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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. |
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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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