Touch sensor creates cost-effective keypads

A new 10-key touch sensor chip can enable reliable and rugged touch controls panel to be produced at lower cost than using mechanical switches.

Quantum Research Group, the charge-transfer (QT) capacitive touch company, has released a 10-key touch sensor chip that will enable reliable and rugged touch controls panel to be produced at lower cost than using mechanical switches.

The QT1100A-ISG is the latest in the QTouch series of charge-transfer sensing devices comprising digital controllers capable of detecting near proximity or touch.

Each key is operated through a channel that projects an independent sense field through over 10mm thickness of glass or plastic.

The channels can be individually tuned for sensitivity via its serial interface.

They can also be user-configured to suit the application.

Cost is minimised because only a few low-cost passive components are needed for each channel.

A control panel using the technology is easily sealed, can be made very rugged and is more reliable in operation than those using traditional capacitive sensors due to a number of patented features within the integrated circuit design.

Reliable operation is ensured through automatic calibration for life, adjacent key suppression (AKS) and burst-mode spread-spectrum modulation.

The QT1100A-ISG recalibrates each channel automatically every time it is powered up, compensating for gradual environmental changes and product ageing.

AKS compares the signal received from each channel to ensure that only the dominant touch registers as a key touch, thereby eliminating false multiple key presses, especially on tightly-packed key panels such as those found on small mobile devices.

Spread-spectrum modulation provides effective noise rejection to eliminate false triggering while also reducing RF emissions.

An external synchronisation pin can be used to suppress mains frequency noise.

The device has SPI and UART serial interfaces along with a scanport output that simulates a membrane keyboard.

It self-detects faults for FMEA compliance, making it suited to applications in domestic appliances, television controls, instrument panels, pointing devices and gaming machines.

The QT1100A-ISG operates from a single 3.3 to 5.0V supply and is housed in a 48-pin SSOP, lead-free (RoHS compliant) package.

An evaluation board for this chip, the E1100, is also available.

Pricing is less than $2 for volume applications.

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