Low cost USB interfaces for AVR microcontrollers

While there are many chips available for interfacing USB to microcontrollers, most of them involve some costs in both development and component count.

Two low cost alternatives to interfacing ATmega microcontrollers to USB are AVR-USB from Objective Development, and the range of USB interface chips from FTDI Chip.

(USB, FTDI, AVR-USB, FT245R, AVR, ATmega, ATtiny)

The firmware method from Objective Development involves little additional component count, as it uses the microcontroller itself for the interface. Any AVR controller with 2k of flash, 128 bytes of ram and the ability to be clocked at 12Mhz can be used. Licenses for the firmware can be open source or by commercial agreement with the company.

As a hardware alternative, the FT245R USB interface chip is available for around AUD $7.00 in small quantities. Unlike its predecessor USB interface chips from the same manufacturer, this chip includes external EEPROM, clock circuit and USB resistors, on the chip itself, reducing the pin and component count considerably (28 SSOP and QFN-32 pacakges). There are FT232 models available which offer a USB to serial UART interface, but the FT245R models are USB to parallel. This allows direct connection to i/o pins of a microcontroller. Advantages of this method include USB 2.0 Full Speed compatibility, royalty free drivers for Windows, OS X and Linux, and complete USB protocol being handled on board the chip. Also, the limited flash memory of the microcontroller is not taken with firmware, as the code required to drive the FT245 or FT232 is minimal.

Tue, 01 Aug 2006 22:03 Posted in ,