Light that screen!

Posted on Feb 7, 2014

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

Light that screen!
Click here to download the full size of the above Circuit.

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...

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