Add a cheap screen

LCD screens are everywhere, in our watches, phones, living rooms, laptops... you get the idea. But, for this month’s ‘Can I Hack It?’ we look at an LCD screen kit that offers us the chance to make our own multimedia player, second screen for a laptop, or even use as part of a miniature arcade cabinet. So, let’s take a look!

General Construction

The HDMI screen measures 165 × 100 × 5 mm thick, and it is fragile, so be careful! There are no mounting holes, so careful consideration is needed to mount the screen securely and safely. A laser-cut frame would be great, and not too difficult to make. The screen connects to the main control board via a flat flex cable. The main control board also connects to a breakout board with screen controls.

Power

The unit is powered by a 12 V 1–2 A supply (not included), and the DC barrel jack should be centre positive, outer GND. Power can also be provided by a breakout connector just above the DC barrel jack connector. This gives us a rough power consumption of 12–24 W, especially when using the included speakers. In the box there is a USB to DC barrel jack lead, and this got us thinking, ‘Could we power the screen from 5 V?’ We tested the USB to barrel jack lead using a 5 V 2.5 A supply, via a UNI-T USB tester and saw that, without the speakers in use, the screen needed 5 V at 0.6 A (3 W), and when using the speakers at half the maximum volume, we used 5 V at 0.8 A (4 W). However, when the screen and audio are used together with a 5 V supply, the screen flickers to the beat of the music. So, if employing it as a screen for an arcade cabinet, we’d advise you to use a dedicated 12 V supply!

Electronics

The HDMI screen has a resolution of 1024 × 600 pixels, and connects to the main control board via a flat flex cable to the TTL port. The latter is rather fragile and uses a plastic locking retainer to hold the cable in place. There is also an LVDS connector for use with screens such as those found in laptops, but compatibility is not guaranteed. Once the screen is connected to the main control board, we have a fragile and short connection. The natural place to store the control board is on the back of the screen, but on the reverse of the board we have many exposed contacts in the circuit, especially the power input. For best and safe results, affix the control board to the screen using self-adhesive plastic standoffs, commonly used in computer cases. If not, then use non-conductive double-sided tape; just make sure there is clearance between the board and the back of the screen.

Everything

The breakout board has controls for the power, volume, and on-screen display menu. All of these are push-buttons that can be desoldered and replaced with larger arcade-style buttons or other inputs. All buttons are connected to a single ground pin on the breakout board, so the GPIO pins they’re connected to are pulled high and, when pressed, go low. This means we can easily hack the inputs with an Arduino or another 5 V-compatible microcontroller, so gesture controls and adapting the inputs for those with disabilities is easy.

Audio is handled via two speakers attached to the main control board via a four-pin JST connector. This is connected to an APA2068 stereo 2.6 W amplifier, enabling decent audio playback if used with an HDMI source. Looking at the pinout of the APA2068, we can see pins 9 and 11 used for the left speaker, and 14 and 16 used for the right, so we could bypass the connector if needed.

Connections

The main control board has lots of connections. An HDMI port supports audio input. VGA and composite ports offer a degree of flexibility for most users. There are also connectors for backlight and composite in, which can be used to breakout the connections and possibly provide an audio input for those using VGA.

Can I connect it to a Raspberry Pi?

The short answer is yes, but you‘ll need to edit your boot/config.txt file so that it detects and sets the correct resolution. Details are supplied in the box.

Screen Connected

Conclusion

This is a fragile, yet capable screen. Sure, the colour reproduction is a little cold, but we can change that in the menu. Sound is acceptable for general use, but for £47 we have a screen and audio that’ll connect directly to our Pi / laptop / DVD/Blu-ray player with minimal hassle. The ability to power from 5 V is handy for portable solutions (you may need a second screen when travelling for work) but this will mean no audio via this board.

The best use case for this screen is for a miniature arcade cabinet (using 12 V supply), as it means that we can use a Raspberry Pi or other computer with HDMI output without the need for a separate audio board. This is a fun board and it is ripe for hacking your next multimedia project!

Screen choice

There is obviously more than one type of screen. In this case, we had a screen with its own control board offering VGA/HDMI and composite inputs. But for around the same money, we can pick up screens from Adafruit. For example, Adafruit has a 5-inch 800 × 480 HDMI touchscreen suitable for use with the Raspberry Pi. It may not be the biggest screen, but for simple retro gaming and media consumption it works well. The caveat is that there is no audio support for the HDMI, so we need to use an external audio amplifier – or if using a Pi, route the audio to the 3.5 mm jack.

Units such as the one we looked at can also be found in various sizes and configurations. A quick glance of AliExpress shows a $9.99 10.1-inch version running at 1280 × 800 resolution via a RealTek RTD2660H HDMI driver chip (as used by Adafruit boards). The downside of this larger screen and resolution is that any LCD panel using the TTL connection will notice a loss of quality, so dropping the resolution to 1024 × 600 would be advisable for media applications.

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