Wall-E-2027-Board-Design

SRA Board

The SRA board is a development board based on ESP32 with on-board peripherals like a programmable LED matrix, switches, sensor ports for Line Sensor Array and MPU-6050, protection circuit for over-current and reverse voltage, and motor drivers.

About the Project

• This development board is used for the Wall-E and MARIO workshops conducted by SRA.
• Designed using KiCAD.

Getting Started with a Development Board

In general, every development board has the following basic features:

• Power Supply Unit

  • Microcontrollers (MCUs) usually run on 3.3V or 5V logic supply voltage while input to a development board is normally 12V for motor and driving/controlling peripheral devices.
  • So, in order to have a single input source, a power section which inter converts this 12V to standard levels like 5V & 3.3V for MCU and sensors is present.This is achieved using a step-down buck regulator.

• Motor Driver

  • Motors usually run on 12V and MCU output is generally 5V/3.3V. So, an external motor driver circuitry is required to control motors according to the MCU input.
  • The SRA board use the TB6612FNG Motor Driver, which is a MOS-based H-Bridge motor driver.

• Sensor Port

  • According to the external sensor types, usually development boards have onboard sensor ports where the sensors can be connected easily. LSA - Line Sensor Array and MPU- Motion Processing Unit have on-board connection ports.
  • Easily available and efficient JST XH connectors.
  • Previous versions used bulky FRC connectors

• Protection against Reverse Voltage

  • The SRA Boards use diodes for reverse voltage protection in the power-line.
  • 12V Motor line and power regulated line have been separated with SS34 and SS54 schottky diodes respectively.

• Protection against Over Current

  • This is done by PTC Resettable Fuses.

• Programmable Switches and LEDs

  • Every development board should have some programmable switches and LEDs for testing, control and debugging purposes.
  • The SRA Board features a 8x8 LED matrix (64 LEDs total) controlled via MAX7219, which provides enhanced debugging capabilities and expressive visual feedback while reducing GPIO usage compared to discrete LEDs.

• Power Switch

  • All versions have a power switch for the motor driver, using which power supply to the motor driver can be toggled. Similarly, there was a switch for the ESP32 MCU.

• Compatiblity of SRA Board with Battery 3- 3.3V 2500mAh Batteries

  • The SRA Board is compatible with 3-cell (3S) Lithium-ion battery packs which use an external BMS (Battery Management System).
  • The BMS helps maintain safe operating voltages and disconnects the battery when the voltage drops below a safe limit.
  • It also ensures balanced charging and discharging of the three cells, improving the overall health and lifetime of the battery pack.

• LD33 (3.3V) to AMS1117:

  • Older editions used the LD33 IC to step down from 5V to 3.3V.
  • This was later replaced with the AMS1117-3.3 LDO, which is more compact and widely used for stable 3.3V regulation.
  • (AMS1117 is also used on the ESP32-DevKitC V4 module.)

• Reverse voltage protection: Diodes to P-MOSFET

  • Diodes placed in series with the power line introduce voltage drop and power loss compared to a P-MOSFET based protection circuit.
  • Due to the higher current requirements of the motors, managing diode size and current rating became difficult.
  • Therefore, earlier versions used a P-MOSFET based reverse polarity protection circuit, which is more efficient and can handle higher currents.

Contributors

• Varun Patil: Designer
• Omkar Nanajkar: Designer

License

• Distributed under the MIT License.