You will need
  • - multimeter (tester);
  • - power source;
To connect the led it is necessary to know its characteristics. Usually LEDs rated at 20 mA, rated voltage depends on the color of the glow. For red and yellow LEDs is 2 V (the valid range is 1.8 - 2.4 V). For white, green and blue 3 In (3 to 3.5 In). When connecting LEDs, it is important to accurately set the quiescent current to 20 mA. In this case, the led will work properly for many years.
Before connecting the led you should pick up a power source. So, if for white, green and blue LEDs two series-connected penlight batteries 1.5 V will give the sum of 3 V, the required voltage must not exceed a maximum value of 3.5 V. But if two batteries on the red or yellow led, it may simply burn out. That is why a responsible approach to the choice of power source, ensure that the voltage at the led is not exceeded.
If the voltage exceeds the required, the circuit should be included a quenching resistor. For example, you want to connect the led 2 to the power supply 9 V. 7 V. it Turns out unnecessary to extinguish them, according to the formula R=U/I you can determine that the desired resistance is equal to 7 V/0,02 A, or 350 Ohms.
Extinguishing the resistor generates heat, so it needs to have the necessary power. Calculate it by the formula P=U*I. Substitute the data: 7 V * 0,02 A = 0,14 W. This means that you need a resistor of about 0.2 W – better take some margin.
When using LEDs it is important in practice to choose the current above 20 mA. To do this, switch the tester to the circuit and check the amperage. If it is a little less than 20 mA, e.g., 17-18, leave him that way. The led will Shine a little less bright, but will last a very long time. If the amperage is much lower or higher, adjust it, changing the resistance of the additional resistor.
Pay attention to the polarity of led, wrong connection may damage it. The anode connects to the positive of power supply, the cathode to minus. From the cathode side of the led bulb is made of a flat area (slice). In addition, the cathode has a shorter output.
If you want to power the led or string of LEDs from AC power, then take care of the DC voltage. In the simplest case, the circuit can include a diode with a breakdown voltage not less than 400 V.