USB Ultrasonic Controller Board

(click photo for full-size image)

This board is a redesign of the current ultrasonic control board, designed to control the ultrasonic ranging modules on Brak's base. Brak currently has twelve ultrasonic sensors arranged at 30 degree intervals around the base. Each board controls four sensors, including the firing order/pattern, interval, and time-of-flight calculations.

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

Replace the I²C interface with a USB interface
Shrink the printed circuit board size
Use a newer microcontroller
Control the power to each transducer
Let the microcontroller automatically detect the ranging modules
Add additional diagnostic LEDs

The current boards have functioned adequately. Most of the changes above are slight improvements, such as the ability to only turn on the ranging modules when needed. Tests have this significantly reduces power consumption. A less important improvement was replacing a set of jumpers on the board which needed to be "set" for each ranging module. The new boards can detect which sensors are present (or at least functioning) and can send this information back to the PC.

The current boards do have one major problem, though, which is reliable power on the board. A design flaw (and and unforseen change in microcontrollers) meant that when the board power-ups the sensors would be "on"; this sometimes caused the microcontroller to hang without a means to reset it.

Design details

The design is still in the "design stage". Steve Prudhel (BSCpE 2001) designed a prototype for his senior project in 2001. His work was expanded during Summer 2002 and a printed circuit board was fabricated in October 2002. The news boards use these new components:

A Cypress AN2131S EZ-USB™ 8051 microcontroller with integrated USB serial interface engine. This microcontroller features code in on-chip RAM which is bootstraped from the PC host when the device is plugged in. It also supports input capture which is really useful for accurately determining the time-of-flight of the ultrasonic signal.
A Texas Instruments SN65220 USB transient noise suppressor for circuit protection.

Additionally we're using General Semiconductor/Vishay GF9926 MOSFETs to supply power to each ranging module. Combining these with some 7405 open-collector inverters, one 7403 open-collector 2-input NAND gate, and some program logic, and we don't need the jumpers anymore. When a board is powered on there is a short delay before we can sense anything with it. During this interval, the board (if present) will pull its ECHO signal low. If ECHO doesn't go low, when we know there's no board present.

The main software for the new board has been rewritten in C. It is based on some of the earlier code for the EZ-USB that we started developing in Fall 2000 and was enhanced by Steve and myself. It's still a work-in-progress but seems to work fairly well thus far.

Board designs

The board was designed using CadSoft's Eagle layout editor. It has the advantages of (a) being pretty powerful, (b) allowing PCB layout, (c) being cheap, and (d) supporting Linux. The designs are provided below as CadSoft schematic/board/library files, as well as PostScript and PDF copies of the schematics.