why should you calibrate a touch screen monitor made in china

Touch screens are finding their way into a variety of embedded products. Most touch-enabled devices will require a calibration routine. Here"s a good one.

Resistive-type touch screens are normally used in cost-conscious designs. Their construction is simple, their operation is well understood, and the hardware and software required to support them is readily available from multiple manufacturers.

Despite the advantages of resistive-type touch screens, devices equipped with them almost always require that a calibration algorithm be the first task to run when the final product comes out of the box. Calibration is necessary because it is difficult to perfectly align a touch screen"s coordinates to the display (LCD or otherwise) behind it. If a button or other “live” feature on the display is to be properly activated, the coordinates of the area touched on the screen must be sufficiently close to the coordinates of the feature on the display. Otherwise, the software may not correctly act upon the soft button presses.

This article proposes a calibration algorithm for resistive-type touch screens that is both efficient and effective. This algorithm was developed after identifying the sources of touch screen errors and deriving the optimum method for transforming the coordinates provided by the touch screen to match the coordinates of the display. The calibration method requires that three targets or test points-no more, no less-be displayed and touched in sequence to determine the screen"s individual calibration factors. These calibration factors are then used to translate screen coordinates into true display coordinates.

The cross section of a resistive-type touch screen is shown in Figure 1. The construction is simple. Two sheets of glass are brought together to form a sandwich, the interior glass surfaces having been coated with a thin layer of conductive material. Small glass beads maintain a nominal separation between the conductive surfaces. When a finger or stylus presses against the surface of the glass, the material bends just enough to contact the lower sheet. In this construction the spacing between beads determines the sensitivity of the screen. The closer the beads are, the higher the pressure that must be exerted before the top glass sheet will bend enough to make contact.

An equivalent resistive circuit is shown in Figure 2: a touch screen controller (digitizer or A/D) applies the V sources to the ends of one of the conductive layers, while the other conductive layer-on the opposite sheet of glass-plays the role of the potentiometer wiper. The Vtest value read by the digitizer depends on where the glass is touched and the conductive surfaces come into contact. The controller then translates the voltage reading into a binary quantity representing, for example, the X-coordinate of the point where the screen was touched. The voltage potential is then applied to the second surface"s endpoints and the first surface plays the role of the wiper, yielding a value that represents the Y-coordinate.

Controllers may collect 200 or more samples per second. The sampling rate usually depends on background noise and controller quality. A smart controller may also incorporate useful features like the ability to interrupt the CPU when a touch is detected, as well as the ability to sample continuously at a set rate as long as the screen is being touched. The device idles when the screen is not being touched.

Several sources of error affect the X and Y coordinates produced by the touch screen controller. The most important sources of error are electrical noise, mechanical misalignments, and scaling factors. User idiosyncrasies may also play a role if, for example, the finger or instrument used to activate the screen does not maintain continuous contact or pressure against it. Any of these errors can produce unusable data, and all need to be compensated for if the touch screen data is to be useful.

Electrical noise triggered by thermal or electromagnetic effects and system design weaknesses are omnipresent in all kinds of electrical systems. In the case of a touch screen, the A/D conversion is particularly susceptible to electrical noise because of the high input impedance of the A/D front-end circuitry. In addition to carefully laying out the printed circuit board containing the touch screen controller, noise problems are normally addressed by adding low-pass filtering to the A/D inputs. Software also comes to the rescue, usually discarding one or two of the least significant bits of the A/D conversion and implementing algorithms to remove from the sampled stream those data points that fall outside permissible ranges. The same software algorithms may remove errors introduced by the user. Such errors normally manifest themselves as sampled points that fall well outside permissible limits as the applied pressure varies.

Mechanical misalignments and scaling factors are the errors addressed by the calibration algorithm proposed in this article. Consider the images in Figure 3. The circle represents an image shown by the LCD under the touch screen; the ellipse represents an exaggerated set of coordinates that the touch screen could produce if the user were to trace the round image shown by the LCD. The reconstructed image appears rotated, translated, and scaled by a different factor in each direction. The challenge for the calibration algorithm is to translate the set of coordinates reported by the touch screen into a set of coordinates that accurately represent the image on the display.

