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Circuit and sensors

This page outlines the electronic systems used for the laser, including all circuits and sensors used.

Info

For the research that went into designing the systems, please see the circuit research page.

Electron Beam Control Subsystem

These circuits use BSP89 N-Channel MOSFETs to interface the 5V logic of the Arduino with high-voltage or high-current power sources.

  1. Beam Enable (Digital Switch)
    • Purpose: Provides a master hardware enable/disable for the electron beam.
    • Input: PinD8 (Digital Output).
    • Key Components:
      • M1 (BSP89): Serves as the low-side switch.
      • R1 (10 kΩ): Pull-down resistor to ensure the beam remains OFF if the Arduino pin is floating or during boot-up.
    • Operation: Driving PinD8 HIGH completes the circuit from NegativePowerSource to Ground.
  2. Beam Modulation (PWM)
    • Purpose: Controls beam intensity or pulse frequency.
    • Input: PinD9 (PWM capable).
    • Key Components:
      • R1 (100 Ω): Gate resistor to limit inrush current and dampen oscillations during high-frequency switching.
      • R2 (10 kΩ): Safety pull-down resistor.
    • Design Note: The addition of the gate resistor (R1) makes this circuit more suitable for the rapid switching required in PWM modulation compared to the Enable circuit.

Monitoring & Diagnostic Subsystem

These circuits provide real-time feedback to the Arduino for safety and data logging.

  1. High-Voltage Voltmeter (Voltage Divider)
    • Purpose: Scales a 20kV source down to a range readable by the Arduino (0V–5V).
    • Circuit Topology: A high-impedance voltage divider.
    • Series Resistance (\(R_{top}\)): Four 5 MΩ resistors in series (20 MΩ total) to minimize current draw and power dissipation.
    • Parallel Resistance (\(R_{bottom}\)): Four 20 kΩ resistors in parallel (5 kΩ total).
    • Calculated Output: \(V_{out} = V_{in} \cdot \frac{R_{parallel}}{R_{series} + R_{parallel}}\).
    • For 20kV input, \(V_out = 20,000 \times (5,000)/(20,000 \times 5,000) \approx \text{4.99 V}\)
  2. Thermistor Temperature Sensor
    • Purpose: Monitors component or environment temperature using a 10k NTC thermistor.
    • Topology: Voltage divider with a 10kΩ fixed resistor (R2).
    • Firmware Logic: The output at PinA0 follows the Steinhart-Hart model (or the simplified Beta parameter equation provided in your LTspice params) to convert voltage to Celsius.
  3. 9V Logic Level Converter (Voltage Divider)
    • Purpose: Scales a 9V power source down to a safe ~3.3V reference voltage for logic-level applications.Circuit
    • Topology: A standard single-path series voltage divider.
    • Series Resistance (\(R_{top}\)): A single 10 kΩ resistor connected to the 9V source.
    • Parallel Resistance (\(R_{bottom}\)): A 4.7 kΩ and a 1 kΩ resistor wired in series to create a 5.7 kΩ total resistance to ground.
    • Calculated Output: \(V_{out} = V_{in} \cdot \frac{R_{bottom}}{R_{top} + R_{bottom}}\)
    • For a 9V input: \(V_out = \text{9 V} \times 5700/(10000 + 5700) \approx \text{3.27 V}\).

Physical Hardware Integration

  • Based on the current assembly:
    • Microcontroller: Arduino Uno R3.
    • Primary Environmental Sensor: DHT11 (Digital Temperature & Humidity).
    • Wiring: VCC (Red), GND (Black), Data (Green/Yellow).
    • Status Indicator: LED Circuit on PinD13.
    • Resistor: 330 Ω to limit current to approximately 9mA (well within the Uno's 20mA pin limit).

Build Team Action Items

  • Soldering: Transition the PWM and Enable circuits from breadboards to perma-proto boards to handle the NegativePowerSource current safely.
  • Safety Check: Verify that the 5 MΩ resistors in the Voltmeter circuit are rated for high-voltage (e.g., 5kV+ each) to prevent arcing across the resistor bodies.
  • Cable Management: Use the wire strippers seen in your setup to create clean, crimped connections for the DHT11 and MOSFET gates to prevent accidental shorts.