5=7V). Your resistor then needs to be:
R=U/I equals 7V/30mA = 7 / 0.03 = 233 ohms. However, this value is not commercial available, so get the next value up from your supplier, depending on whether it is a metal or carbon resistor, you may find the value varying somewhat. ( a standard 5% carbon E24 resistor range would be 240 ohms) For more on resistor ranges see <!-- m --><a class="postlink" href="http://www.mi.mun.ca/users/cchaulk/eltk1100/resistor/stdvalue.htm">http://www.mi.mun.ca/users/cchaulk/eltk ... dvalue.htm</a><!-- m -->
Of course, the draw back is that the led won't operate to spec until you reach that 12V (or whatever applies to your supply), but in many cases, nowadays people use DCC, which has a constant supply to the tracks.
R=U/I equals 7V/30mA = 7 / 0.03 = 233 ohms. However, this value is not commercial available, so get the next value up from your supplier, depending on whether it is a metal or carbon resistor, you may find the value varying somewhat. ( a standard 5% carbon E24 resistor range would be 240 ohms) For more on resistor ranges see <!-- m --><a class="postlink" href="http://www.mi.mun.ca/users/cchaulk/eltk1100/resistor/stdvalue.htm">http://www.mi.mun.ca/users/cchaulk/eltk ... dvalue.htm</a><!-- m -->
Of course, the draw back is that the led won't operate to spec until you reach that 12V (or whatever applies to your supply), but in many cases, nowadays people use DCC, which has a constant supply to the tracks.
Be sure to visit my model railroad blog at <!-- m --><a class="postlink" href="http://www.namrr.blogspot.com">http://www.namrr.blogspot.com</a><!-- m -->