# Capacitor
## What is Capacitor
Capacitor is an electronic component that can store electric charge, with the characteristic of blocking DC and passing AC. Commonly used in filtering, timing, and energy storage circuits.
### Capacitor Features
- **Store Charge**: Can store electrical energy
- **Block DC, Pass AC**: Blocks DC current, allows AC current
- **Filtering Effect**: Can filter noise in circuits
- **Timing Function**: Works with resistors to control time constants
## Capacitor Types
### Ceramic Capacitor (Monolithic)
- **Features**: **Non-polarized** (no need to distinguish positive/negative), small size, good stability
- **Capacitance**: 22pf, 100nf (0.1μF)
- **Applications**: High-frequency filtering, decoupling, timing circuits
**Important**: Ceramic capacitors **have no polarity**, can be connected in any direction, will not be damaged.
### Electrolytic Capacitor
- **Features**: Polarized, large capacitance
- **Capacitance**: 10μF, 100μF
- **Applications**: Power supply filtering, energy storage, low-frequency filtering
## Capacitor Parameter Description
Main parameters marked on capacitors:
### Capacitance Value
- **Ceramic Capacitor**: 22pF, 100nF (0.1μF), etc.
- **Electrolytic Capacitor**: 10μF, 100μF, etc.
- **Digital Marking Method**: 104 = 0.1μF (first two digits are significant figures, third digit is multiplier)
### Voltage Rating
- **16V, 25V, 50V**, etc.: Indicates maximum working voltage
- **Selection Principle**: Voltage rating should be at least 1.5-2 times the working voltage (e.g., 5V circuit choose 16V)
### Polarity Marking (Electrolytic Capacitor)
Electrolytic capacitors are marked with polarity:
- **+** or **positive symbol**: Indicates anode, connect to power positive
- **-** or **negative symbol**: Indicates cathode, connect to power negative
- **Long pin**: Usually anode
- **Short pin**: Usually cathode
## Polarity Identification
### Ceramic Capacitor (Non-polarized)
**Ceramic capacitors do not need to distinguish positive/negative**:
- Both pins are identical, can be connected in any direction
- Reversed connection won't damage or affect function
- Easy to use, suitable for beginners
### Electrolytic Capacitor (Polarized)
Electrolytic capacitors **must be connected with correct polarity**, reversed connection will cause capacitor damage or explosion!
#### Identification Method
- **Anode**: Long pin, marked with `+` or positive symbol
- **Cathode**: Short pin, marked with `-` or negative symbol
**Memory tip**: Long pin is positive (+), short pin is negative (-)
#### Why Must Polarity Be Distinguished?
Electrolytic capacitors contain electrolyte inside. Reversed connection causes internal chemical reaction, producing gas, which may cause explosion or damage.
## Working Principle
### Capacitor Functions
1. **Store Charge**: Stores electrical energy when charging, releases electrical energy when discharging
2. **Filtering**: Filters high-frequency noise in circuits
3. **Decoupling**: Provides instantaneous large current for IC chips
4. **Timing**: Works with resistors to control charge/discharge time
### Capacitance Units
- **Farad (F)**: Basic unit, but too large, not commonly used
- **Microfarad (μF)**: 1μF = 0.000001F, commonly used unit
- **Nanofarad (nF)**: 1nF = 0.001μF
- **Picofarad (pF)**: 1pF = 0.001nF, small capacitance unit
## Connection Method
### Power Filtering Circuit (Complete Circuit)
### Connection Instructions
**Complete Circuit Connection**:
- VCC (5V) → LED → 220Ω resistor → GND (load circuit)
- Electrolytic capacitor (10μF or 100μF) connected in parallel across power supply, anode to VCC, cathode to GND
- Ceramic capacitor (100nF) connected in parallel across power supply, one end to VCC, one end to GND
**Power Filtering Effect**:
- **Electrolytic Capacitor**: Filters low-frequency noise in power supply, stabilizes power supply voltage
- **Ceramic Capacitor**: Filters high-frequency noise, provides instantaneous large current
- Two capacitors used together can better stabilize power supply, LED will emit light stably
**Note**:
- **Electrolytic capacitors are polarized**, must be connected correctly (anode to VCC, cathode to GND), reversed connection will damage
- **Ceramic capacitors are non-polarized**, can be connected in any direction, will not be damaged
- Large capacitance capacitors (electrolytic) for low-frequency filtering, small capacitance capacitors (ceramic) for high-frequency filtering
## Arduino Example Code
### Example: LED Blink (Using Capacitor Delay)
```cpp
const int ledPin = 13;
const int buttonPin = 2;
void setup() {
pinMode(ledPin, OUTPUT);
pinMode(buttonPin, INPUT_PULLUP);
}
void loop() {
if (digitalRead(buttonPin) == LOW) {
digitalWrite(ledPin, HIGH);
delay(100); // Capacitor can extend this delay effect
digitalWrite(ledPin, LOW);
}
}
```
**Explanation**: In practical applications, capacitors are usually used for hardware filtering, software delay uses `delay()` function.
## Common Questions and Answers
### Q1: Do Ceramic Capacitors Need to Distinguish Polarity?
**No**! Ceramic capacitors are **non-polarized**:
- Both pins are identical, can be connected in any direction
- Reversed connection won't damage or affect function
- Very convenient to use, no need to worry about wrong connection
### Q2: What If Electrolytic Capacitor is Reversed?
- **Immediately disconnect power**, check if capacitor is damaged
- If capacitor is bulging, leaking, or smoking, must replace
- Reversed connection may cause capacitor explosion, very dangerous
### Q3: How to Choose Capacitor Capacitance?
- **Power Filtering**: Use large capacitance electrolytic capacitors (10μF - 1000μF)
- **Decoupling**: Use small capacitance ceramic capacitors (100nF)
- **Timing Circuits**: Calculate according to time constant: τ = R × C
### Q4: Can Capacitors Be Connected in Series or Parallel?
- **Parallel**: Capacitance adds up, total capacitance = C1 + C2 + C3...
- **Series**: Reciprocal of capacitance adds up, total capacitance = 1/(1/C1 + 1/C2 + ...)
- Electrolytic capacitors in series need to pay attention to voltage distribution
## Safety Precautions
⚠️ **Important Notes**:
- **Electrolytic capacitors must be connected with correct polarity**, reversed connection may explode
- Do not exceed maximum working voltage
- Large capacitance capacitors may still have charge after power off, be careful
- Damaged capacitors (bulging, leaking) must be replaced immediately
## Practical Applications
Capacitors are commonly used for power filtering, decoupling, timing circuits, signal coupling, etc. In Arduino projects, mainly used to stabilize power supply voltage and reduce noise interference.
