Tutorial: How to calibrate touchscreens on TomTom PNAs
This method is a procedure to adjust screen calibration, no guessing involved. It will take up to two hours to accomplish.
First thing to do is read the first two posts in this thread to get the procedure to determine the current screen calibration of
your TomTom. You will need the current calibration as a starting point. Note that you will be adding a file to your TomTom that
will either be named cal.txt-for navcore versions later than 8.051 or calib.txt-for navcore versions 8.051 and earlier
You cannot calibrate the navcore version 10.xx and later TomTom's.
Credit to mpp for this tutorial.
The steps in a very short form:
- Very important! TomTom calibration always runs from the center of the screen to the outside in all four directions, so if your touchscreen center doesn't exactly match the display screen center you're screwed up and will never achieve correct calibration.
Step 1: Locate the center of your touchscreen and match it up against the center of your displayscreen. Do this by shortening your axis first.
Step 2: Spread the axis back up again to better match the outer buttons.
The steps explained in very detail:
Prenotes:
- After using a lot of trial and error I found out, that my TomTom is always calibrating from the invisible, but locateable touchscreen center to the edges of the screen. This behaviour makes calibration much more predictable, but you first need to align the touchscreen center with the displayscreen center, before you can calibrate the axis. My TomTom is a TomTom ONE with FW higher than 8.051. In my case, I wasn't able to input the keys on the very right side (e.g. "0" and "P", including using the zoom bar while in scroll map mode). So, I had to calibrate the X-axis and this will be explained in the following tutorial.
- Always calibrate one axis at a time. Do not try to calibrate axis X (horizontal) and Y (vertical) at the same time.
- Always distinguish between the touchscreen center and your displayscreen center!
- Use a plastic touchpad pen to get exact results. This is very important: you can't do the calibration with your thumb or your finger. You must have a very fine pointed tool to use on your touchpad. Look for a plastic pen on your PDA or smartphone or borrow one. You might also use a non-active ball-pen, but be careful not to scratch your touchscreen. In any case, use extra caution while using a tool on your touchscreen!
- Use a spreadsheet to document your very steps. In columns, you will need to document MinX, MaxX, MinY, MaxY, "MaxX minus MinX" (the result can be useful later on) and three note columns for alignment of left, middle and right display part. Always note your initial values which you got from the diagnostics screen first. This will help you to notice any improvements or drawbacks.
- I am not sure about running a reset while moving from trial to trial during the calibration process. As my TomTom ONE has no built-in flash memory it runs a quick reset ("the drums, you know") when the SD-Card was removed for changing values in the cal.txt. If your TomTom has a built-in memory you might need to run a quick reset for the new calibration values to become active.
Step 1a: Locate the center of your touchscreen
Where is the center of my displayscreen?
Open the input screen, where you can type in an address (that is usually starting from the main menu and trying to navigate to an address in a city). The inputscreen should show a full row of numbers above the usual keyboard layout (qwerty-layout). The numbers are from left to right: 1 2 3 4 5 6 7 8 9 0. Now, your displayscreen center is exactly on the border between number "5" and number "6". So to speak, right in the middle of the display.
Where is the center of my touchscreen?
This is a bit tricky, so please keep up with me. To find out about your touchscreen center, press and touch your screen on number 1 and move your pen (while still pressing the touchscreen) to the right. You might notice, while going from one number to the other that the touchpad in a specific section appears perfectly calibrated. For example, you move with your pen from number 6 to number 7 and exactly on that border the highlighted number changes from 6 to 7. So, the touchpad is perfectly calibrated in that section. This is, what I call, the "touchpad center".
Definition of the touchpad center: First condition to meet: Moving with your pen from one specific number to an adjacent number will result in corresponding highlighted buttons on the display screen. If you experience for example, that the touchscreen seems to be perfectly calibrated between number 6 and number 7, than that's where your touchscreen center can be found. Of course the initial location of that touchscreen center varies with each display AND factory calibration. Second condition to meet: Moving from the touchscreen center to the display edges on each side of an axis will give you the feeling, that the display becomes more and more decalibrated the closer you get to the edges on an axis of the display. To explain this in detail look at the following graph A. It shows a touchscreen, where the touchscreen center exactly matches the displayscreen center (step 1 of the tutorial has already been fully completed!), but the alignment of the numbers on the left and right side of the center still gets worse, when moving to either edge.
Graph A begins
Numbers touched by pen below (represented by 1st row of numbers)
Code:
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Numbers actually highlighted on display above (represented by 2nd row of numbers)
Graph A ends
So, by pressing the right half of the number 9 button you are actually highlighting the zero button already. This is a horizontal off-calibration towards the edge of the screen. Notice how both screens (display and touch) do match around number 5 und 6, while they are very off towards both edges. If you touch the first half of number 2 button, it will actually highlight number 1 already.
