So You Want to Build a Circuit?Bryan Hughes, Ph.D.

@nebrius Frontend Dev at Rdio

Voltage and CurrentVoltage is the potential difference

between two points, and current is the flow rate of electrons between them

-

e-

e-

e-

+

Basic Components

• Resistor

• Capacitor

• Inductor

• Battery

• Diode

• LED

• VCC

• GND

(1) V = I ·R

(2) P = V · I =

V 2

RSeries resistors

(3) V1 = V · R1

R1 +R2

Parallel resistors

(4) I = V · R1 ·R2

R1 +R2

LED resistor

(5) R =

V � Vdrop

Iideal

1

Ohm’s Law

Resistor: Battery: Ground:

V = I ·R (1)

V = voltage (V)

I = current (A)

R = resistance (⌦)

(2)

P = V · I =

V 2

R(3)

P = power (W)

(4)

Series resistors

V1 = V · R1

R1 +R2(5)

Parallel resistors

I = V · R1 ·R2

R1 +R2(6)

LED resistor

R =

V � VLED

I(7)

1

(1) V = I ·R

(2) P = V · I =

V 2

RSeries resistors

(3) V1 = V · R1

R1 +R2

Parallel resistors

(4) I = V · R1 ·R2

R1 +R2

LED resistor

(5) R =

V � Vdrop

Iideal

1

Power Usage

Resistor: Battery: Ground:

V = I ·R (1)

V = voltage (V)

I = current (A)

R = resistance (⌦)

(2)

P = V · I =

V 2

R(3)

P = power (W)

(4)

Series resistors

V1 = V · R1

R1 +R2(5)

Parallel resistors

I = V · R1 ·R2

R1 +R2(6)

LED resistor

R =

V � VLED

I(7)

1

(1) V = I ·R

(2) P = V · I =

V 2

RSeries resistors

(3) V1 = V · R1

R1 +R2

Parallel resistors

(4) I = V · R1 ·R2

R1 +R2

LED resistor

(5) R =

V � Vdrop

Iideal

1

Series Resistors

Resistor: Battery: Ground:

(1) V = I ·R

(2) P = V · I =

V 2

RSeries resistors

(3) V1 = V · R1

R1 +R2

Parallel resistors

(4) I = V · R1 ·R2

R1 +R2

LED resistor

(5) R =

V � Vdrop

Iideal

1

Parallel Resistors

Resistor: Battery: Ground:

Light Emitting Diodes

(1) V = I ·R

(2) P = V · I =

V 2

RSeries resistors

(3) V1 = V · R1

R1 +R2

Parallel resistors

(4) I = V · R1 ·R2

R1 +R2

LED resistor

(5) R =

V � VLED

I

1

Resistor: Battery: Ground:LED:

Volta

ge

0

1

2

3

4

5

Time

Voltage Low Threshold High Threshold

Digital LogicLow: -0.5V to 0.2⋅Vcc

High: 0.7⋅Vcc to Vcc + 0.5V

SwitchesPull Down Resistors stabilize the voltage while the switch is open

RelaysSoftware controllable switches

TransistorsAt the heart of almost every signal conversion circuit, such as power boosting and voltage level shifting

Power concerns

• Everything has power limits

• Exceeding those limits == damage

• Microcontrollers have low limits

• Key to great hardware is making everything happy

Thank YouBryan Hughes

@nebrius