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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.


I am prototyping an in-car computing and entertainment system and am hoping you can recommend a touch screen that fulfills my requirements. Can you help?

Hey Touch Guy,

I am prototyping an in-car computing and entertainment system and am hoping you can recommend a touch screen that fulfills my requirements. I’m looking for:

  1. 7″ screen size
  2. Low or reasonable cost unit
  3. VGA and standard AV input with auto or manual switching
  4. Multi-touch capable
  5. Minimum of 800×600 screen resolution
  6. Open frame or chassis mount
  7. Sunlight readable or transreflective with excellent contrast ratio
  8. Drivers for Linux and Windows platform
  9. Able to operate at high temperatures (up to 60ºC / 140ºF)
  10. Wide viewing angle
  11. Power supply of 10-13.6V power for use on vehicle power


Hey Ammar,

Touch Guy finds that he has two categories of customer….one who will describe their product, close their eyes, and when they open them, Touch International will have delivered the perfect touch system to make the product a success. The other half of customers will give greater specification, including materials and possibly the electronics, and we will design to those standards. (There is actually a third type of customer, less common, who will say, “make me one like that” while pointing to a competitive product).

You fall into the second category. Before we can move onto your touch screen, we need to determine which display to go with (item one). The 7” TFT display absolutely offers the best value, probably because it can be made in fab’s that have been fully amortized. It is also the universal donor, because up until a few months ago, all 7” displays had exactly the same dimensions, resolution, mounting, electronics drive and performance. Since this display is the universal donor, you will save money on the touch screen, as our 7” MulTI-Touch projected capacitive sensor has the standard dimensions.

Since the 7” displays are basically all the same, there are a couple of specs you will have to compromise on; the resolution for the display is 800×480 instead of 800×600 and there are no wide viewing angled LCDs in that size.

Now to the good stuff, the touch screen. If you want Linux for USB, then you’re in luck because all of our multi-touch panels conform to Windows Tablet protocol and there are several drivers available in the public domain. Going TouchGuy_Basicwith the SPI or I2C interface is not quite as easy, but we can help. And all of our projected capacitive panels are multi-touch, so no problem there, either. (And of course projected capacitive is the way to go….)

But wait, there’s more! Since this display will be subjected to extreme heat and sun (yes, 140ºF is HOT!), Touch Guy recommends adding a polarizer, light control film, and a heat mirror to the touch screen with an index-matched direct bond to keep the heat off of the LCD, improving the display’s contrast ratio and optimizing its sunlight readability. You may also want to add a transparent heater to the mix to warm up the LCD if the unit is in frigid environments. Finally, if you want your entertainment unit to be REALLY cool, we can add a proximity (Z-axis) sensor to the touch panel so that you can wave your hand near the display and increase the brightness at night.

If you wanna know more, call me and maybe we can do lunch

Until next time,
Touch Guy

My company is developing a sleek new GPS and we’re looking for the right touch solution. We’ve looked at projected capacitive touch screens, but feel the cost will push our product’s price point up too much. What do you suggest?

Hey Touch Guy,

My company is developing a sleek new GPS and we’re looking for the right touch solution. We’ve looked at projected capacitive touch screens, but feel the cost will push our product’s price point up too much. Our touch screen requirements are:

  1. 4.3″ Screen
  2. High Optics
  3. Scratch Resistant
  4. Anti-Glare Screen
  5. Lower Cost Display

Mark Hood, Red Lake Falles, Minnesota

Dear Mark,

So I hear it is so frigid up there right now that cold fusion once again might be proven. The marketing lady wants a fast answer so she can go home for the holidays, so the answer is, buy projected capacitive!

The biggest reason people think projected capacitive is more expensive than TouchGuy_Basicresistive is that you are buying a different product. Resistive touch panels and projected capacitive touch panels are made of the same materials, but the processing is a little different. Resistive touch panels are usually mounted between a bezel and an LCD, and boom, you’re done. However, Touch Guy finds that nobody wants a projected capacitive panel that way. Instead they want the touch panel to BE the bezel and front of the product; they suddenly want zero borders around the edges, the cover lens should have pretty colors, rounded corners, button holes and be almost unbreakable. Oh, and add a high-tech sunlight readable coating, and, for good measure, throw in an anti-fingerprint finish. Guess what….it costs more!!!

The electronic controllers for projected capacitive panels are more expensive than for resistive touch panels, but competition has dramatically dropped the unit price this year. A controller chip for a resistive panel might be less than $1 (or free, if included in the ASIC).

The bottom line is you can either adhere to your requirements and buy projected capacitive or you can lower your standards and buy resistive, cause there ain’t no way you are going to get good optics and scratch resistance with that one. So wedge a projected capacitive sensor into your GPS bezel, put the control electronics into the ASIC, and you will pay about the same price as resistive, and you’ll get multi-touch, with cool, must-have-features, like flick, expand map and pinch.

So with that, my duties as Touch Guy have been fulfilled for 2010!
(And maybe now I can get the marketing lady off my back…)

Until next year,
Touch Guy