To derive a general solution to the problem, it is convenient to describe each point as a mathematical quantity. We see from Figure 4 that it is possible to describe each point on the display as a vector PD and its corresponding equivalent, as reported by the touch screen, as a vector P.

It is also reasonable to assume that P and PD are related by a quantity that transforms the display coordinates into the apparent touch screen coordinates, like this:

where M is the appropriate transformation matrix and the object of this exercise. If we can assign values to the elements of the transformation matrix M, then we can solve for all PD points given the P points reported by the touch screen.

Let us proceed under the assumption that each display point can be obtained from a corresponding touch screen point, but that the touch screen point has suffered rotation, scaling, and translation.

If we express the points as (X,Y) pairs based on the vector"s length and angle, both the display and touch screen points in question can be represented by the following equations:

If the reported touch screen points have experienced rotation because of touch screen misalignment, and qr = qD – q is the angular misalignment of the reported point, an intermediate point is expressed by:

Each of the X and Y dimensions is also scaled by its own factor, which we will call KX and KY. Accounting for scaling produces the following equation, which comes closer to describing a display point in terms of screen point coordinates:

We can now make a key, pragmatic assumption in order to represent Equation 5 in a form that will enable us to solve for its unknown quantities. While the touch screen may be rotated with respect to the display, the rotation angle qr should be sufficiently small that we can assume sinqr

The advantage of Equation 7 is that we have expressed actual display coordinates in terms of touch screen coordinates. Restating the above equation we get:

The previous equations seem almost intuitive. Remember, though, that they are only valid when the angular misalignment between the display and the touch screen is small.

Common calibration algorithms use data from two to as many as five sample points to collect calibration information. The exercise above assumes that display point coordinates can be calculated from touch screen coordinates, and that by making simple assumptions we can obtain calibration data by using three sample points-no more, no less. Three sample points are needed because Equations 9a and 9b each contain three unknowns. With three sample points we can obtain sufficient information to set up and solve the simultaneous equations.

Sample points should also be selected based on practical considerations. They must yield non-redundant simultaneous equations, they must not be too close to the edge of the touch screen (where non-linearities are more likely to occur) and they must be widely spaced to minimize scaling errors. The set of points shown in Figure 5 labeled P0, P1, and P2 meet the suggested requirements. Those points are roughly 10% off the edge of the screen, as far apart as the display geometry allows, and yield the following non-redundant equations:

We need to solve for A, B, C, D, E, and F. Once these parameters are known, obtaining display coordinates is as simple as plugging the raw touch screen data back into Equation 9.

The code in sample.c assumes that your device implements a routine to collect calibration data before attempting to use these functions. An outline of the proposed calibration process is shown in Listing 1. After taking those steps, the calibration procedure is complete and your applications can begin receiving accurate position information from the touch screen system. The function getDisplay-Point() is intended to be called within the touch screen controller"s interrupt routine, after the routine has filtered and debounced the data coming out of the digitizer. In a typical implementation, calling getDisplayPoint() would be the last step needed before a point of touch screen data could be placed in the user-input queue.

1. Call setCalibrationMatrix() with a perfect set of values (see sample.c) to set the touch screen driver to provide raw (non-translated) data. This way you do not need to build special functions to access the data. Instead you simply get coordinates from the same mechanism as your program.

Integer 32-bit math is required because the raw numbers provided by most digitizers are 10-bit quantities, and Equations 15 and 18 may yield 31-bit signed values. The equations, as implemented, will work with touch screen digitizer resolutions up to 1,024 pixels, which may be suitable for display resolutions up to about 512 pixels (height or width).

If you want to use these formulas for larger touch screen resolutions, it will be necessary to either use 64-bit integer values or judiciously scale input values or intermediate results to avoid register overflow when calculating the calibration factors.

