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issue: September 2003 APPLIANCE Magazine

Electronics Report
Touch Microcontroller System


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The Padless Touch Switch (PTS) Microcontroller System from Pressenk Instruments and Tyco Electronics is said to be a versatile and reliable option for engineers of ranges, refrigerators, washing machines, and more.

According to Dr. Miro Senk, president of Pressenk, the Pressenk/Tyco integrated microcontroller system can be used in any appliance that requires human interface, whether it be via keyboard or switch. "When you control any type of equipment you need human-to-machine interface," says Dr. Senk. "The system is using a ground-loop system, which carries current and exhibits 'resistance' as a result of touch. The change in the voltage appears on the input of the microcontroller."

According to Dr. Senk, the system can be divided into two sections - input and receiving. The input section comprises a test pulse generator for producing pulses into the ground (earth) or any conductive mass acting as virtual ground such as ground wiring or a metallic body of a machine.

Receiving takes place when the user touches the dielectric element at the sensing location, and a potential variation occurs in the conductive plate during the test pulse due to a capacitive circuit formed between the ground and the user. "The microcontroller then reads the touch," Dr. Senk explains.

One of the main advantages of the system is its flexibility, he says. The system can be used with membrane, tactile, or momentary switches, as well as in temperatures up to 85ºC (105ºF), moist environments, or under water. Touch or slide control is also available.

Reliability is another key feature, notes Dr. Senk. "Reliability is very high since there are no moving parts of the circuit. Ground loop is clearly identified as an electric circuit," he explains. "For example, most membrane keyboards are defective if one key has collapsed or 'closed.' Using the PTS, the keyboard will be functional even when all keys have collapsed. You just lose tactile feeling."

The PTS system can also reportedly offer appliance makers cost savings since it is designed to complement any type of operation interface (OI) and doesn't require testing or evaluation for a specific application. According to Dr. Senk, other touch controllers on the market that are reading changes in capacitance, electric field, frequency, light (IR), and hall effect have to be modified for the microcontroller. The PTS system, however, is ready for operation without any calibration or tuning of individual keys, he says.

The companies currently offer four different microcontrollers - PTS A-4, A-12, A-24, and A-42, with the model numbers indicating the number of touch keys. The microcontrollers are programmed with proprietary software or with output protocol based on a customer's control logic. The system also comes with a SAT electronic switch, which is used to close/open the ground-loop circuit.

 

Pictured is the closed ground-loop or touch condition of the PTS microcontroller system. When a user touches the key at the sensing location, a potential variation occurs in the conductive pad, and the microcontroller reads the touch. CLICK to see the full-sized graphic.

 

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