Jon Titus Blog

During the last two months, announcements of new touch sensors and touch-sensor capabilities have arrived from Silicon Labs, Freescale, and Atmel. But the technologies differ and give engineers a variety of capabilities to use in their designs. Here's a quick overview of the technologies and links you can follow for more information. On November 6, 2009, I added new information from Cypress Semi. (Note, this blog entry runs a bit longer than usual.)

Atmel -- maXTouch capacitive touchscreen controller

The mXT224, Atmel's first maXTouch touch-sensor controller and microcontroller IC lets developers place as many as 224 sensing nodes across a 10-inch display screen. People can use a stylus, finger, or even a fingernail to draw, sign their name, or write graffiti-like characters via a touch screen. The chip scans its entire 14-by-16-element sensor array every 4 msec, so it can accurately capture even fast data entry from script writing, for example. The chip offers an 80:1 signal-to-noise ratio, which is critical for the chip to accurately detect adjacent or weak signals, and for precise reporting in noisy environments found in products with electrical noise from radio transceivers, LCD drivers, and battery chargers, among others.

The chip's includes an XMEGA microcontroller that helps the the touch-sensor circuits ignore unintentional activity such as a facial touch when a person puts a cell phone up to their ear. The chip can also reject contact made when someone grips the side of a display, perhaps on a tablet PC. The MCU also can unambiguously sense all touch points on an LCD display. For more details, visit: www.atmel.com/dyn/products/product_card_touch.asp?part_id=4620. Atmel has several videos and additional information at: www.bulldogsolutions.net/AtmelCorporation/ATM_LandingPage/index.aspx?bdls=21067. Atmel should have the EVK-MXT224A touchscreen evaluation kit ($US 400) available now. In addition to the maXTouch device mentioned above, Atmel has other touch-sensor hardware and software.

Silicon Labs -- QuickSense Family

When you need touch sensors that act like buttons, dials, wheels, and sliders, the new C8051F800 microcontroller (MCU) family from Silicon Labs will do the job. According to the company, the C8051F800 MCU family includes a 16-bit capacitance-to-digital converter (CDC) that performs a conversion in 40 microseconds. The high resolution of the CDC lets firmware compensate for changes in sizes, shapes, and material properties that can occur between the time you build prototypes and finally go into production. The F800 devices use one I/O pin per control rather than employ a matrix of lines through a panel. (The company's F700 family of MCUs handles the latter type of touch sensors.)

Silicon Labs sells a development kit, C8051F800DK ($US 99.99), that includes everything you need to start a design or evaluate the touch-sensor MCU. Contents comprise an integrated development environment (IDE) for the 8051 CPU, a target MCU board, cables, and power source. The company's free QuickSense Studio software helps simplify the design of touch-sensor-based designs. Its several applications guide developers through a development flow that includes graphical configuration wizards, firmware templates, and performance-monitoring tools. These programs interface with the QuickSense Firmware API, a configurable firmware library that provides MCU support for touch sensors. Engineers can find reference designs, application notes, product information and evaluation-board data at: www.silabs.com/pr/QuickSense.

Silicon Labs also has an interesting infrared proximity sensor within its QuickSense family. The QuickSense Front Panel Demo Board (below) includes one of these sensors that I'll write about in another blog.

Freescale Semiconductor -- Touch Sensor IC and MCU Software

Freescale approaches touch-sensors and -sensing in two ways: first with its MPR121 touch-sensor IC and second with software that turns any 8-bit S08 MCU into a touch-sensor control device. The latter is quite interesting because it lets engineers add touch sensors to existing designs that already use S08 MCUs.

The MPR121 chip provides 12 touch sensors monitored by an internal state machine that can detect a touch within 64 milliseconds. Engineers can set independent "touch" and "release" thresholds for each electrode. Calibration of each electrode takes place continuously. When an MPR121 chip detects a touch at an electrode, it generates an interrupt signal for a host controller and communicates switch-specific information via an I2C channel. The chip should work well in a myriad of applications such as front panels, HVAC controllers, numeric keypads, steering-wheel controls, and so on. (The MPR121 builds on the technology Freescale developed for earlier touch-sensor devices such as the MPR083 and MPR084.) For information, visit: tinyurl.com/yh8ktsd.

To help engineers get a head start, Freescale offers a four-board evaluation kit, KITMPR03xEVK (about $US 99). A baseboard accepts an MPR121 chip on a daughter card and two other boards let engineers try several types of touch-sensor electrode configurations. Sensor Toolbox demo software and evaluation software gives engineers full control of set-up and operation registers within the MPR121 chip.

Freescale also offers engineers a way to adapt any of its 300 8-bit S08 MCUs to touch-sensor applications that might take advantage of a rotary touch control, slider, keypad, or individual touch controls. Engineers can obtain a free license to use the Touch Sensing Software Suite in Freescale MCUs. This suite of add-on software coexists with application code and uses a call-back mechanism to indicate when it completes a task. Of course, you'll need unused I/O pins for the electrodes, and some applications might require use of one of the S08 MCU's timers.

Engineers can use a Touch Sensing Evaluation Board (TSSEVB, Price about $US 79) to learn more about the software and how to integrate it into an S08 MCU-based device. The eval board includes four demonstrations that show the use of rotary and slider controls, a keypad, and multiplexed electrodes. The kit includes sample overlays of the type you could design for a real-world device. Learn more about the software and evaluation kit at tinyurl.com/mbc648.

Freescale has created an application note that described how to design touch-sensing electrodes. See: Document Number: AN3863, "Designing Touch Sensing Electrodes; Electrical Considerations and Recommended Layout Patterns," available at: tinyurl.com/ycwgve6.

What are your thoughts on touch sensors and the ease of using them in a design? --Jon Titus

New information, added November 6, 2009

Cypress Semiconductor made two announcements that relate to touch sensors. First, the company has a new family of CapSense capacitive touch-sensing devices that will appeal to designers of consumer products because they can operate with as little as 1.8V. The CY8C20xx6A devices have as many as 36 general-purpose I/O pins that designers can use to implement multiple CapSense interfaces. Because the new family uses the programmable embedded system-on-chip (PSoC) architecture, devices also can control motors, measure sensor inputs, turn LEDs on or off, and so on. For more information on the CY8C20xx6A CapSense family visit: www.cypress.com/go/capsense.

The Cypress CY3280-20x66 CapSense Development Kit includes a development board with ports for the following plug-in modules:

• CY3280-SLM – Linear Slider Module
• CY3280-SRM – Radial Slider Module
• CY3280-TPM – Trackpad Module
• CY3280-BSM – Simple Button Module
• CY3280-BMM – Button-Matrix Module
• CY3280-BBM – Breadboard Module

Second, Cypress announced an automatic-tuning tool for the CapSense touch-sensing devices. According to the company, development of some capacitive touch-sensor applications require engineers to perform time-consuming calibrations for up to 15 capacitance-sensing parameters. The new SmartSense tool, though, automatically establishes these parameters during design work because it dynamically optimizes the baseline and detection threshold and adjusts for the optimum capacitance range.

When engineers use the PSoC Designer software they can incorporate the SmartSense firmware that eliminates the need to retune a design each time the thickness or material used for the interface overlay changes. The SmartSense CapSense firmware module is available today with PSoC Designer 5.0 Service Pack 6 for use with the CY3280-20X66 CapSense Development Kit. Cypress offers development kits for sale through its Web site at: www.cypress.com/?id=2218.