The function getDisplayPoint() does depend on the calibration matrix containing a set of valid quantities to provide reliable results. The structure of the sample provided uses automatic variables to highlight the relationship between the display coordinates, screen coordinates, and the calibration matrix, but in a practical implementation the calibration matrix may best be a global structure that is properly initialized at boot time.

The touch screen calibration algorithm described here is simple, flexible, and capable of correcting for common mechanical errors. These errors-translation, scaling, and rotation-result from mismatches between the display and the touch screen located above it. They can be compensated for with mechanical means, but the proposed software solution reduces demanding electromechanical manufacturing and quality problems.

If you are experiencing difficulties with the touch screen of the Pathfinder PC such as problems selecting items, the touch screen may require recalibration. This process is simple to perform and will result in increased touch screen accuracy.

The program Touchscreen Utilities is used to calibrate the touch screen on most Pathfinder PCs. To access this program, you must be able to access the PC’s Desktop. This is done by logging into Pathfinder as an Administrator, then logging off. This will return you to the Desktop.

The screen will go white and a red cross will appear on the screen. Simply touch the red “+” sign using a stylus or your finger. It will move to nine calibration points. Once you have selected all nine calibration points, click “Update” to apply the calibration.

I have a machine with Ubuntu 12.04 installed, with dual monitor, via VGA and DVI Interface. The monitor is one touch screen and the other one is regular LCD Monitor.

The touch screen is made in China with some unknown brand, and I am using eGalax Driver. The touch screen is now detected and works, but i need to do some calibration since it does not correctly perform click on touch.

The problem is, when I’m using xinput_calibrator, it shows 4 crosses to be clicked on, because I’m using dual monitor, the crosses is now show 2 on the touch screen (touchable) and the others on the other monitor which is regular non-touch monitor.

i tried to unplug the second monitor and then redo the calibration with xinput_calibration, and then saved it. Restart, all accuracy is fine, and the touch screen is working perfectly. BUT when then the 2nd monitor (Samsung LCD TV, via HDMI) is replugged, the touchscreen calibration was simply like gone, the accuracy is now lost. Touch on a point, the system click on another.

Touch function stops working suddenly when you use the touch monitor or laptop? Have troubles such as touchscreen is unresponsive, touch screen input is offset or writing is intermittent? Let’s troubleshoot these common touch issues and fix them pronto!

When encountering touch problems, please check whether the hardware connection is correct first.(The screen of touchscreen laptop is integrated all-in-one, and the wiring is inside the case. Usually, it is not necessary to check hardware connection problems. You can move forward to next part for software settings.)

External touch monitors usually adopt the USB interface to transmit touch signals. If the USB ports on either side of the computer or touch monitor is faulty, the solder pins are tin stripped, the pin tongue is loose, etc., the touch may be intermittent, unusable, or the screen may not light up at all.

This happens more likely if you plug and unplug the cables frequently. Please re-insert the cables again to ensure the cables are inserted into the right ports and the plugs are not shaky or loose. If the touch screen still does not work, try to buy a new cable from the original manufacturer!

Grease and dust can potentially cause poor electrical sensing on touch surfaces. Use a lens cloth to gently wipe the touch screen and wipe with a little water for the tough stains. Do not spray too much water or detergent.

When touch function stops working, check whether Windows Update and BIOS are updated to the latest version. If it still does not work, follow the following settings step by step to resolve possible problems!

If the USB driver on Windows 10 is not successfully updated, not only the external touch screen cannot be activated, but other USB devices may encounter problems.

Connect the monitor to the computer and go to [Device Manager] → [Human Interface Device]. If the touch monitor connection is successful, the touch screen will appear in the list of Human Interface Devices. Right click the touch screen and follow the steps to update the driver.

Click [Start] → [Control Panel] → [Tablet PC Settings], and then click [Setup] under the display tab. When "Tap this screen with a single finger to identify it as the touchscreen" appears on the screen, just touch the screen.

If the resolution setting does not match the screen, the touch position will also be affected. For example, when you touch certain positions on the screen, it responds on correct points, but clicks on other positions may activate other areas next to them instead.

