User Manual
11
When the potentiometer is used as a rheostat, connect the middle pin and one of the
other 2 pins in the circuit. Thus you can get a smoothly and continuously changed
resistance value within the travel of the mov ing contact.
3. Serving as a current controller
When the potentiometer acts as a current controller, the sliding contact terminal must be
connected as one of the output terminals.
LED
Semiconductor light-emitting diode is a type of component w hich can turn electric energy
into light energy via PN junctions. By wavelength, it can be categorized into laser diode,
infrared light-emitting diode and visible light-emitting diode which is usually know n as light-
emitting diode (LED).
(k) (l)
See LED in figure (k). Figure (l) is the circuit symbol. Diode has unidirectional conductiv ity, so
the current flow w ill be as the arrow indicates in figure (l). You can only prov ide the anode
with a positiv e power and the cathode with a negative. Thus the LED will light up.
In this kit, LEDs of red, green, yellow and w hite are provided. An LED has two pins. The longer
one is the anode, and shorter one, the cathode. Pay attention not to connect them inversely.
There is fixed forward voltage drop in the LED, so it cannot be connected with the circuit
directly because the supply v oltage can outweigh this drop and cause the LED to be burnt.
The forward voltage of the red, yellow, and green LED is 1.8 V and that of the white one is
2.6 V. Most LEDs can withstand a maximum current of 20 mA, so we need to connect a
current limiting resistor in series.
The formula of the resistance value is as follows:
R = (V
supply
– V
D
)/I
R stands for the resistance v alue of the current limiting resistor, Vsupply for v oltage supply, VD
for voltage drop and I for the working current of the LED.
If we provide 5 voltage for the red LED, the minimum resistance of the current limiting resistor
should be: (5V-1.8v )/20mA = 160Ω. Therefore, you need a 160Ω or larger resistor to protect
the LED. You are recommended to use the 220Ω resistor offered in the kit.
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