Controlling DC Motors from your Linux Box

"Linux is the best general purpose operating system for controlling hardware. It allows fast and well-controlled access to Input/Output ports such as the parallel port and serial port as well as plug in cards. The Linux Gazette has two good articles on how to achieve this, see [1] and [2]. If you need real time response, consider the RTAI extension of Linux, again Linux Gazette has some very useful articles that use RTAI to achieve motor control [3], make a stroboscope [4], and use a joy-stick to control servo motors [5] .

"Many of these approaches rely on direct access to ports such as the parallel port, but this is becoming increasingly difficult as laptops and newer desktops rely on USB as the sole input-output (IO) mechanism. Hardware access via USB requires a plug-in USB module that translates USB to basic digital IO, and if possible analogue IO. These boards are relatively cheap, starting from about US$35. It's also possible to build your own USB interface based on Open Source designs such as VUSB [6] .

"In this article we will show you how to use a very flexible USB interface board called Open-USB-IO [7] to achieve speed control of a DC motor without any form of shaft encoder. Open-USB-IO provides a lot of options for a very reasonable price. Notable hardware interfaces include digital IO with switches and LEDs, analogue inputs, three channels of PWM (Pulse Width Modulation), a serial port, and seven open collector drivers for motors. The USB stack is written in C that runs on an ATMEGA32 microprocessor; remarkably, you can add your own code to the USB code and then use a symbolic debugger to debug that code. Open-USB-IO hardware can thus be controlled from code running on the Linux box as we will do in this article, or from code that runs on the ATMEGA32 microprocessor (if we get enough requests to the editor I will write an article showing how to write and debug code on the microprocessor from the Linux environment). The web site also has an extensive manual with many examples, and the full circuit of the board."

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