VOIP Capacitive Touch interface
Project Description
Our customer, a leader in cloud and video conferencing techniques, wanted to create a modern and easy to use capacitive touch interface for their video endpoints. Based on their research, they wanted their interface to contain:
- 2 channel optical encoder
- 3 LEDs to indicate status
- 6 membrane switch buttons
- CC1101 transceiver
- Slot for 2 AA batteries
Based on their requirements, we proposed a PCB type capacitive touch interface that uses our custom FORE LIGHT™ technology.
There are several challenges involved in designing and manufacturing a capacitive touch interface. One of them is responsiveness. Consumers expect an instantaneous reaction when they touch a button.
We make sure this is possible by:
- Ensuring a scan rate of 80 scans per second is possible
- Proposing that the interface communicates with their main controller via a full duplex UART link. This means that the keypad interface will communicate button press and release information as soon as they are available and need not wait for a query from the main controller
Another challenge is the robustness.
The keypad is expected to work in all conditions that it may encounter during operation. Generally, this test is performed by testing labs such as UL. Some of the tests performed on this interface by UL were:
- Subjecting a fully assembled interface to sparks from an 8KV ESD test gun on the glass interface, screws and the stand.
- Subjecting the unit to a sweep from 150kHz to 80MHz of an 80% modulated AM carrier, 1kHz modulation frequency, of sufficient strength to cause a 3V RMS noise signal on the wires.
Our design was subjected to such tests and passed them comfortably!
The biggest challenge in this project was the lighting. Since this is a backlit panel, it was important for the customer to ensure that the various selectively lit regions had uniform brightness. Several factors such as variations in the LED brightness, alignment issues, etc. could cause the various regions to have a different brightness.
A test procedure to check uniformity was developed based around a camera and some image processing software. This test procedure works by taking the average brightness of the keypad module and failing modules which have keys outside a particular limit. Results from this test were then used as inputs to tweak our production processes.