Wednesday, July 24, 2024

An add-on Interactive Multi-Touch Panel

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At the first ever TI Educator’s conference at Bangalore, we saw projects from hundreds of eager minds, all supported by TI’s support programs. In this article, we take a look at one of the interesting projects that caught our eye — a touch panel that can be added on to any display to make it touch enabled.

The project team consists of 3 engineers, Vasuki Soni, Rounak Singh Narde and Mordhwaj Patel from the National Institute of Technology, Raipur. The project is titled “An Interactive Multi Touch Panel using Infrared Sensors”. It is basically a touch panel that is used to provide a touch operated interface to either a computer or any computer operated device. On fitting this panel on a computer or laptop, one can convert an ordinary monitor into a touch sensitive monitor. It means one can control mouse cursor position on the screen using this touch panel. So, in essence, you can turn every one of your non-touch operated devices into touch-operated ones.

178_2Growing an Idea
Mr Soni says, “This technology presents an idea that is dedicated to the field of education. In our day to day life, we see that the field of education involves more user interaction for better understanding. In the village areas and in many schools/colleges, the major need is to make the education process more interactive. But due to a severe lack of resources, it has not yet been possible for us to provide a solution which is affordable at the village/grass-root level. We sincerely believe that touch technologies have the scope to show a lot of innovation in the same”.

I probe on about how their idea is different from the other touch interfaces out there. Mr Narde replies, “Our idea is not for the consumer consumption market as in it isn’t a glitzy, full of overt displays of non-essential features aimed for the rich and the gadget loving community but for the villages. You can think of it like a development board, consisting of only the essentials. The product may have a lesser resolution compared to the other exisiting technologies like resistive and capacitive touch, but the project, like I mentioned before is intended for the village education program as the whole touch screen assembly that we have worked on is very cheap and it is useful for the interactive computer interfaces for the student education like for drawing, painting and other simple operations of computer that do not require high resolution for tangible user interface.”

There are different levels to the final touch-interface.

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1. Sensor panel for Touch
The sensor panel comprises the major part of the sensing circuitry. These sensors are connected along a line to form the two opposite sides of a rectangle just like that of a Laptop or a computer screen. These sensors are built in the form of modules which contain 8 IR sensors and an IR LED. These LEDs are not actuated all at a time but one by one.

2. Sensor data acquisition
The touch detection system works on the principle that a finger placed in the touch panel obstructs the path of the IR Rays emitted from the periphery of the panel. Due to this, the receivers change their outputs after the reception of the reflected IR Rays. The IR Sensors are basically actuated by a 38 kHz modulated signal to stand out of the noise. At a time, only a single IR LED is activated using the combination of D flip-flop and tristate buffer which provides accurate clock and synchronized switching of LEDs.

When the touch event takes place on the panel obstructing the path of the IR LED, some sensors do not receive the IR Rays emitted from the LED due to the obstruction. /*So we get a type of image as shown below in Figure 2. */

Mr Patel explains further, “Once the data is retrieved, comes our next concern. We now have 96 sensors and 12 IR LEDs. But for the data retrieval from sensors, we don’t have sufficient I/O pins in the Stellaris ARM Cortex M3 microcontroller. Hence we are using the Shift Registers (SN74165) to increase the I/O pins. The data is then collected by the 8-Bit Parallel-Input Serial-Out Shift Register. The serial data coming from each shift register in each sensor module is padded serially in the bit stream which finally reaches the microcontroller and is received using the Synchronous Serial interface.”

3. USB Based Serial Communication with micro-controller
Now the data is ready for further processing. The data bytes received from each module are now sent to the computer. This is accomplished using a USB Based transfer. Soni adds, “We are using Bulk Transfer scheme because the data, which is in the form of an image, has to been sent over USB, which is a long burst data for which the bulk transfer is basically meant for.”


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