SNVAA20 July   2021 DRV8833 , DRV8833 , LMR33630 , LMR33630

 

  1.   Trademarks
  2. 1Introduction
  3. 2Motorized Resistive Load Architecture
    1. 2.1 Controller Board
    2. 2.2 Resistor Plate
  4. 3Motorized Resistive Load Design
    1. 3.1 Controller Board Design
      1. 3.1.1 Power Management
      2. 3.1.2 Power Converter Selection
      3. 3.1.3 Interface and ADC Selection
    2. 3.2 Resistor Plate Design
      1. 3.2.1 Motor and Motor Driver Selection
      2. 3.2.2 Resistor Track
      3. 3.2.3 Mechanical Arm Assembly
      4. 3.2.4 Feedback Control
  5. 4Thermal Considerations
  6. 5Performance and Results
  7. 6Summary
  8. 7Appendix
    1. 7.1 Controller Board Main Schematic
    2. 7.2 Controller Board Sub-Schematics
    3. 7.3 Resistor Plate Schematics
    4. 7.4 Python Code

2.1 Controller Board

The controller PCB is a 4-layer board that houses the user interface, handles the power management and sends the motor drive signals to the stepper motor located on the resistive load PCB. The Raspberry Pi 4 model B was used for this design and it mates with the controller board via the general-purpose input output (GPIO) pin header via a connector that is used as a spacer. The 4079 from Adafruit Industries is a suitable female-to-male 2 × 20 position connector with a 0.100 in pin pitch. Each pin on this connector is rated for 3 A which meets the requirements of this design. The Raspberry Pi is typically powered from a designated USB Type-C® port. The controller PCB eliminates the need to use the USB Type-C port by back-powering the Raspberry Pi via the power pins (pins 2 and 4) on the GPIO header of the Raspberry PI. Power comes in through a barrel connector and passes through the reverse-polarity protection provided by LM74610-Q1. Power then continues to feed into two buck converters, a pair of LMR33630 devices. The first buck converter provides power to the motor driver DRV8833. The second buck converter powers the Raspberry Pi with 5 V and a low-dropout regulator (LDO), the LP2980-ADJ which then provides a quiet 3.3-V power rail for the two ADC121C021 analog-to-digital converters (ADCs). The LDO also provides a reference voltage for the potentiometer that is used to determine the target resistance selected by the user, in addition to providing power to the LCD screen. The backlight of the LCD screen, however, is powered by a 3.3-V rail provided by the Raspberry Pi.

Figure 2-2 Controller Board