Resistive or I2C Touch: Which Is Cheaper for an Embedded Design?
September 26, 2014
Both keep cost down, in different places. Resistive touch is a cost-effective touch technology that responds to any object, from a bare finger to a thick glove or a stylus. I²C is an interface choice: a projected capacitive (PCAP) touch screen with an I²C interface costs less than the same screen with USB and draws less power, which also saves cost in the rest of an embedded design. The right answer depends on how the screen will be operated and what the host board offers.
Why is I²C touch cheaper than USB?
Mainly because I²C needs no license fees, so I²C ICs cost significantly less than USB or combined solutions. When we introduced our I²C PCAP touch screens, they were 30 to 40 percent cheaper than comparable USB versions, and the right chip selection could cut cost by another 30 percent without giving up any function.
The savings continue past the touch screen itself:
- I²C touch runs from a supply voltage as low as 1.2 V with extremely low power consumption, so power supplies, handheld batteries, and their peripheral circuits can be very compact.
- Less power means less cooling effort, which saves space, weight, and cost, and the lower heat load extends the life of every component in the system.
- At up to 3.4 Mbit/s, I²C is far faster than an RS232 touch interface.
What does an I²C touch screen need from the host?
Driver support on the host. To speed up design-in, FORTEC Group engineers have prepared I²C implementations for several Linux kernel versions and for Android, and we provide the driver binaries, configuration files, and sample scripts, then adapt them quickly to a customer’s requirements. Our standard PCAP touch screens come with either an I²C interface or a USB HID interface that needs no drivers on Windows, Linux, or Android, with sleek designs and few restrictions on shape, color, and logo for a bespoke version. The range is on our PCAP technology page.
When is resistive touch the better choice?
When the screen may be operated with anything, including thick gloves or a stylus. Resistive touch screens work by pressure: a transparent film is pressed onto a glass or acrylic screen, the conductive layers on each make contact, and the controller calculates the position from the change in voltage.
The analog 5-wire resistive touch screens from Abon Touch, which we supply, show what the technology does well. They are very robust, meet a high industrial standard for touch sensitivity, accuracy, and reliable operation, and are rated from -30 to +70 °C. In most applications the controller communicates with the PC over USB as an HID digitizer and needs no additional driver. Where a driver is needed, it emulates the left and right mouse buttons, and drivers are available for Windows, Linux, QNX, and macOS. A current example is the 10.4-inch AB-1510403181218120801.
Our resistive technology range covers analog 4-wire and the more robust 5-wire touch screens from 5.7 to 24 inches, plus glass/glass resistive touch screens from 7 to 24 inches on a project basis, which allow unlimited glove use and cleaning with all cleaning agents. For a deeper look, see understanding resistive touchscreens.
Can a resistive touch screen be optically bonded?
Yes. With VacuBond® optical bonding, done in-house in Ronkonkoma, New York, we bond resistive touch screens to TFT displays, which makes the display and touch solution more robust and easier to read.
Tell us how the screen will be operated and what it connects to, and we will take it from there. Display, embedded computing, and power expertise sit under one roof at FORTEC, so one engineering team matches the touch interface to the host board and the power design. We source through the FORTEC Group and stay with the project from first samples to series production.
