Touch screen or touch activated technology has been around for a few decades now, but only recently have prices dropped and the technology been (somewhat) perfected. As an input device touch screens offer a more natural interaction that humans are used to, which offers a great advantage for businesses selling to the general public over traditional keyboards and mouses.
This article will look at how to interface to a 4-wire resistive touch screen and find out the X and Y coordinates of the current point being touched. A minimal number of parts will be used to simplify the system hardware, and to focus more on the theory of how it works.
Simple Touch Screen Interface - [Link]
A friend of mine suggested that I build something for a 74xx TTL discrete logic contest at dangerous prototypes, so I figured why not? If you like this design, make sure to leave a comment on their website for my competition entry.
The Masochist’s video card is a pure TTL discrete logic design that generates the necessary video signals for VGA. The project name came about after the hours I spent wire-wrapping the project together yielded painfully raw fingertips. So be fore-warned if you duplicate this project, don’t abuse the wire-wrap tool!
Masochist’s Video Card - [Link]
The keyboard is the most common way for humans to input information into a computer. It has been around since before computers were main-stream and everyone was still using typewriters. Because of this prevalence in society, it’s important that we understand how to interface to the basic PS/2 keyboard.
This article will describe and show you an example of how to create a system capable of interacting with a keyboard in order to understand what keys have been pressed. The example system will be built on a breadboard using a PIC microcontroller to communicate with the keyboard and display output.
PS/2 Keyboard Interface - [Link]
VT220 serial console (circa 1983) set up as a terminal for Mac Pro (2010) – [via]
My biggest source of information getting this going was Paul Weinstein’s post about setting up an Apple IIc as a terminal for his Mac mini (which is similar, but not quite the same since the IIc still has to emulate the terminal in software). I got the same USB-to-serial adapter, a Keyspan USA-19HS ($27), which has Mac drivers that I can happily confirm work well with 10.7 Lion. I also needed a null modem cable ($7) and 25-pin female/female converter ($4) to connect it to my VT220.
At first I used the same method as Paul to get it working, gluing together the terminal and OS with a utility called screen. As Paul notes, this is less than desirable. It still requires you to open a software terminal to make the connection, and you’re still operating through a layer of emulation. On most Unixes you can simply add a line to /etc/ttys and everything just works via getty, but apparently this has been disabled in OS X since 10.5.
Eventually I found this page, which explains the problem and how to fix it. After adding a line in /etc/gettytab to manually set the terminal type to vt220-8bit everything works perfectly! A real hardware terminal directly connected the old fashioned way, with no emulation. Awesome
VT220 serial console (circa 1983) set up as a terminal for Mac Pro (2010) - [Link]
3in1 universal converter. Based on FTDI 232R chip seen as normal COM port, and two serial converters MAX232 and MAX485. Allow to be used as RS232, RS485, or UAR TTL converter. Connections parameters can be set through the system, as in normal COM port. Supported speeds: 110 to 921600bps.
3in1 converter – USB to RS232, RS485, UART - [Link]
This is a low-cost prototype electrooculography (EOG) system, based on the ATmega328P, that allows people with motor disabilities to write text on a screen using only eye movements. Luis explains: [via]
The human eye is polarized, with the front of the eye being positive and the back of the eye being negative. This is caused by a concentration of negatively charged nerves in the retina on the back of the eye. As the eye moves the negative pole moves relative to the face and this change in the dipole potential can be measured on the skin in micro volts. To translate this voltage into a position, two sets of electrodes are used to measure the differential voltage in the vertical and horizontal direction, on this project, however, just horizontal movements are recorded.
Honduran High Schooler’s Low-Cost Eye-Controlled Interface – [Link]
Matt writes in about RTS/CTS handshaking and waveforms…
I recently had the need to add RTS/CTS handshaking to the serial connection between my PC and my ATMega. I struggled with it for a time due to some misunderstandings on my part, and because I couldn’t find a writeup which described how the handshaking is supposed to work, and (more importantly for me) how it’s supposed to look. I eventually got it to work, and wrote it up in a way that would’ve been useful for me when I was trying to figure out how to make it work.
RTS/CTS handshaking and waveforms – [Link]
This hack is accomplished using the Universal Breakout Board (UBB) which slides into the SD slot providing access to these signals. The UBB interfaces with the VGA connector via a handful of resistors. The schematic and code for the Ben are posted on the project’s site.
Bitbang VGA from an SD card slot – [Link]