Building a Common-Emitter Amplifier using an Arduino

Building a Common-Emitter Amplifier using an Arduino | Generated by AI

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Building a Common-Emitter (CE) Amplifier using an Arduino is an interesting project, but it’s worth clarifying the roles: the Arduino itself won’t act as the amplifier (it’s a digital microcontroller), but it can serve as a signal source or measurement tool for a CE amplifier circuit built with a bipolar junction transistor (BJT). A CE amplifier is a classic analog circuit that uses an NPN or PNP transistor to amplify a small input signal, offering moderate voltage gain and current gain.

Here, I’ll guide you through designing a basic NPN-based CE amplifier, using the Arduino to generate an input signal (via PWM) and measure the output. This setup will demonstrate amplification while leveraging Arduino’s capabilities.

Overview of a Common-Emitter Amplifier

Purpose: Amplifies a small AC signal (e.g., audio or a sine wave).
Key Features:
- Transistor operates in the active region.
- Input signal applied to the base, output taken from the collector.
- Voltage gain determined by resistor ratios and transistor properties.
Components:
- NPN transistor (e.g., 2N3904 or BC547)
- Resistors (for biasing and load)
- Capacitors (for coupling AC signals)
- Arduino (signal source and measurement)

Step 1: Design the Circuit

Components Needed

NPN transistor (e.g., 2N3904)
Resistors: R1 = 47kΩ, R2 = 10kΩ (biasing), RC = 1kΩ (collector), RE = 220Ω (emitter)
Capacitors: C1 = 10µF (input coupling), C2 = 10µF (output coupling), CE = 100µF (emitter bypass, optional for higher gain)
Arduino (e.g., Uno)
Breadboard, jumper wires
Power supply (Arduino’s 5V pin or external 9V, adjusted as needed)

Circuit Schematic

Vcc (5V) ---- R1 ----+---- RC ---- Collector (C)
             47kΩ     |     1kΩ          |
                      |                  |
Base (B) --- C1 -----+                  |
            10µF     |                  |
Arduino PWM (Pin 9)  R2                 |
                     10kΩ              Output --- C2 ---- To Arduino A0
                      |                  |         10µF
                      |                  |
                      +---- RE ---- Emitter (E) --- CE (optional) --- GND
                           220Ω                   100µF
                      |
                     GND

Biasing (R1, R2): Sets the transistor’s operating point.
RC: Collector resistor for output signal.
RE: Emitter resistor for stability.
C1, C2: Block DC, pass AC signals.
CE (optional): Bypasses RE for higher AC gain.

Operating Point

Goal: Bias the transistor in the active region (e.g., VCE ≈ 2.5V for 5V supply).
Voltage divider (R1, R2): ( V_B = V_{CC} \cdot \frac{R2}{R1 + R2} = 5 \cdot \frac{10k}{47k + 10k} \approx 0.88V ).
( V_E = V_B - V_{BE} \approx 0.88 - 0.7 = 0.18V ).
( I_E = \frac{V_E}{RE} = \frac{0.18}{220} \approx 0.82 \, \text{mA} ).
( V_C = V_{CC} - I_C \cdot RC \approx 5 - 0.82 \cdot 1k \approx 4.18V ).
( V_{CE} = V_C - V_E \approx 4.18 - 0.18 = 4V ) (good for 5V supply).

Step 2: Use Arduino as Signal Source

Arduino’s Role

Generate a small AC signal using PWM (Pulse Width Modulation) on a pin like 9 (which supports PWM).
Filter the PWM to approximate a sine wave with a simple RC low-pass filter (optional).

Code to Generate a Signal

const int pwmPin = 9; // PWM output pin

void setup() {
  pinMode(pwmPin, OUTPUT);
  // Set PWM frequency (optional, default is ~490 Hz)
}

void loop() {
  // Simulate a sine wave with PWM (0-255 range)
  for (int i = 0; i < 360; i += 10) {
    float sineValue = sin(radians(i)); // Sine wave from -1 to 1
    int pwmValue = 127 + 127 * sineValue; // Scale to 0-255
    analogWrite(pwmPin, pwmValue);
    delay(10); // Adjust for frequency (e.g., ~100 Hz here)
  }
}

Output: ~0–5V PWM signal, centered at 2.5V with ~2.5V peak-to-peak.
C1: Removes the DC offset, passing only the AC component (~1.25V peak) to the base.

Optional Filter

Add a 1kΩ resistor and 0.1µF capacitor in series from Pin 9 to GND, tapping the signal before C1, to smooth PWM into a rough sine wave.

Step 3: Measure the Output

Arduino Measurement

Connect the amplifier output (after C2) to A0.
Use the Arduino to read the amplified signal and display it via Serial Monitor.

Code to Measure and Display

const int inputPin = A0; // Measure output here

void setup() {
  Serial.begin(9600);
}

void loop() {
  int sensorValue = analogRead(inputPin); // 0-1023 maps to 0-5V
  float voltage = sensorValue * (5.0 / 1023.0);
  Serial.print("Output Voltage (V): ");
  Serial.println(voltage);
  delay(100); // Adjust sampling rate
}

Expected Gain

Voltage gain ( A_v = -\frac{RC}{RE} = -\frac{1k}{220} \approx -4.5 ) (negative due to phase inversion).
Input: ~1.25V peak (after coupling).
Output: ~4.5 × 1.25 = 5.625V peak (but clipped at 5V due to supply limit).

Step 4: Build and Test

Assembly

Wire the circuit on a breadboard as per the schematic.
Upload the signal generation code to Arduino and connect Pin 9 to C1.
Power the circuit via 5V from Arduino (or use 9V with adjusted resistors).
Upload the measurement code and open Serial Monitor (9600 baud).

Verification

Input Signal: ~1–2V peak-to-peak after C1 (use a multimeter or oscilloscope if available).
Output Signal: Should be larger (e.g., 4–5V peak-to-peak) and inverted.
Check VCE (~2–4V) with a multimeter to ensure active region operation.

Tips and Troubleshooting

Gain Too Low: Add CE (100µF) across RE to boost AC gain (removes RE’s degeneration).
Clipping: If output exceeds 5V, reduce input amplitude (adjust PWM range) or increase Vcc (e.g., 9V external supply).
Noise: PWM is square-ish; a better sine wave (via external generator or filter) improves results.
Transistor Specs: Ensure 2N3904 handles currents (Ic < 200mA, safe here).

This setup demonstrates a CE amplifier’s core behavior—voltage amplification—while integrating Arduino for signal generation and analysis. Want to tweak the gain, add a speaker for audio, or refine the signal? Let me know!

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