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Using Light Emitting diodes or "LED's" |
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LEDs function in much the same way as any other diode ( or "rectifier") -they conduct electricity in only one direction. |
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LEDs emit light when they conduct, which is their main use (which is just as well as they make poor diodes) . When an LED conducts, it has a fixed forward voltage (called Vf ) is used in conjunction with a resistor to limit the current to a desired value. |
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| Vf can typically range from 1.2 to 3.2 volts and the maximum current they can handle ranges from around 10mA upto 30mA | |||||
| It is important that the resistor is used and that the LED is connected the right way around . A flat on the side of the LED body shows the "negative" side | |||
| Typical values | 4 cell Nicad (5v) |
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| Vf =3.2v Imax =30mA | R= 60ohm | ||
| Vf = 1.2 Imax= 20mA | R= 190ohm | ||
| Unfortunately when you go and buy a resistor for your LED they are only available in certain values. The values typically available are ( in Ohm) are: 22,,39,47,56 68,100 ,120,150,180,220; so you would have to choose the nearest (e.g.56 or 180 ohm). | |||
| For a really bright effect use LEDs in clusters. LEDs' have an extremely long life and are not too bothered by vibration. They also use very little power and are cold to the touch. | |||
| For model use aim for an LED with at least 5000mcd output (red/green) or 10,000Mcd (white) | |||
| check out: | |||
| http://www.maplin.co.uk/ |
http://www.theledlight.com/technical3.html http://www.kpsec.freeuk.com/components/led.htm
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