lcd touch screen calibration in stock

Some of the first Android devices up to Android 4.0 (Ice Cream Sandwich) had a built-in calibration option. Depending on the device and Android version, the location of this setting varies but is generally at Menu > Settings > Language & keyboard > Touch Input > Text Input. UnderFinger touch precision, tap Calibration tool or Reset calibration.

Tap the Mode button (see green rectangle in image below) on the bottom edge of the screen to go to the Setup menu. On a wall-mount touchscreen this is accessible after removing the screen from the wall. Portable wired touchscreens have a door below the display that hinges toward you to reveal the buttons and LEDs. The wireless handheld P-LCD has a plastic door that opens at the top (thinner edge, opposite the power button), after which you tilt the antenna up to access the button.

There are separate instructions below, depending on which hardware model and which firmware version it’s running. The model type is on a sticker found on the back of the touchscreen.

A white screen with a + symbol will show up in the top left corner. Tap it with your finger or stylus, and repeat for the other four that subsequently pop up after each press.

Press {Clear} to clear the drawings you make on the screen, {Recalibrate} to start the process over if it still is not correct, or {Close} to return to your configuration, or the Setup menu.

In Paradigm 3.0.0 we introduced gestures to P-TS7 hardware, which requires a thin band of pixels on the outside edge of the screen to detect those movements. The way of calibrating touchscreens in software versions lower than 3.0.0 has enough variability that the calibration may cause that thin band of pixels to be missing from the screen.

Press {Screen} screen button and then press {Calibrate Touchscreen} in the bottom left of the screen. You’ll see a screen much like the previous instructions, however there is no + symbols to touch.

In Paradigm 4.0.0 we removed the ability to calibrate the P-TS7 touchscreens in the field. The factory sets the calibration during manufacturing, and much like your cell phone or home tablet, never should need to be calibrated again. Instead of a {Calibrate Touchscreen} button in the Setup menu, you"ll see a {Test Touchscreen} button, which goes to a white screen with a {Close} button. This utility is great for verifying that it takes touch properly. Pushing and holding the Mode button will also get you access to the test screen.

There are 2 main types of touchscreen technology. Capacitive touchscreens are probably the most common and are found on almost all phones, tablets and laptops. But resistive touchscreens are usually the ones you’ll find on smaller LCD panels for your electronics projects. They are cheaper to make so keep the cost down for your devices.

In simple terms a resistive touch panel is two sheets of film separated by a non conducting layer, usually a gas or liquid. When you press on the screen you force the two film layers to touch and make an electrical connection. The screen’s electronics are able to sense the position of this touch connection using sensors that measure resistance between opposite edges of the panel. Basically the touch point creates a potential divider circuit in both the horizontal and vertical planes of the panel.

These measurements are then translated into values by a touchscreen driver chip and then made available to the Arduino (or whatever microcontroller you’re using).

The touch panel and LCD screen are two separate devices. Although they are bonded together there is no connection between the two. The value sent when you touch the resistive panel don’t match with the pixel coordinate values on the LCD panel. We need to develop an algorithm that will let us translate touch panel coordinates so they match LCD pixel coordinates. This is a process of calibrating the touchscreen.

As we’ve already seen the touch panel driver chip will return X and Y coordinate values based on the resistance measurements horizontally and vertically on the device. These values will vary proportionally across the width and height of the screen. The zero values for the touch panel won’t match the zero values for pixels on the LCD screen, but there will be a linear relationship between the two coordinate systems.

This means that we can model the relationship between the X coordinates on the touch and LCD panels as a straight line graph. Similarly the Y coordinates can be modelled as a separate straight line graph.

To find the equation of each line we need to take a number of readings so that we can match pixel coordinates with their corresponding touch panel coordinates. The number of readings you need to take depends on how accurately you want to model the connection between the LCD and touch panels. We already looked at the simple horizontal relationships. But this also another manufacturing error that we might want to consider.

Having said that, and especially for small screens, this misalignment error is going to be very small. The calibration process involves the user touching the screen at specified points, and the user error is probably going to be bigger than any misalignment error.

For true touch panel calibration, including the misalignment error, you need to use three point calibration. The mathematics for this are a little bit complicated but again you will be able to find an Arduino package which will have this code pre-written for you.

For this project will be using a simple two point calibration which will let us create the linear relationships between the X and Y coordinates but ignore any misalignment errors.

To calculate the linear equations we need the user to identify two points on the screen. We’ll do this by setting a target in one corner, asking them to touch the target and then reading the touch panel values which can be logged against the known pixel coordinate values of the target. We can then repeat the process in the opposite corner. This gives us two sets of values where we have two sets of X coordinates with pixel values and their matching touch panel values, and two sets of Y coordinate values.

To calculate the gradient, m, we need to divide the X coordinate pixel distance between the two calibration points by the X coordinate touch panel distance.

We only need to run the calibration code when the Arduino is first turned on. We can then store linear equations within our software and use them in a conversion function which will allow us to passing or touchscreen coordinates and get back a matching set of screen pixel coordinates.

We wanted to we could also store linear equation parameters in the EEPROM of the Arduino. When we then turn on the Arduino we can check the EEPROM to see if there are any valid parameters and then load those instead of running the full calibration routine.

Now that we are able to create graphics on the LCD panel, listen for touch events on the touch panel and convert touch coordinates the screen pixel coordinates, we can start to create buttons, sliders and other user interface components for our projects. This opens up a very powerful and user-friendly way of communicating with you Arduino powered devices. The LCD screen gives you an infinite array of options on how your device communicates back to the user and the touch panel can replace a vast array of buttons and dials. It’s really down to your imagination to work out what you can do with it.

When you insert the TF card into the Raspberry Pi, power it up, and wait for a while, the Raspberry Pi will start normally. In this case, the touch may be faulty and needs to be calibrated.

Touch will work normally after restarting the Raspberry Pi. With different resistive screens, the accuracy may not be very good using the default calibration parameters, so you need to follow the guide below.

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:

3. The calibration tool we will use is called ts_calibrate. We will also be using a program to check the results of the calibration called ts_test. In order to use ts_calibrate and ts_test, we must first set proper environmental variables. Enter export TSLIB_TSDEVICE=/dev/input/event0 into the command prompt, then enter export TSLIB_FBDEVICE=/dev/fb1:

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:

This calibration data will be written to a calibration file called /etc/pointercal. To view the contents of this file, enter cat /etc/pointercal at the root command prompt.

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!

If you"ve had your Panasonic Toughbook for a while, you might notice that your mouse curser is slowly becoming less and less accurrate. This is normal, but you can easily correct it. You simply need to recalibrate your touchscreen. Calibration is quite simple.

Please note that when calibrating the touchscreen models you do need to apply a bit more pressure than when you routinely use the machine. This is normal. However, please do not apply too much force or you can physically damage your LCD screen below the touch panel.

@texasEE, this is one of the screen’s i haven’t had a chance to personally calibrate yet. I had a chance to test the 4 and 5 inch, so those have it implemented. For the 7-inch, the values are in the device tree overlay, copied from the 4 and 5 inch displays, just disabled:

The mPaint example shows how to perform the calibration and in that process "matrix" is filled in with that data. The example shows storing to the local file system, but if you have another storage path, you can use that. You can see in the fwrite that it writes the "size" of the matrix, just as a binary blob. If the fopen had a path to an sdcard, or if you used APIs to write (and restore) from eerom, that should work just fine.