In addition to the stable and reliable capacitive touch engine core hardware, this new series of MCUs also have standard communication interfaces which includes USART, UART, SPI and I2C, suitable for applications in a wide range of smart household appliances and IoT terminal equipment as well.
The sensing technology is mainly sub-divided into the following types, resistive type, inductive type, capacitive type, infrared type, surface acoustic wave type, etc. Presently, the majority of touch keys use a capacitive type sensing methodology. The main challenge lies in achieving stability and compliance with EMC specifications. Due to variations in different IC companies touch key design technology and differences in provided engineering service levels, developers may not be able to establish correct test procedures during their early development stage. It is only after the product design has been completed and already in use by customers over a period of time, that performance problems will arise leading to many after-sales customer complaints. This is especially prevalent with AC power supply problems, environmental humidity, moisture, etc., all of which can create false touch detect situations.
Sources of touch key instability and implementing good test techniques:
Common sources of interference
Common interference sources include voltage fluctuations, temperature/humidity changes, electromagnetic interference (RF antennas, walkie-talkies, etc.), power supply interference (motor startups, fluorescent lamp startups), etc.
Applying good test techniques
The following test methods can be used to create practical environments for the testing of general electronic equipment.
1. Functional test: Here the touch keys are functionally tested while the operating voltage is adjusted from high to low and then from low to high in a repeated test.
2. Wet environment test: Use water vapor to cover the touch panel to be tested with condensation, or place the touch panel close to the air outlet of an air conditioner. Higher humidity levels will result in higher capacitance values.
3. Temperature test: Use an oven or hot air to heat up the touch panel for the heating test and put the touch panel into a refrigerator or freezer for the cooling test.
4. Power supply interference test: Test for EFT burst immunity using the standard IEC61000-4-4, GB/T 17626.4. Test the RF field disturbance immunity using the standard IEC61000-4-6, GB/T 17626.6.
5. Space radiation test: Test the radio frequency electromagnetic field radiation immunity using the standard IEC 61000-4-3, GB/T 17626.3 with a test field strength between 3 - 10V/m.
6. ESD test: Use the standard IEC61000-4-2, GB/T 17626.6.
HOLTEK Semiconductor initiated its development of touch key devices in 2006. With a desire to offer excellence in professional customer technical service, HOLTEK established its subsidiary company, Best Solution Technology Inc., in 2008 to solely focus on touch key solutions. To the present date, they have assisted related customers with the volume production of some 200 million units every year. HOLTEK fully intends to continue to support its customers by providing excellence in professional technical services and complete solutions to assist customers with rapid product development and design through to final mass production and sales of finished products.