When the cursor is on the desktop, right click for the setting menu → click [Display settings ] → choose the touch screen (number 2 screen) and select the corresponding resolution(for example, On-Lap M505T resolution is 1920x1080), and then click "Apply".

Click [Start] → [Control Panel] → [Tablet PC Settings], or search for [Calibrate the screen for pen or touch input]. Open [Tablet PC Settings] and select your external monitor from the drop-down menu of Display → Click [Calibrate] → Tap the crosshair each time that it appears on the screen. → click "Yes" to save the calibration data .

Touchscreen laptops and smartphones usually need to be paired with a dedicated stylus. For On-Lap series touch monitors, you can choose a passive stylus with a conductive rubber or plastic disc greater than 6mm diameter. The induction of active styluses differs from brand to brand. If your writing or drawing is intermittent, it is recommended to use a stylus with stronger induction (e.g., Adonit Dash3)

The Mac OS system does not support external touch signals, and the touch monitor can only display images when connected to the computer. This is a limitation of OS compatibility. If you need an external touch monitor for Mac, you can use BootCamp, a multi boot utility that comes with Mac OS. It assists you in installing Windows 10 on Intel-based Mac computers . When you switch your MacBook to Windows 10, you can operate the external touch monitor!

When you connect 15.6-inch On-Lap M505T touch monitor to an Android phone supporting USB Type-C DP Alt, M505T can receive touch, video and audio signals at the same time. However, in case the Android phone OS is not updated to Android 8.0 or latest, you cannot use the touchscreen function on M505T touch monitor.

Note! Not every smartphone with a USB-C connector can be connected to a touch screen. You must inquire your smartphone manufacturer about whether the model supports DisplayPort Alt mode for outputting video signals.

As the projected capacitive touch technology is sensitive to electricity difference, the electromagnetic interference or unstable power current input may cause touch ghost clicks—the screen responds to touches you"re not making. In this case, please eliminate the following interference from your environment :

Sockets in public spaces usually have complicated wiring and power adoption. you may experience current fluctuations occasionally. When the power input to the touch monitor comes from these sockets or extension cords, you may encounter problems of not being able to operate touch screen normally.

Please try to stay away from kitchen appliances in use, such as electric cookers, microwave ovens, etc. Even table lamps may emit a lot of low-frequency electromagnetic waves. These electrical appliances that emit electromagnetic interference during operation may affect the use of your touch screen.

We hope the article has helped you to solve the problems of using touch monitors. If you have any other questions about touch screens, please write to GeChic Customer Service or contact us via FB.

In the previous article, I described the steps needed to install an LCD touchscreen on the Raspberry Pi. In this article, I will show you how to adjust the screen rotation of the LCD to landscape mode, and will show you how to calibrate the touchscreen pointer for optimal accuracy. Just follow the steps below to compete the process of setting up your Raspberry Pi LCD touchscreen:

1. First we need to change the setting for screen rotation in the /boot/cmdline.txt file. This setting is called fbtft_device.rotate=X. By default, this is set to X=0, which results in a portrait mode screen orientation. In order to switch the orientation to landscape mode, change fbtft_device.rotate=0 to fbtft_device.rotate=90. Enter sudo nano /boot/cmdline.txt at the command prompt. There should only be one line in this file. Go to the end of it and you will find the fbtft_device.rotate=X setting. Change the value from 0 to 90:

However, if you try to touch the screen now, you will find that the pointer movement does not correspond to your finger movement. This is because the LCD screen driver and the touchscreen controller driver have separate settings for screen rotation. We need to change the rotation of the touchscreen controller driver to match the rotation of the LCD screen driver.

2. You probably noticed that dragging your finger to the right moves the pointer up, not to the right. This indicates that the x and y axes of the touchscreen are swapped. To correct this, we need to swap the x axis for the y axis. This can be done by changing the swap_xy=X parameter in /etc/modules.

Now if you drag your finger around the screen, you will notice that the y axis (up and down) is correctly aligned with the motion of your finger. However, the x axis (left and right) is still inverted. To fix this, we need to install two more kernel modules, xinput and evtest. xinput is a Linux utility that will allow us to configure input device settings for the touchscreen controller, and evtest is an input device event monitor and query tool.

