Using Your Arduino,

Breadboard and Multimeter

ME 120

Work in teams of two!

Your Multimeter

leads

probes pincer clips – good for working

with breadboard wiring

You will use the multimeter to understand and troubleshoot circuits, mostly

measuring DC voltage, resistance and DC current.

Turn knob to select the

type of measurement.

(push these onto probes)

The Sparkfun Redboard (Uno)

Power can be provided through the USB cable (+5V from

the computer) or externally (7-12V supply recommended)

Measure Vbat

Vbat is the voltage of the battery. It should be over 9V for a new 9V

battery (4.43V was measured when this photo was taken)

• Check the leads are in the

correct sockets: black lead to

COM, and red lead to V

• Connect

• the black probe to the

– terminal of the battery

• the red probe to the

+ probe of the battery.

Measure Vin

Vin is the voltage of the power supply. The USB supplies a nominal 5V

(4.43V was measured when this photo was taken)

Change power source and measure Vin

In this photo, a 7V DC power supply was plugged into the power jack of

the Arduino.

Check Voltage at 5V Power Pin The on-board voltage regulator maintains the voltage on the 5V pin at about 5V

The measured

voltage is close

to 5V target.

Check Voltage at 3.3V Pin The FIDI chip on the Arduino, which helps the microcontroller talk with your computer

through the USB cable, also has an on-board voltage regulator that outputs 3.3V.

If you need less than

5V for a project, you

can use the 3.3V pin,

Which provides about

3.3V. The current

draw from the 3V3 pin

is limited to 50mA.

max power = V∙I

= 3.3V∙0.05A

= 0.165W

= 165mW

Select Resistors Find the 330W and the 10kW resistors from your parts kit .

Now, find the 10kW resistor.

Example: 330W resistor:

3 = orange 3 = orange Add 1 zero to 33 to make 330, so 1 = brown

So, 330 = orange, orange, brown

color digit

black 0

brown 1

red 2

orange 3

yellow 4

green 5

blue 6

violet 7

gray 8

white 9

first

digit

second

digit

number

of zeros

tolerance gold = ±5%

silver = ±20%

Check Resistance of Resistors

Building a circuit on a breadboard

Voltage Drops Around Closed Loops

5V

+

-

Select Resistors Find the 10kW and the 330W resistors from your parts kit.

Now, find the 330W resistor.

Example: 10kW resistor

1 = brown 0 = black Add 3 zeros, so 3 = orange

So, 10kΩ = brown black orange

color digit

black 0

brown 1

red 2

orange 3

yellow 4

green 5

blue 6

violet 7

gray 8

white 9

first

digit

second

digit

number

of zeros

tolerance gold = ±5%

silver = ±20%

13

Build the Series Circuit Below

14

5V

10kW

330W

5V +

-

10kW

330W

All of these circuits are the SAME!!

330W

5V +

-

10kW

Compute Voltage Drops Across the Two Resistors

Use Ohm’s Law: V = I · R

15

Given

Compute the equivalent resistance

Compute the current

Compute the voltage drop across R1

Compute the voltage drop across R2

R1 = 10kΩ R2 = 330 Ω Vb = 5V

Req = _______ Ω

I = _______ A

R1

R2Vb

∆VR1= _______ V

∆VR2= _______ V

Add up the voltage drops across the

resistors with the Negative voltage drop

(the voltage rise) across the battery

∆VR1 + ∆VR2 – ∆Vb = ________

Use Multimeter to Measure Voltages Around Loop

(3) From GND to 5V pin (same +/– direction that was

used across the resistors

(1) Across the 10kΩ resistor

(2) Across the 330Ω resistor

∆Vb = ________

16

5V +

-

10kW

330W

∆VR1 + ∆VR2 – ∆Vb = _______

∆VR1 = _____

∆VR2 = _____

(4) Add up the voltages

Compare Measurements to Theory

17

DVR2 = 0.16V

DVR1 = 4.84V

Vb=5V +

-

R1 = 10kW

R2 = 330W

4.84V + 0.16V – 5.01V = 0.01V

Pretty close!

Kirchoff’s Voltage Law (KVL)

Kirchoff’s Voltage Law says that the algebraic

sum of voltages around any closed loop in a

circuit is zero – we see that this is true for our

circuit. It is also true for very complex circuits.

Notice that the 5V is DIVIDED between the two

resistors, with the larger voltage drop occurring across

the larger resistor. 18

+

-

R1 = 10kW

R2 = 3300W DV = 0.16V

DV = 4.84V

4.84V + 0.16V – 5.01V ≈ 0