# Analog Discovery - Ohm's Law

## Project 1: Resistors

In this experiment, we will use Digilent's Analog Discovery and a digital multimeter to explore a fundamental equation used in electric circuit analysis and design: Ohm's Law. Ohm's law describes the relationship between the voltage across a resistor and the resulting current passing through the resistor. The links in the related material section provide more detail regarding these topics.

Ohm's law states that the voltage across a resistor and the current through the resistor are proportional to one another. The constant of proportionality is the resistance. There are three variations of Ohm's Law in equation form:

$$v = i \cdot R$$ $$i = \frac{v}{R}$$ $$R = \frac{v}{i}$$

## Prerequisites

• Be able to use the Analog Discovery's voltage instrument and AWG to provide constant (DC) voltages.
• Be able to measure voltage using a voltmeter.
• Be able to measure current using an ammeter.

### Inventory

• 1 Digital multimeter
• 1 A resistor with red as the third color band (They will be in the 1kΩ to 9.9kΩ range)
• 2 Analog Discovery pins

## A. Circuit Schematic

1. Use V+ to apply 5V across the resistor.
2. Use the DMM in series with the resistor in the circuit to measure the current.
3. Use channel 1 (1+ and 1-) to measure the voltage difference (VOUT) across the resistor.

## B. Create Circuit

1. Connect V+ (red wire) to one removable pin.
2. In a different row, connect the other removable pin to the resistor.
3. Connect 1+ (orange wire) and 1- (orange and white striped wire) across the resistor, with 1+ on the side closest to V+.
4. Connect ground (, black wire) to the resistor.
• Note: The removable pins are where the leads of the DMM will be connected.

## A. Open Voltmeter Instrument

1. Open WaveForms™ to view main window.
2. Click on the More Instruments dropdown menu to open the Voltmeter instrument.
• Note: The Voltmeter instrument will allow us to measure the voltage difference (VOUT) across the resistor.

## B. Open Voltage Instrument

2. Click on the Voltage icon to open the Power Supplies instrument.

## C. Turn on Power

• Channel 1 on the Voltmeter instrument will not show a voltage difference across the resistor since the DMM is not connected to the removable pins yet.

## A. Collect Data

1. Set the DMM to measure milliamperes (mA). Connect it to the circuit by pressing the red lead to the removable pin connected to V+. The black lead (COM) should be pressed to the other removable pin.
2. Record the current value measured on the DMM as well as the voltage value measured on Channel 1 of the Voltmeter instrument.

## B. Analyze Data

1. Use the equations provided in the introduction to this project and the values you measured in Part A to estimate the resistance of the resistor you chose for your experiment. Record this resistance value.

## C. Compare with Expectations

1. Use the color bands on the resistor to determine its nominal resistance. Calculate a percent difference between the value calculated in Part B and the expected value determined from the color bands. Percent difference is calculated as:

$$\% {\rm{ Error = }}\left| {\left. {\frac{{Measured - Expected}}{{Expected}}} \right|} \right. \times 100$$

Is the difference within the range you would expect based on the tolerance color band of the resistor?