How does a Mouse know when you move it ? || How Does a Computer Mouse Work ?
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You've probably used a computer mouse for thousands of hours, and yet, have you ever stopped to wonder how it works? Well, essentially the modern computer mouse is a fusion of 7 different technologies and some rather simple engineering. It would take over an hour to cover all of this. The technologies are intense, so in this video, we're going to focus on just one, the image sensor, and find out what really happens when you move your mouse. Move around on the mouse pad. After that, we'll take a look at a gaming mouse and see how some mice have 25,000 dpi or dots per inch, while others only have a few thousand. Stay around and let's jump right in. Underneath this mouse, we have the Image Acquisition System or IAS, which is made up of an infrared LED, a pair of lenses, and the image pixel array. Infrared light generated by the LED passes through a lens and illuminates the surface directly under the computer mouse. Next, infrared light bounces off the surface, passes through a second lens, then a smaller aperture, and finally hits the sophisticated image pixel array, or image sensor, which measures sixteen hundred . Made of pixels, placed 40 X 40. Important: Your mouse does not capture the color or design of the mouse pad or surface. Rather, because the light is emitted at a shallow angle, it illuminates the textures, or ridges and valleys of the surface, sort of like a sunset while falling over rolling hills. The tops of the hills catch and reflect the light and are illuminated, but the light does not reach the valleys, and thus they remain dark.
Your eyes may only see a similar black mouse pad or wooden table, but due to the shallow angle of the infrared light and the focus of the lens, the image sensor is able to capture topographically and artificially complex landscapes. Note that if the surface was perfectly smooth, without any flaws, the mouse would struggle to operate on it. This is why some computer mice do not work as well on glass. Note: Some mice are better at detecting glass. surface imperfections]. In addition, this image sensor is supported by its 1600 . The pixel only focuses on a small area of 1/200th the size of a penny, immediately below the mouse. The key, however, is that the image sensor takes 17,000 pictures of the surface every single second, and thus, even if you move your mouse on the mousepad for just a tenth of a second, the image sensor will take about 1700 photos during that instant. Take a step And here's the kicker to this technology: Your mouse doesn't save any of these images, rather, every time it takes a picture, it compares it to the previous 59 . does from microseconds ago. The microchip then uses the difference between the two images to determine the change in X and the change in Y, or briefly how far and which direction you moved your mouse over that in seventeen-thousandths of a second, or 59 microseconds. Let's dive a little deeper into this idea. If we have two images of topographic surface textures taken 59 microseconds apart, how exactly does the microchip determine the change in X and the change in Y between them? Well, to calculate this, two images are sent to a part of the microchip called the Digital Signal Processor, or DSP for short, where an algorithm called cross-correlation is executed. As mentioned earlier, each image is composed of 40 by 40 pixels, and each pixel generates a value between 0 and 4095 which is related to the intensity of light that affects that particular pixel. Here we represent values by height. Each pixel's digital signal processor or DSP takes the first image and overlays the second image on top of it. Next, the DSP subtracts all the values of the individual pixels of the second image from the first, and we get a new resulting image. The processor then shifts the second image while leaving the first stationary and continues to calculate the difference between the two images until a position is found where the resulting image is minimized. Amount of change in position a. The resulting image tells us exactly how the mouse moved between two consecutive images taken one seventeen thousandth of a second, providing a value for the change in X and the change in Y, measured in pixels. counts 59 microseconds later another image is captured, and the processor performs the same cross-correlation algorithm but with the new image shifting around, and the previous image constant, resulting in another set of values . The processor continues to capture new images and performs the cross-correlation algorithm 17 times. It then sums up all the values, and we get how far the mouse moved in one millisecond. This combined change in X and change in Y for one millisecond is then sent to the system on a chip which in turn relays Is it e. In addition to your computer information by using