After the Pi finishes rebooting, you should notice that when you move your finger across the touch screen, the pointer should follow correctly in both axes. If you are using the Raspberry Pi 2 Model B, you will need to complete the calibration steps below before the pointer follows your finger correctly (and make sure that you have enabled startx to load automatically – see step 6 in this article).

You can rotate the screen 90 degrees (as we did in this tutorial) and the power connector will be at the bottom of the screen, but you can also rotate it 270 degrees so that the power connector is at the top of the screen. To do this, simply enter fbtft_device.rotate=270 in the /boot/cmdline.txt file. Then change the DISPLAY=:0 xinput --set-prop "ADS7846 Touchscreen" "Evdev Axis Inversion" 0 1 line in the /etc/X11/xinit/xinitrc file to DISPLAY=:0 xinput --set-prop "ADS7846 Touchscreen" "Evdev Axis Inversion" 1 0. All you need to do is switch the values of the 0 and 1 at the end of this line.

Now that we have our LCD touchscreen up and running, the final step in the installation is the calibration of touch control. This will make the pointer much more accurate and easier to use.

2. Now we need to install the calibration tool we will be using, xinput_calibrator; and other filters for controlling the touchscreen response. Install the tslib library by entering aptitude install libts-bin:

4. Now we can use ts_calibrate. Enter ts_calibrate at the command prompt (make sure you are still in root mode) to run the ts_calibrate program. The program will consecutively display five crosses on different parts of the screen, which you need to touch with as much precision as possible:

Drag the cross around the screen and observe how closely it follows your finger or stylus to test the accuracy of the calibration. Now press the “Draw” button to enter the drawing mode:

This is kind of a long process, but it is well worth it if you want to get the LCD touchscreen set up properly. So if you have any trouble setting this up or have anything to say, please leave a comment below. Also, if you found this article useful, please share it with your friends!

This function is necessary, when the monitors is mounted over head or you use a rear view camera. The settings can be made within the OSD-menu when you have a video source connected and you open the OSD-menu (display is in Video1 or Video2 mode).

A: The 15″ to 22″ touch monitors have a VESA-100 holder on the backside. The 7″ to 12″ touch monitors can be fixed on the wall through the connection track on the backside or through the in delivery included pedestal.

A: The main usage of the touch display is together with a touch PC. That means, that you should connect the display via VGA for the picture and via USB for the touch functionality. Furthermore, all monitors have loudspeakers which you can connect through a 3.5mm stereo jack.

The 7″ to 12.1” touch display series has besides the VGA-connector two video cinch inputs each. To them, you can connect your camera, DVD-player, gaming console or handy with appropriate video/tv-out.

A: If you have problems with the touch, please check if the driver and all cables are installed properly. Otherwise, the most common fault is generated by the protective foil on the touch display. Please take off the protection foil for best use of the display.

A: The touch panel is justified during the manufacturing process. Yet any time, you can make a new justification within the touch software under the “calibration” item.

A: Yes, that is possible. Through the software function “Multi Monitor” you can use more touch monitors at the same time. Also, you can decide, on which monitor the cursor is moved when you touch one of the touch monitors.

A: The touch function is supported through the USB-connector. Just install the enclosed software (drivers for all popular operating systems are available for Windows, Linux, Mac). Please be aware that the software only works with a PC! You cannot control a DVD-player, a camera, etc. by connecting it to the touch monitor with the USB-adapter.

After the successful driver installation, you control the cursor of the PC with your finger or a pen. One touch is the left mouse button, two times fast is a double click and if you press and hold longer it is the klick of the right mouse button. Additional, you can optimize the software settings for your own personal usage.

We"ve all been there. Tapping, swiping or zoom-pinching, there"s often a moment when the touchscreen display on your tablet refuses to respond. How do you overcome this, and achieve tablet-tapping Zen?

