A-Star 32U4 Robot Controller LV with Raspberry Pi Bridge

A-Star 32U4 Robot Controller LV with Raspberry Pi Bridge - Pololu 3117

Overview:

The A-Star 32U4 Robot Controller LV with Raspberry Pi Bridge is a programmable module well-suited for robotics applications, designed to work either as an auxiliary controller mounted to a Raspberry Pi or as a standalone control solution for a small robot. This A-Star (abbreviated A*) is based on the ATmega32U4 AVR microcontroller from Microchip (formerly Atmel), which has built-in USB functionality, and it ships with a preloaded Arduino-compatible bootloader. Its complement of peripheral hardware includes dual motor drivers capable of delivering a continuous 1.8 A per channel, along with pushbuttons, LEDs, and an optional buzzer for building a user interface. An efficient switching voltage regulator allows the controller to work over a wide range of input voltages (2.7 V to 11 V).

The robot controller board conforms to the Raspberry Pi HAT specification, allowing it to be used as an add-on for a Raspberry Pi with a 40-pin GPIO header (Model B+ or newer, including Pi 3 Model B+ and Model A+) . On-board level shifters make it easy to set up I²C communication and interface other signals between the two controllers, and the A-Star automatically supplies 5 V power to an attached Raspberry Pi. In this setup, the Raspberry Pi can handle the high-level robot control while relying on the A-Star for low-level tasks like reading analog sensors and controlling timing-sensitive devices (e.g. servos).

Pololu have provided a library that helps establish communication between the A-Star and a Raspberry Pi, as well as a tutorial that demonstrates how to use the library and its included example code to build such a robot.

Features:

• Dimensions: 65 mm × 56 mm (2.6″ × 2.2″)
• Programmable ATmega32U4 MCU with 32 KB flash, 2.5 KB SRAM, 1 KB EEPROM, and native full-speed USB (clocked by precision 16 MHz crystal oscillator)
• Preloaded with Arduino-compatible bootloader (no external programmer required)
• All 26 general-purpose I/O lines from the ATmega32U4 are broken out (including PB0, PD5, and PE2); 7 of these can be used as hardware PWM outputs and 12 of these can be used as analog inputs (some I/O lines are used by on-board hardware)
• Convenient 0.1″-spaced power, ground, and signal connection points
• Dual bidirectional DRV8838 motor drivers (1.8 A per channel)
• Buzzer option for simple sounds and music
• 3 user-controllable LEDs
• 3 user pushbuttons
• Reset button
• Level shifters for interfacing 5 V logic to 3.3 V Raspberry Pi
• Power features:
  • 5 V power can be sourced from USB or from a 2.7 V to 11 V external supply through on-board regulator (with several access points for connecting external power)
  • Switching 5 V regulator enables efficient operation
  • Power switch for external power inputs
  • Reverse-voltage protection on external power inputs
  • Power selection circuit allows for seamless switching between power sources while providing overcurrent protection, and feedback about which power source is selected
  • Provides 5 V power to Raspberry Pi
• 6-pin ISP header for use with an external programmer
• Comprehensive user’s guide

Dimensions:

• Size: 65 x 56 mm
• Weight: 23 g

A-Star 32U4 Robot Controller LV 5 V regulator

A major feature of the A* Robot Controller LV is its power system, which allows it to efficiently operate from a 2.7 V to 11 V external source and provide power to an attached Raspberry Pi. The input voltage is regulated to 5 V by a TPS63061 switching step-up/step-down (buck-boost) converter from Texas Instruments. (We also make a standalone regulator based on this integrated circuit.) The regulator’s flexibility in input voltage is especially well-suited for battery-powered applications in which the battery voltage begins above 5 V and drops below 5 V as the battery discharges. Without the typical restriction on the battery voltage staying above 5 V throughout its life, a wider range of battery types can be considered. For example:

• A 4-cell battery holder, which might have a 6 V output with fresh alkalines or a 4.0 V output with partially discharged NiMH cells, can be used to power this A*.
• A disposable 9 V battery powering the board can be discharged to under 3 V instead of cutting out at 6 V, as with typical linear or step-down regulators.

As shown in the left graph below, the LV’s 5 V switching regulator has an efficiency – defined as (Power out)/(Power in) – of 80% to 90% for most combinations of input voltage and load.
 

The A-Star’s components, including the microcontroller and LEDs, draw 30 mA to 40 mA in typical applications (without the buzzer). The rest of the regulator’s achievable output current, which depends on input voltage as well as ambient conditions, can be used to power other devices; this can include an attached Raspberry Pi (which typically draws a few hundred milliamps). The blue line in the right graph above shows output currents at which the voltage regulator’s over-temperature protection typically kicks in after a few seconds. These currents represent the limit of the regulator’s capability and cannot be sustained for long periods; under typical operating conditions, a safe limit for the maximum continuous regulator output current is 60% to 70% of the values shown in the graph.

Documents:

• Pololu A-Star 32U4 Windows Drivers (version 1.3.0.0) (7k zip)
• Schematic Diagram of the 32U4 A-Star Robot Controller (382k pdf)
• Pinout and Power Distribution Diagram for the 32U4 A-Star Robot Controller (8MB pdf)
• Dimension Drawing of the 32U4 A-Star Robot Controller (2MB pdf)
• 3D Model of the 32U4 A-Star Robot Controller (3.95MB zip)
• Drill Guide for the 32U4 A-Star Robot Controller (9.69k pdf)