Hi, I'm a student and I can't seem to figure out how to make a circuit with a diode 1N4007, led, and resistor of 75 ohm. I have to make this circuit so I can measure the voltage and ampere through the led.
Can't you ask your supervisor/instructor/prof?
And get them to explain what "DO NOT CREATE TOPICS IN THIS CATEGORY" means.
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How are the three components and the power source connected?
What is the voltage of the power source?
That's easy. No voltage and no amperes, because there is no voltage source in your circuit. No Arduino needed.
If you plan to use a 5V source, then that could be a problem, since over 40 milliamps could flow, which might damage the led. Most LEDs have a maximum of 20 or 30mA and could have a forward voltage as low as around 1.8V (assuming it is a visible led, not IR). Red LEDs have a forward voltage around 1.8 to 2V.
If you use a 3.3V source, then this would be ok for LEDs with a forward voltage of below about 3V, but for LEDs with a forward voltage close to 3.3V, they might not light up. Blue and white LEDs can have a forward voltage of about 3 to 3.2V.
So lets assume it's a red led and you use a 3.3V source. (Some models of Arduino cannot supply much current from their 3.3V pins, so let's assume you are either not using one of those types of Arduino, or you are using an external 3.3V supply).
You could connect one of the Arduino analog pins to the junction between the led cathode and the 75R resistor, and that the other end of the resistor is connected to ground and the led anode is connected to 3.3V.
If your code reads around 310 from the analog input. This would indicate that the voltage across the resistor is around 5.0*310/1023 = 1.5V (assuming this is a 5V Arduino). So the voltage across the led must be (3.3 - 1.5) = 1.8V. The current flowing through both the resistor and led must be 1.5 / 75 = 20mA
What is the purpose of the diode in the circuit?
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Hi, @bwnh
Welcome to the forum.
Were you given a question sheet explaining what is required?
If so can you post the text here?
What voltage is recommended to do your testing at?
Thanks.. Tom.. 
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