Light that screen!

Description: The circuit is quite simple and can be utilized as an introductory hardware modification for the NXT platform. A white LED (D1) is powered through a 150-ohm resistor (R1) using the 4.3V power supply from the NXT. The forward voltage threshold for white LEDs is approximately 3.5V, resulting in a current of about (4.3V - 3.5V) / 150Ω = 5mA through the resistor. This current level is sufficiently low to prevent battery drain, as the LED consumes less than one-tenth of the NXT's idle current. The 4.3V supply is activated immediately upon starting the NXT, eliminating the need for programming.

When selecting an LED, 5mm (T1 3/4) white LEDs with a diffused ("milky") casing and a 60° viewing angle are recommended. Other colors, such as yellow, can also be used, but a bright LED is preferred to minimize power consumption while ensuring adequate illumination. The completed LED cable features the LED inserted into a LEGO connector for mounting on the NXT. Depending on the specific LED model, it may fit directly into a Technic hole; if the fit is too tight, some filing or hole enlargement may be necessary.

To begin, a short segment of NXT cable is prepared as described. Only the two central wires are utilized, while the other wires are left longer to serve as strain relief in the finished assembly. A flexible two-wire cable is chosen to connect to the LED, with a piece of coaxial audio cable often repurposed for this purpose. The wires are cut to varying lengths to prevent accidental short circuits without requiring individual insulation. Only the red (ground) and green (power) wires are used, and the LED is soldered to the opposite end of the cable. The shorter leg of the LED should be connected to ground through the 150-ohm resistor, while the longer leg connects directly to the 4.3V supply. Staggered wire lengths are once again employed to avoid shorts. It is important to remember to slide a piece of heat-shrink tubing onto the wire before soldering the LED.

In earlier attempts to enhance the NXT experience, side lighting was added to the screen within the NXT case. However, this approach had limited success, as LCD screens that can be illuminated in this manner typically require a special glass top. Despite the initial effort, the outcome resulted in a bright but washed-out screen display.

This project serves not only as a practical introduction to basic circuit design and LED integration but also highlights the importance of careful component selection and assembly techniques in ensuring successful electronic modifications.The circuit being very simple, this project can be used as a first NXT hardware hack. A white LED (D1) is powered through a 150 ohm resistor (R1) by the 4. 3V NXT power supply. The threshold of white LEDs is about 3. 5V, so the current in the resistor will be about (4. 3V - 3. 5V) / 150ohm = 5mA. This current is low enough to avoid draining the batteries (the LED consumes less than 1/10th of NXT idle current). The 4. 3V supply is on as soon as the NXT is started, there is no need to program anything. Choosing the LED: 5mm (T1 3/4) white LEDs with diffusing ("milky") case and a 60 ° viewing angle are the best. But of course other colors work too (yellow for example). You must choose a bright LED to minimize power consumption while getting good lighting. Here is the finished LED cable. The LED is inserted in the hole of a LEGO connector to mount it on the NXT. Depending on the LED model you get, it may fit directly a Technic hole or not. If fitting is too tight, you may have to either file down the LED a little to make it fit, or to slightly enlarge the hole.

We start with a short end of NXT cable, obtained as explained here. Only the two central wires are used. All other wires are kept longer, they will perform as strain relief in the finished cable. To extend the NXT cable, choose a flexible 2 wires cable that will be connected to the LED. I scavenged a piece of coaxial audio cablefor that. The wires of the cable are cut at different lengths to avoid accidental shorting without needing individual wire insulating. Only the red (ground) and green (power) wires are needed. The LED is soldered at the other end of the cable. The short leg of the LED should be connected to ground through the 150 ohm resistor, the other leg goes directly to 4.

3V supply. Here again, I used staggered wire lengths to avoid shorts. Warning: don`t forget to insert a piece of heat-shrink tubing on the wire before soldering the LED! Back in the early days of MDP, I tried a more direct approach: add side lighting to the screen inside NXT case. I knew I had little chance of success, LCD screens that can be lighted that way have a special glass on top.

I tried anyway, and indeed it was a failure: the screen was bright but completely washed out.