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Controlling Alphanumeric LCDs With Three Wires

shift

The HD44780 LCD controller is the defacto way of adding a small text display to your next project. If you need a way to display a few variables, a few lines of text, or adding a small user interface to a project, odds are you’ll be using one of these parallel LCDs. These displays require at least six control lines, and if you’re using a small microcontroller or are down to your last pins, you might want to think about controlling an LCD with a shift register.

[Matteo] used the ubiquitous ’595 shift register configured as a serial to parallel converter to drive his LCD. Driving the LCD this way requires only three pins on the Arduino, [Matteo]‘s microcontroller of choice.

For the software, [Matteo] modified the stock Arduino LiquidCrystal library and put it up on his Git. Most of the functions are left untouched, but for this build the LCD can only be used in its four bit mode. That’s not a problem for 99% of the time, but if you need custom characters on your LCD you can always connect another shift register.

If you just can’t spare three pins for a display, you could squeeze this down to just two, or add a second microcontroller for a one-wire-like interface.

Controlling Alphanumeric LCDs With Two Wires

LCD

The Hitachi HD44780 LCD controller is the most common interface to all those alphanumeric LCDs out there, and there are a million and one tutorials for connecting these displays to any microcontroller imaginable. This still doesn’t mean hooking up these displays is necessarily simple, though: you still need at least four wires for the data, at least two for control signals, and power and ground lines for connecting the LCD the traditional way.

Here’s a neat trick for connecting HD44780 displays that only needs two wires. In this setup there’s only a ground and power+data wire. The interesting part of this build is using the power pin to transmit serial data with an RS-232-like format. The only difference is keeping the data line at +5 V when idle; a reasonable-sized cap keeps the display and controller alive when the master microcontroller is transmitting.

This technique does require a bit of logic on the receiving end, which a small 8-pin PIC can handle with ease. Communication between a microcontroller and this “smart” LCD is done at 2400 bps, which even the wimpiest micro can handle. All the software to make this setup work are available here, and we expect an Atmel-based version to hit the Hackaday tip line shortly.

Finding the Fix for a Dimmed 27″ iMac Screen

machack27

Like many with a 27″ iMac, [Gerry's] been experiencing some screen brightness issues. According to him, Apple’s been largely ignoring the problem and the community’s outcry, which led to [Kaos2k] poking around inside to hack together a fix. It’s a solution clearly born from trial and error; [Kaos2k's] initial post on the issue simply recommending “applying pressure” to the panel itself, which would sometimes cause the dim screen to spring back to life.

It turns out that heat (or stress, or something) from the screen causes the solder joints to weaken on the board where a 6-pin connector hooks up, dimming the screen to eye-strain levels. Some Mac users are suing over it, because the problem tends to show up just outside of the warranty window and affects a large number of people. [Kaos2k], however, provided the much needed solution for those looking to get the fix over with: just solder the cable directly to the board. Our tipster, [Gerry], has documented his experiences over at his blog, and was kind enough to make a step-by-step video of the repair, which you can see after the break.

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Case Modder Builds LCD Window; Causes LSD Flashbacks

lcd-casemod

[Chris, aka Mosquito's Mods]  is well-known for some awesome PC case mods. He’s outdone himself this time with an embedded LCD panel as his case window. This use of an LCD is becoming common on arcade games and slot machines. [Chris] was inspired by an arcade game he saw at a local Dave & Buster’s. He started with an off the shelf 16″ USB LCD monitor from AOC. [Chris] then stripped off the back light, diffuser, and reflectors. Left with  the bare panel and polarizers, he then created an LCD sandwich of sorts. First a layer of 2mm acrylic. Then the LCD and panel, along with 4 strips of acrylic forming a frame around the LCD. The frame strips are in blue in the image after the break. [Read more...]

Re-purposing an Old Laptop Display

InitsEnvironment[Tim] found himself with a laptop that had a good 18.4″ screen, but otherwise didn’t run properly. It would be a shame to throw that away, so he decided to salvage the screen by turning it into a standalone monitor. This isn’t exactly new, as he did what many people have done and looked to eBay for an after-market LCD controller board. The real beauty is in the enclosure he built. [Tim] had some scrap wood available from a previous project, so he set about designing a new frame for the monitor, and a very nice adjustable stand, as can be seen in the photo above.

One nice detail is in the control panel buttons. The LCD controller comes with a separate board housing the controls, and while he made a mistake mounting it initially, he ended up with a nice set of oak buttons that match the frame perfectly. He then built a nice backing out of styrene that holds the screen in place as well as housing the electronics.

Overall, it’s a nice looking project, and it is always nice to see electronics re-purposed rather than ending up in a landfill. We can’t help but think this would be a great frame for building a picture frame or a wall-mounted PC as well.

Reverse Engineering an LCD Display

ipod

The current marketplace allows hobbyists to easily find inexpensive, well-documented displays, but what if you wanted to interface with something more complicated, such as the screen on an iPod Nano 6? [Mike] has given us a detailed and insightful video showing his process for reverse engineering a device with little-to-no documentation. Here he covers the initial investigation, where one scours the web in search of any available information. In [Mike's] example, the display uses an MIPI D-PHY interface, which he has never worked with. He learns that the MIPI Alliance will provide design specs in exchange for a signed NDA (Non-Disclosure Agreement) and a modest $8000 fee. Nice.

[Mike] shows off some serious hardware hackery, tackling some extremely difficult soldering in order to set up a proper test platform. He then demonstrates how to use a rather awesome oscilloscope to better understand the display protocol. We found it fascinating to see the video signals displayed as waveforms, especially when he shows how it is possible to count the individual binary values. The amount of information he uncovers with the oscilloscope is nothing short of amazing, proving these little devices are more complex than they seem.

[via Hacked Gadgets]

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Crafting A Liquid Crystal Display

gif Throughout the 1960s, the management at RCA thought LCD displays were too difficult to commercialize and sent their engineers and researchers involved in LCDs off into the hinterlands. After watching [Ben Krasnow]‘s efforts to build a liquid crystal display, we can easily see why the suits thought what they did. It’s an amazing engineering feat.

Before building his own version of an LCD (seen above in action), he goes through the mechanics of how LCDs operate. Light enters the display, goes through a polarizer, and is twisted by a liquid crystal material. The first successful LCDs used two types of liquid crystals – chiral and nematic. By combining these two types of molecules in the right proportion, the display can ‘twist’ the polarized light exactly 90 degrees so it is blocked by the second piece of polarizing film in the display.

Besides getting the right crystals and engineering processes, another major hurdle for the development of LCDs displays is transparent electrically conductive traces. [Ben], along with every other LCD manufacturer, uses a thin layer of indium tin oxide, or ITO. By embedding these clear electrodes in the display, segments can be built up, like the seven segment displays of a calculator or a bunch of tiny dots as found in a TV or computer monitor.

In the end, [Ben] was able to build an extremely simple single-segment LCD display out of a pair of microscope slides. It does modulate light, just barely. With a lot of work it could be made in to a calculator type display but for now it’s an awesome demonstration of how LCDs actually work. [Read more...]