I’m kind of new to the touch screen world and am trying to figure out why it is so difficult to get large (over 22”) multi-touch resistive and projected capacitive touch screens. Also, what are the big advantages and performance differences between the competing multi-touch technologies?

Hi Jim:

So you want to know about big ‘uns?

Projected capacitive, our favorite multi-touch technology, has pretty much topped out at 32 inch diagonal sizes.  There are bigger ones available, but they have those annoying little wires that nobody likes to see.

In the realm of large format multi-touch, we find that infrared, camera (often called optical) and DST are the most commonly used touch technologies for large sizes (+32”), however IR and DST only support two touches. The mainstream projected capacitive and multi-touch resistive technologies are capable of unlimited touches, but are not as easily scalable (note that unlimited touch is controller-dependent, not sensor-dependent). So if you fancy yourself as Tom Cruise on a big 60 inch display, you will probably have to wait for projected capacitive to make it big.

So, what are we waiting for?  We are waiting for transparent low ohm conductors.  You will recall that projected capacitive is an X-Y scanned technology, using ITO for that purpose.  But, white paper fans amongst you will recall that ITO has a relatively high resistance when compared to something like a copper wire.  As the touch sensor gets bigger, the ITO resistance gets higher, and eventually, too high for the electronics to work.  So, what is to be done?

TA DA!  Debuting now, for your viewing pleasure, are nano-wires (think a Chinese population of angels on the head of a pin) and super-fine line copper webs.  Both of these sport the required low resistivity, and only the most critical alien-eye can see them…. we can even coax them into rows and columns.  Expect the electronics to grow as well, but, hey, what is an extra multiplexer or two…

So, Mr. Proctor, looks like your wait is over.  Technology is getting bigger, not smaller, this time.

For even more info on multi-touch, check out Touch International’s Putting the ‘Touch’ in Multi-Touch White Paper and refer to the graph below.

multi-touch-graph

– Touch Guy

Do you have a question for Touch Guy? Send him an e-mail at asktouchguy@touchintl.com.