Key Components on the Bodytech PCB

🔋 1. Power Supply & Boost Converter Stage

• Battery:
  +HD724460PLV, 2650mAh, 3.8V LiPo

  • This battery provides a stable energy source for the EMS output. Capacity and current delivery are sufficient for multi-channel operation.

• Boost Converter Circuit:

  • Inductor (≈150 µH) – core component that defines energy transfer quality. Affects pulse strength and ripple.

  • Boost IC (e.g., MT3608 or equivalent) – converts 3.8V input to 50–100V required for EMS output.

  • High-speed Schottky Diode – enables efficient and fast switching in boost operation.

  • Input/Output Capacitors – filter out voltage ripple and stabilize high-voltage output.

✅ Why it matters: A clean, stable high-voltage rail is critical to generate strong, non-distorted impulses for muscle contraction.

⚡ 2. Output Driver Stage (Per Channel)

• MOSFETs (N-channel or half-bridge setup):

  • Controls the ON/OFF state of each impulse with precision.

  • Must be fast-switching, low RDS(on), and thermally stable.

• Gate Drivers (optional):

  • Improve MOSFET switching behavior and impulse sharpness.

• Snubber Circuits / Output Capacitors:

  • Absorb voltage spikes, reduce overshoot, and smooth out pulse transitions.

✅ Why it matters: Output drivers define the impulse shape, speed, and force. Quality components here ensure reliable stimulation without signal distortion or channel leakage.

🧠 4. MCU & PWM Control

• MCU (ESP32-S3):

  • Sends precise PWM signals to each output channel.

  • Controls pulse width, frequency, rise/fall time, and training duration.

✅ Why it matters: PWM logic must be clean, consistent, and adjustable based on workout modes. Firmware stability plays a major role.

✅ Summary: Top Priority Components for Signal Quality

Display requirements, Button & positioning

Monochrome OLED Display:

1. Simple Icons (Bluetooth, Battery):

   • Typical of low-power OLED displays used in IoT and wearable devices.

2. Black background with white or greenish icons:

   • Matches the appearance of OLED, which emits light only where needed.

3. Compact size and position:

   • Fits perfectly into small housings like your EMS eBox device.

4. Low power consumption:

   • Ideal for battery-powered devices using a 3.8V 2650mAh LiPo cell.

5. Easy integration with ESP32-S3:

   • These displays communicate via I²C (2 wires) or SPI (4 wires) and are fully supported by libraries like U8g2or Adafruit_SSD1306.

Recommended Display Module:

• Model: SSD1306 or SH1106 (commonly used)

• Size: 0.66″ or 0.91″ OLED

• Color: White/Green on Black

• Resolution: Typically 64×48 or 128×32 pixels

• Interface: I²C (SDA/SCL) or SPI

• Voltage: 3.3V compatible

On/Off Button

• High Quality Apple iPhone Style

Why OLED and not LCD or e-Paper?

PCB Dimensions