Tag Archive for: touch controllers

I’m trying to figure out how multi-touch controllers work and have a few questions: Why are certain multi-touch controllers unable to sense more than 2 touches? What are the device limitations? How does a 10-point sensing controller overcome this?

Hi Raji,

So, on this Valentine’s Day you want a date with Multi-Touch? Or are you looking to make that special commitment? Either way, I can help you out …

As Touch Guy says, the best predictor of tomorrow is what happened yesterday. In the long 25 year reign of resistive touch, the electronics went from dedicated touch controllers, to single ASIC’s, and finally to touch controllers as a simple four or five wire connection to the LCD driver chip. For multi-touch, we are in the early stages transitioning from dedicated controllers to ASIC’s. All of the dedicated controllers communicateTouchGuy_Basic with the host via USB. In Touch International’s case, the communication format is Microsoft Windows 7 tablet, which makes the touches look like a whole mess of absolute mice to the host. Using this protocol format, both Win CE 7 and Win 7 will work using the built in driver. Linux also has a number of open source drivers available, and if you follow the common implementations, this will be easy.

Today you can pick your life partner (or at least your touch screen ASICS), as there are about twenty multi-touch projected capacitive ASICS available, with even more coming. Of course, each has its strengths and weaknesses, some of which are cost, signal strength, noise rejection, pen sensitivity, allowable thickness of cover glass, speed, number of detectable touch points, availability, and so on. And, if you are looking to make that life-long commitment, but are worried about compatibility, then rest assured that of the ASIC’s I know, all have both I2C and SPI interfaces; a few have USB built in, but a USB peripheral chip can be added to any of the interfaces.

Now, if you’re looking to make multiple commitments (think HBO’s Big Love), there is no I2C dependency and you can run multiple partners on the same bus. Some of the ASIC’s have the address hard-wired in, and some ASIC’s allow the programming of the address. Regardless, you can talk to multiple suitors at the same time. Be aware, however, that there is no “standard” touch format on the I2C, as there is with our USB implementation, so how you communicate your touches will be up to you in some cases, and up to the partner chip in others.

And Touch Guy is off to bestow the ladies of his life with chocolate covered cherries.


If I switch from a curved touch screen to a flat panel, will there be compatibility issues? Please Help! – Nicholas J. Kriz, Eden Prairie, Minnesota

Dear Mr. Kritz:

It is your lucky day! If you had asked for a single curved 13 inch touch screen, the answer would be iffy, because Touch International made their last resistive touch screen in that size more than ten years ago and we only make a few curved surface capacitive sizes now. But you are changing to a flat panel and you will find that most touch screens are backward compatible with ancient touch controllers (yep, that 13 inch display is ancient).

Here is how to stay in revenue production: First, find out if that round cable is a communication cable, or a touch screen cable. If it is a communication cable (most likely), then you need to unplug and open the monitor (bring beer and always wear eye protection). You can ignore that sticker about dangerous X-rays, but not the one about the high voltage. Once open, find the other end of the cable and get the name and part number for the touch controller so you can figure out what the compatibility requirements are.

You have a few options for how to acquire a new touch screen. You can contact the company that made your old touch screen, tell them the size of the LCD and they will sell you a new sensor which you can integrate in the LCD (using the old controller you removed from the monitor). An easier way is to purchase a touch integrated LCD monitor and you will simply plug in the RS232 (an old, old communication protocol) into the host computer. If the computer is as old as the monitor, there is a chance you will need a CGA (9 pin) to VGA (15 pin) adapter for the video connector. The third option is to use any touch technology you think best, but you will need to access the host computer to replace the touch driver with a universal touch driver from a company called TouchBase.

Have fun, enjoy the beer, and call Touch International if you have any problems.

Until next time,
Touch Guy