You Will Need

CHAPTER 4: LEDs 67

(a) (b)

(c)

Set the variable resistor to its middle point and wire up the breadboard as shown in Figure 4-15b. You will probably have to move the positive lead of your multimeter to a different socket when measuring current. Select a current range of 200mA DC. Now adjust the variable resistor until the current reads 20mA.

We can now measure the voltage across the LED. To do this, first disconnect the multimeter, put the positive multimeter back in the right socket for measuring voltage, and then change the range to 20V DC. Wire it up as shown in Figure 4-15c and measure the voltage. In this case, it was 1.98V.

Figure 4-15 Measuring the forward voltage of an LED

You Will Need

Quantity Names Item

Appendix Code 1 Solderless breadboard T5 1 D1 LED K1 3 R1 500Ω trimpot R3 Jumper wires T6

1 1 4 4 × AA battery holder H1 Battery clip H2 AA batteries