Basic Circuits – Lab 1

XmediaSpring 2011

Basically

• Power– Provides energy for the

sensor and the output

• Sensor– Changes aspects of the

circuit based on input

• Output– Changes based on the

sensor

Solderless Breadboards

• Used to prototype circuit designs

Lighting an LED

• Battery• Resistor• LED

Battery

• Potential Difference - Voltage– Like potential energy

• Positive (VCC, +) and negative (Ground, –)• Note about complete circuits

9 Volts 1.5 Volts

Resistor

• Resistance – Ohms – Ω– Limits the current

LED

• Light Emitting Diode– Directional– Brightness based on current

Lighting an LED

• Build this circuit• Observe the light

turn on when you complete the circuit

Fading and LED

• Battery• Resistor• Potentiometer• LED

Potentiometer

• Variable resistor– Changes the resistance in the circuit

• Positive, negative, and variable legs

Fading an LED

• Build this circuit• Turn the knob• Observe the LED

changing brightness

Some Theory

• Voltage• Resistance• Current• Ohm’s Law• Calculating LED

Resistor Values

Voltage

• V• Potential difference• Energy per unit charge• Drives the current between two points in a

circuit

VDC

V~AC

Current

• I• Flow of unit charge per unit time

– Ampere – Coulombs/second

ADC

A~AC

Resistance

• R, Ω• Opposition to the flow of current

– Based on properties of the material– Conductor vs. Insulator

Ohm’s Law

• Relates voltage, current and resistance

• I = V / R– V = I * R

• Units are important – amperes, ohms, volts– Not milliamps, and

millivolts

Calculating LED Resistor Values• LED Voltage and Current from data sheet

– Typically ~ 1.7V– Typically ~ 20mA

• Know supply voltage – for example 5V• Resistor needs to take the extra voltage

– 5 – 1.7 = 3.3 V

• Ohm’s Law – R = V/I = 3.3V/0.02A = 165Ω

Multimeter Usage

•Connections:–Black - COM / Ground–Red - 10A, 300mA, V/Ohms

•Continuity Test, Diode Test, Resistance, Voltage, Current•Specs:

–DC voltage range: 326mV - 1000V –AC voltage range: 3.26V - 750V –DC/AC current range: 326µA -10A –Resistance range: 326ohm - 32.6Mohm

Mastech MY68Autoranging

Multimeter Usage•Continuity Test

–To check if two points are electrically connected, audible beep sounds if they are

•Diode Test–Diodes only allow current to flow in one direction only, they have a positive (+) lead (i.e. anode) and a negative (-) lead (i.e. cathode)–LEDs are diodes that emit light–You can test the polarity of a diode using a multimeter set to "diode test" mode–Connect the black lead to (-) and the red lead to (+) and the diode will conduct. Connected backwards it will not.

Multimeter Usage•Note: in manual range mode, always make sure to select the correct range before connecting the multimeter leads!!

•Resistance - Ω– Remove component from the circuit

•Voltage - V– At a point in a complete circuit– Connect black lead to ground, red lead to the point in the circuitV

DC

V~AC

Multimeter Usage•Current - A

–Use the 10A jack until you're sure that the current is less than 300mA, and set the range before connecting the leads!–Current is measured in series with the circuit:

• Turn off the power• Break the circuit• Put the meter in series• Turn the power on

ADC

A~AC

Lighting 3 LEDs in Parallel

• Each LED gets its own resistor

• Build this circuit• Measure the voltage

across each branch• Measure the current out

of the battery and before each LED

Current Split - Parallel

• Sum of the current through each branch equals the current from the power source

• Voltages are the same in each branch

• 1/Rtotal = 1/R1 + 1/R2 + … + 1/Rn

Lighting 3 LEDs in Series

• One resistor for all the LEDs

• Build this circuit• Measure the voltage

across each LED• Measure the current out

of the battery and before each LED

Voltage Split - Series

• Voltage across each component is different

• Current through each component is the same

• Rtotal = R1 + R2 + . . . + Rn

Voltage Divider

• Vout = Vin * R2 / (R1 + R2)

• If R1 is variable, as R1 increases Vout decreases

Variable Power Supply

•Output connections in Volts DC (direct current)

–Red: power–Black: ground

•Specifications:–1.5 to 30V DC output0 to 1A output current100 to 240V AC inputOver-voltage/current protectionShort circuit protection