PAGE 045 OF 150 · POWERING LEDS
Measuring LED Current with a Multimeter
Place the meter in series with the LED to read current.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
The method
To measure current, the meter must be in series with the LED so all current passes through it.
- Switch the meter to the mA range and move the red lead to the mA socket.
- Break the circuit, for example by lifting one leg of the resistor.
- Connect the meter between the break so current flows through it.
- Read the display, then restore the lead and range.
Cautions
Never connect the meter across a supply in current mode, because it is almost a short circuit and can blow its fuse.
Alternative
Measure the voltage across the resistor and divide by its value. For 3 V across 330 ohms, current is about 9.1 mA.
REMEMBER
The resistor sets the current, so the resistor sets the safety.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
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