A USB transceiver or Bluetooth [note: point to the bluetooth card]. And this is how your mouse calculates the speed every single millisecond. Let us now have a look at the difference between gaming mice and non-gaming mice. Aside from the sharp looking contours of the mouse, a different number and layout of the buttons, and LED lights, the first major difference is the specified DPI, or dots per inch. Gaming mice have DPI specs of 12,000 to 25,000 while non-gaming mice range from 850 to . are close to 4,000 dpi. But the question arises, what exactly is DPI? Well, when you move your mouse to the right by 1 inch, whatever units your cursor moves across the screen results in the value of dots per inch. A DPI of 2,000 means that your cursor will move 2,000 units for every 1 inch of motion of the mouse. However, how does this relate to the image sensor and the cross-correlation algorithm we talked about earlier? OK, let's say each pixel is this 40 by . The 40-pixel image sensor has a length and height of 30 micrometers with a total square of 1.2 mm by 1.2 mm. If we extrapolate this sensor's pics-els to an inch in length, then we'd need about 850 pixels, which would in effect achieve a DPI of 850. To reach higher DPI, we need to subdivide each full or integer pixel using multiple cuts. Let's take each pixel and subdivide it 4 along the x direction and 4 along the y. Each pixel turns into 25 sub-pixels and now, our 850 dpi sensor has a dpi of 4,250. However, if we were to make 29 cuts along each length of each pixel, we get a DPI closer to 25,500. Note that DPI is a linear unit, while pixels per square inch is a square unit. So now that we have the general idea, how does the particular happen?
Well, a common technique of subdividing the whole pixel into sub-pixels is called interpolation, and the simpler version follows. Here we have 4 absolute or integer pixels, each with the value of the intensity of the light hitting that pixel and, as before, the height of each pixel also representing the value of the surface as an approximation to the texture topography. Next, we draw a line between the vertex two sets of pixels in the X direction, and then draw lines between the two lines in the Y direction. Then, depending on how many sub-pixels we want, we subdivide the lines accordingly. At each intersection, we have a corresponding value for a newly interpolated sub-pixel. Therefore, when you change your DPI setting with the mouse, what you are actually changing is the number of subdivisions in this interpolation algorithm. Here we are showing a bilinear projection. It is called bilinear because we draw straight lines between whole integer pixels. However, a bicubic interpolation, which uses a little more math, can be used to create a smooth topography. An additional difference between gaming rats and non-gaming rats is that gaming rats typically report their movements to the computer 1000 times a second, or once every millisecond, whereas non-gaming rats send data 120 times. It's a moment. Also, the number of pictures taken per second is called the frame rate, 17,000 is only high when you're moving your mouse fast, and it gets smaller when your mouse is still to save battery. Life One important thing to note is that there are a wide variety of rasters out there, and in this video, we've listed the specifications of a frame rate of 17,000, and 25,000 . Resolution of dpi, which are specs for a high end gaming mouse. Specs are typically 4000 frames per . Others range from 17,000 to 1,000 dpi to 25,000, 18 by 18 pixels by 40 by 40, and one reporting rate of 100 to 1000. In addition, we showed a mouse that was a . Uses infrared LEDs for illumination, while some rats use lasers, older rats use red LEDs, and prehistoric rats use a ball. Note that at the beginning of this video we said that there were 7 different technologies inside this com-puter mouse, and so far we've only covered one. The next video we are considering making is on the scroll wheel and how fast we can spin the wheel. If we can get this current video to over 30,000 likes, we'll make sure to make that video. The inside of this mouse is quite a complicated printed circuit board or PCB, and without it, there would be a rather nasty jumble of wires that probably wouldn't even work well. If you want to make your own equipment, you will have to make your own PCB which is rather suitable as this video was made possible by our sponsor PCBWay. PCBWay can quickly manufacture your PCBs at competitive prices and impeccable standards. They also provide PCB assembly services where they populate and solder components to the PCB. Check them out using the link in the description below. We believe the future will require a strong emphasis on engineering education and we thank all our Patreon and YouTube membership sponsors