Basic Circuits – Lab 1
Xmedia
Spring 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
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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
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Voltage
Resistance
Current
Ohm’s Law
Calculating LED
Resistor Values
Voltage
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V~
V V
DC
AC
Potential difference
Energy per unit charge
Drives the current between two points in a
circuit
Current
A
A~
• I DC AC
• Flow of unit charge per unit time
– Ampere – Coulombs/second
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 MY68
Autoranging
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
V
DC
V~
AC
– At a point in a complete circuit
– Connect black lead to ground, red lead to the point in the circuit
Multimeter Usage
•Current - A
A
DC
A~
AC
–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:
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Turn off the power
Break the circuit
Put the meter in series
Turn the power on
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 output
0 to 1A output current
100 to 240V AC input
Over-voltage/current protection
Short circuit protection