Series vs Parallel Circuits

Series Circuits

Components connected end-to-end in a single path:

5V ── [LED1] ── [LED2] ── [LED3] ── [R] ── GND

Properties

• Same current flows through all components
• Voltage divides across each component
• If one fails (open), all stop working
• Total resistance = R1 + R2 + R3 + ...

Example

Three red LEDs in series with a resistor:

• Each LED drops ~2V
• Total drop: 2V + 2V + 2V = 6V (too much for 5V!)
• Two LEDs work: 2V + 2V + 1V(resistor) = 5V ✓

Parallel Circuits

Components connected side-by-side sharing the same two nodes:

5V ──┬── [R1] ── [LED1] ──┬── GND
     ├── [R2] ── [LED2] ──┤
     └── [R3] ── [LED3] ──┘

Properties

• Same voltage across all branches
• Current divides among branches
• If one fails, others keep working
• Total resistance = 1 / (1/R1 + 1/R2 + 1/R3 + ...)

Example

Three LEDs in parallel (each with own resistor):

• Each branch gets 5V
• Each LED has its own current path
• Turning one off doesn't affect others

When to Use Each

| Scenario | Use | |----------|-----| | Multiple LEDs (independent) | Parallel (each with resistor) | | LED + Resistor | Series (always) | | Multiple sensors on I2C | Parallel (shared bus) | | Switches for multiple modes | Can be either |

Key Takeaway

In Arduino projects, you almost always wire LEDs in parallel (each with its own resistor) so they can be controlled independently.