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USB Motor Controller Board

(click photo for full-size image)

This board is a redesign of the current motor control board, designed to control the steering and drive motors on Brak's base. The drive system uses two identical Matsushita GMX-6MP013A 24VDC motors; each requires a minimum current of 200mA and have a rated stall current (when there's so much load the motors won't turn) of 4.5A. The motors also have integrated quadrature encoders which can be used to determine the direction and speed of the motor's shaft.

The main changes and/or improvements designed into this board are

1. Replace the I²C interface with a USB interface
2. Shrink the printed circuit board size
3. Use a newer microcontroller
4. Add dedicated connectors for Hall effect sensors
5. Add a reset switch and diagnostic LEDs

Design details

• A National Semi USBN9603 full speed USB function controller will interface the microcontroller to the USB bus. We've opted to go with an external USB controller since the few 8051-compatible microcontrollers with integrated USB controllers don't seem to have the PWM and input capture capabilities needed for this board.
• A Cygnal C8051F015 8051-compatible 32KB FLASH microcontroller will replace the current Philips Semi 80C552. This microcontroller is easier to obtain (thru DigiKey) than the Philips part and has 32K of FLASH ROM, programmable through a JTAG interface. We're using a Cygnal development board in some of our labs and they have a pretty nice development environment as well, so this choice is driven somewhat by that as well. However, the chip's core also support the SPI (serial peripheral interface) which is used by the USBN9603 (actually, the USBN9603 uses National's MicroWire interface, but it's basically the same as SPI) so that and the ability to alleviate the external ROM and address latch means we should be able to decrease the board size. Its only drawback is the chip is a 3.3V device, and we'll need to add a voltage regulator to accommodate that (this is also true for the new ultrasonic controller board). We're using a STMicroelectronics LF33CDT very low drop voltage regulator.
• A Texas Instruments SN65220 USB transient noise suppressor for circuit protection.

The "analog" portion of the current board has also changed as of Summer 2002. The Allegro Microsystems UDN-2998W dual full-bridge motor driver has worked well but is being phased out of production. It has been replace with an Allegro A3971 dual DMOS full-bridge PWM motor driver. We removed the 4N32 optoisolators but had to add some 74157 multiplexers to augment the control logic. The Panasonic DN8897 Hall-effect magnetic sensor from the previous design has also been kept.

The main software for the new board has required little change except for some slight differences between the two controllers. The biggest change is the use of the USB controller. National provides a developer's kit with example code (unfortunately, none for the 8051 -- kind of a surprise) but with some effort we have been able to get it working.

Partial Parts List

Board designs