Another example:
Graph B begins
Numbers touched by pen below (represented by 1st row of numbers)
Code:
Please Login or Register to see the links
Numbers actually highlighted on display above (represented by 2nd row of numbers)
Graph B ends
Look at the highlighted numbers of example B. When you press 2 you will most likely highlight number 1, press 3 and number 2 highlights, and so on. Look at the "numbers actually highlighted on display above" line. Do you see and feel, that the amount of decalibration gets smaller and smaller when moving from left to right? In detail: when you press number 2 you will get number 1. However with number 9 and 0 it behaves slightly different. Only if you press the first half of number 0, you will get number 9. But if you manage to hit the second half of that button, you will actually highlight the correct number, that is number 0. While the offset on the left side of the screen was a full "-1", the offset on the right side decreased to a "-0.5". So, if the offset only decreases from left to right (and does not increase again on the right side!), your touchscreen center can be found most likely on the outside of your right screen edge and you may therefore cannot locate it right now.
Even if you can already locate your touchscreen center, please shorten your axis a bit as described in the next section.
Help, I can't locate the touchscreen center or my touchscreen center seems to be way out of my display screen? What can I do?
Make the axis smaller at each end. This will sharpen things up and you will be able to locate the center of your touchscreen. Look at your calibration info on the diagnostics screen. Mine was:
Code:
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Notice that the MinX and MaxX have switched positions for the cal.txt file
Notice that the MinY and MaxY have switched positions for the cal.txt file
(If you don't understand where these numbers come from you need to read the first two posts in this thread)
Now, I shortened the X-Axis on each end by 100. On the right side on the X-Axis I subtracted 100 from 920 resulting in 820, and on the left side I added 100 to 98, resulting in 198.
With "820 198 890 114" I was finally able to locate my touchpad center somewhere around 7-8. Feel free to shortened each side of the axis by another 50 or 100 (or more!) until you can positively pinpoint your touchpad center.
Step 1b: Align the center of your touchscreen with the center of your display screen
In order to align your touchscreen center with your displayscreen you will have to add or subtract a number from both x-axis-values. Start with 20 or 40 and then finetune with 3 or 5. In contrary to the shortening of the axis you will now have to run the exact same calculation on each value. While shortening the axis you ran opposite calculations: add to the MinX value, but substract from the MaxX value.
If the touchscreen center is to your right of your displayscreen center (that is button 6 and above), add 20 to 820 and 198 resulting in 840 and 218.
If the touchscreen center is to your left of your displayscreen center (below 5), subtract 20 from 820 and 198 resulting in 800 and 178.
From my experience, the result of adding and subtracting is just the opposite direction. This is a very important point! You add numbers and your touchscreen center will move left. You subtract numbers and your touchscreen center will move right. But just try for yourself. Fine tune until your center lies exactly between number 5 and number 6.
Test to determine, if your touchscreen center matches exactly your displayscreen center: If you move your pen from number 5 to number 6 back and forth and the highlighted number on the displayscreen follows absolutely exactly your direction, then you have aligned the center of your touchscreen and your display screen correctly and can proceed to step 2. Calculate your center by substracting MinX from MaxX. In my case, this was: 852 minus 227 = 540. This was my touchscreen center.
Step 2: Expand your axis again, until your buttons are pretty much aligned.
You do this by adding 40 or 20 to your MaxX value and subtract 40 or 20 from your MinX value. This will spread the axis equally around your center. If you actually calculate your new center, it should still read the value of the "Test" above, 540 in my case!
Now watch the alignment of the buttons going from 5-6 up to 0 and going down from 5-6 to number 1. For testing purposes, always start between number 5 and number 6 and either move to the right or left side. You may notice, that the highlighted number is slightly ahead of your actual touchpad pen position. This is an indication that you should expand more.
The goal is to achieve an alignment in a way, that if you press the very last part of number 9 it will highlight 0 and if you press the very first part of number 2 it will highlight already number 1. This will ensure, that you can access the edge buttons without a hassle. If you do not observe the very same pattern/offset on each side of the screen, your touchscreen center is still not perfectly aligned with your displayscreen center. This may happen due to expanding the axis. So, if during step 2 you find out that your center is not that perfectly aligned. go back to step 1. Use your current values (not the initial ones) to offset to the left or to the right equally to get both centers matched up again exactly on the border between 5 and 6.
Final note: As each TomTom user focuses and touches a number slightly different, you may need to compensate for that. In detail: Me, when trying to input the number 3 with my right hand, I will actually hit the button a little bit more on the right side. However, someone using his left hand might hit it more on the left side due to his different vision angle. So, after all the calibration work is done you might find it useful to compensate for this behaviour in the very end. That is in detail: if you try to press number 3 but get number 4 nearly half the number of attempts or even more, you should move your touchscreen center very slightly (by 3-5) to the left or right in order to compensate for your vision angle.
Any questions, suggestions? Just ask!
Regards,
mpp
EDIT: version 1.2 - typos corrected and more explanations added
EDIT: version 1.3 - some minor corrections and after using my calibrated TomTom for a week now I can assure you, that it is definitely worth the effort.
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