lf286 Linux USB LCD display with watchdog and buttons

Posted on Feb 6, 2014

This article is the result of the very positive feedback on the hardware articles that I have written so far. You LinuxFocus readers are really a great audience! Some of you wanted to know how to interface the USB bus. So here is a nice solution. We use the LCD display from the May 2002 article and make it work with the USB bus. The whole thing wi

lf286 Linux USB LCD display with watchdog and buttons
Click here to download the full size of the above Circuit.

ll be powered from the USB bus. Therefore you do not need any extra power supply. For this article you need at least a partial installation of the Linux AVR development environment. How to set it up is described in this article: Programming the AVR Microcontroller with GCC. USB is cool because it is a modern interface and it offers the possibility to power the devices directly via the USB bus. The connectors are small and high volumes of data can be transported over a small cable. That`s the positive things about USB. The down side is that hardware design is difficult due the high frequencies and the protocol is rather complex. Just take a look a the specifications (, you want the 1. 1 specification) and you will be shocked. It`s 327 pages long and very difficult to understand. No wonder that there are soooo many faulty implementations of USB devices. A more user friendly introduction can be found at but the specification is still complex. What to do How can we interface our Microcontroller to the USB bus FTDI, a Scottish company, has the solution ( ). They offer a chip which implements a USB serial interface. One side of the FT232BM chip is rs232 and the other USB. In other words you just replace the MAX232 which you previously needed for the power conversion on the rs232 lines with this FT232BM chip and you are done. The FT232BM is a true cross platform solution. Drivers are available for multiple operating systems. The...

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