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Author Topic: Measuring Voltage across LED with Multimeter  (Read 847 times)
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When measuring voltage across an LED with a multimeter, do I put the setting to DCV 200?  I'm using a 220 ohm resistor in the circuit.  When doing so I get a reading of 1.7.  To me that sounds like the voltage the LED is using. smiley-eek-blue
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When measuring voltage across an LED with a multimeter, do I put the setting to DCV 200?  I'm using a 220 ohm resistor in the circuit.  When doing so I get a reading of 1.7.  To me that sounds like the voltage the LED is using. smiley-eek-blue

Yes, 1.7vdc DC is the voltage drop across the diode, however it's the current flow that is creating the light emitted. Operating Leds is mostly all about current, their forward voltage drop Vf just tells you the minimum voltage they need to operate at. The voltage drop across the resistor is what is controlling the current flow amount through the led.
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Ok!  What does setting the multimeter to 20 DCV or 200 DCV mean?
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do I put the setting to DCV 200?
You can get a more accurate reading if you set your meter onto DCV20 or even DCV2, the number is the maximum voltage you can read so with DCV200 you can go up to 200V. By droping down to DCV20 you get an extra decimal place of accuracy, down to DCV2 you get two extra places.
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Ok!  What does setting the multimeter to 20 DCV or 200 DCV mean?

That sets what voltage range the meter will utilize in displaying the value. Most meters today also have a auto voltage range option, but I don't know what specific meter you are using and how many digits it uses in it's display. But if you have a 1.7vdc signal being measured by a typical '3 1/2 digit' meter, if it's in the 20DC range it will display as 1.700 if it's a 3 1/2 digit meter and will display 1.7 if it's turned to the 200DCV range.
So set to 20DCV, means the meter can display from 0000 to 1.999 volts DC and if on the  200DCV range it can display 0000 to 199.9 volts DC. Any voltage higher then these in those ranges will display 'over range' in whatever manner your specific meter uses to signal the user of that situation. If your meter has a auto-range function then it will read the voltage and use the range that allows the value to be displayed using the best resolution in can to display it.

Lefty
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