An introduction to basic circuit design, given at RobotsConf 2014.

1. So You Want to Build a Circuit?
Bryan Hughes, Ph.D.
@nebrius
Frontend Dev at Rdio

2. Voltage and Current
Voltage is the potential difference
between two points, and current is the
flow rate of electrons between them
-
e-e-e-
+

3. Basic Components
• Resistor
• Capacitor
• Inductor
• Battery
• Diode
• LED
• VCC
• GND

4. Ohm’s Law
V = I · R
V = I · R (1)
V = voltage (V)
I = current (A)
R = resistance (⌦)
P = V · I =
V 2
R
Resistor: Battery: Ground:
V1 = V ·
R1
(2)
P = V · I =
V 2
R
(3)

6. V = I · R (1)
V = voltage (V)
I Power = V current = I Usage
· R
(A)
R = resistance (⌦)
P = V · I =
V 2
R
V1 = V ·
R1
R1 + R2
Resistor: Battery: Ground:
I = V ·
R1 · R2
(2)
P = V · I =
V 2
R
(3)
P = power(W) (4)
V1 = V ·
R1
R1 + R2
(5)

7. V = I · R
P = V · I =
V 2
R
Series Resistors
V1 = V ·
R1
R1 + R2
I = V ·
R1 · R2
R1 + R2
R =
V Vdrop
Resistor: Battery: Ground:

8. P = V · I =
V 2
R
V1 = V ·
R1
R1 + R2
Parallel Resistors
I = V ·
R1 · R2
R1 + R2
R =
V Vdrop
Iideal
Resistor: Battery: Ground:

9. · R
V1 = V ·
R1
R1 + R2
I = V ·
R1 · R2
R1 + R2
Light Emitting Diodes
R =
V VLED
I
Resistor: LED: Battery: Ground:

10. Voltage
5
4
3
2
1
0
Voltage Low Threshold High Threshold
Time
Digital Logic
Low: -0.5V to 0.2⋅Vcc
High: 0.7⋅Vcc to Vcc + 0.5V

11. Switches
Pull Down Resistors stabilize the
voltage while the switch is open

12. Relays
Software controllable switches

13. Transistors
At the heart of almost every signal
conversion circuit, such as power
boosting and voltage level shifting

14. Power concerns
• Everything has power limits
• Exceeding those limits == damage
• Microcontrollers have low limits
• Key to great hardware is making everything happy

15. Thank You
Bryan Hughes
@nebrius