As the primary mode of interaction between you and your apps, the tablet touchscreen is vitally important. Any damage inflicted – knocks to the device, scratches or worse – will degrade the touchscreen. Short of paying for a replacement, you will need to make sure the display is kept safe and intact.

The following tips – also suitable for smartphones – will help you resolve your tablet"s touchscreen responsiveness issues. We"ve designed this guide for all touchscreen tablet computers. So, if your Android tablet touchscreen is not working, or your device uses iOS, or Windows, the answers you need are right here.

Perhaps the best place to start in troubleshooting screen responsiveness issues is to make more system RAM available. This may take a moment but should give you an idea of how bad the problem is.

If your Microsoft Surface touchscreen is not working, or you use a different Windows 10 tablet, close as many desktop apps as is practical can before switching to the Start screen. Then:

Restarting a tablet isn"t a case of just tapping the power button to turn the screen off. Instead, the whole device must be switched off and back on again.

After all, how do you fix an unresponsive touchscreen when most of your options are accessible through the screen? The answer is surprisingly simple: connect a mouse.

Knowing which area(s) of the touchscreen are failing to respond correctly can be useful in diagnosing what is wrong. This information would prove useful to any engineer who ends up repairing the tablet.

On Android, free calibration and testing apps are available. Touch Screen Test is a good app that helps you find specific areas where input is not detected.

For devices that are in warranty, this means contacting the manufacturer and arranging a return, or dropping into a store. iPads, for example, can be taken to Apple Stores; Samsung tablets can similarly be taken to Samsung stores. In some cases, doorstep repairs are possible, where the device is repaired in a mobile Samsung-approved workshop parked outside your home. If your Samsung tablet touchscreen is not working, this fast-repair option might be available.

Whether you"re using a Samsung, LG, iPad, or your Lenovo tablet touch screen is not working, check your device manufacturer"s support pages to find the correct steps to arrange repair. Make it clear what steps you have attempted to resolve the touchscreen issues.

As noted above, if your tablet screen is cracked, it can impact touch reliability. Whether big or small, a cracked tablet screen will always fail eventually. Having your tablet looked at by an engineer under warranty is the smart option but isn"t always possible. If your tablet is out of warranty and the screen is cracked, you have two options:

Wondering how to repair a tablet touch screen yourself? For cheaper tablet models repair makes more sense than with premium brands. So, if you have a Vankyo, Onn, Yosatoo, Contixo, or Amazon Fire tablet with a screen that is not working or responding to touch, consider replacing the display yourself. Our guide to replacing a cracked Amazon Fire tablet display will help here.

Most problems can be avoided with care, a screen protector, and a case for your tablet. But where possible, avoid water and don"t get your tablet wet.

Yes, Hope Industrial touch screens use resistive technology, which is pressure-sensitive and can be used with any type of stylus, as long as it is not sharp or rough (which could damage the touch screen surface). Please contact our sales department for more information.

After initial setup, the touch screen should not require periodic re-calibration. Installing new drivers could erase a previous calibration and at time re-calibration is done by preference since some users prefer a different calibration style (e.g.: pointer centered on the finger-tip vs. centered on the finger).

Yes. Our touch screen drivers allow multiple displays to be connected to a single PC whether in mirroring mode (multiple screens showing the same desktop) or extended desktop (a single desktop stretched across multiple displays).

Our Windows drivers allow each touch screen to be calibrated independently whether you are using USB or Serial for connection to the PC. Once configured, the cursor will follow your finger to any connected touch screen. For configuration help or more information, please contact our support group for assistance.

Support for Linux-based operating systems is available through both native drivers, and by using driver-less methods that rely on the HID device compatibility of our touch screens. A full review of the available methods is available on our blog.

A friend of mine got me a EloTouchSystems 2216 AccuTouch USB TouchMoitor, if was apart of a POS system they were replacing, and I am trying to calibrate it on Linux Mint. I have downloaded the xinput_calibrater app and ran it. Here the output from the program:

Additional Information: After posting the question, I realized I did not mention what the touch screen was doing. When I touch the screen and move my finger up and down on the screen, the cursor moves in the opposite direction.