My interactive table consists of 200 LEDs, which illuminate when you place an object on top of the table.

Check out my Youtube video : Table Interactive à 200 LEDs

Instead of using a central microcontroller and using the Multiplexing technique, I decided to control my table with 25 microcontrollers. My table has 50 pixels; Knowing that an Attiny85 controls 2 pixels, I had to use 25. I use an Attiny85, but one could very well use an Attiny45 since the programming code is not very large.

One pixel has 1 phototransistor, 2 Infrared LEDs and 4 white LEDs of 3 mm. Each pixel measures 10 cm by 10 cm. To control the 4 white LEDs, I use NPN transistors that amplify the light and are very fast to ensure the LEDs turn on or off.

The principle of operation is very simple. There are 2 infrared LEDs that send light permanently. When an object approaches, the infrared light is reflected on the object and is captured by the phototransistor. This one analyzes the quantity of infrared light and according to this quantity, the 4 white LEDs will change of intensity.

The phototransistor is equipped with a filter that blocks daylight; So it only picks up the light from the infrared LEDs. The reason for using infrared LEDs comes from the fact that the human eye is not able to perceive their light so the effect produced is even more extraordinary. Both the Infrared LED (VSBL3940) and the phototransistor (TEFD4300F) are available in the Vishay section of Farnell.

To program my Attiny85, I use my Arduino UNO. To learn more about how to program an Attiny85 with an Arduino, click here.

On my table, I installed a window to protect the top of my electronic system, but I realized that it blocks some of the infrared light. I use a completely transparent glass 4-5 mm thick. Care must be taken not to choose a glass that is too thick otherwise the device will not work as well.

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<--- Schematic	<--- Complete schematic
<--- Hexadecimal	<--- Source code in C