Plastic touch-sensitive front panels
Thanks to its design and technology, capacitive front panel technology used in next generation electronic products, is gradually deployed in other business areas, thereby offering practicality and a high-tech image.
Fields of application
- Access security and control
- Instrumentation and medical sector
- Automatic vending machines
- Machine tools
- Food industry equipment
Power supply and switching
The front panel is connected to a steady 5-16 V DC power supply source and uses about 5 mA.
As regards the front panel/electronics dialogue, we recommend using the native communication resources of the on-board front panel's electronics.
The electronic module uses standard communication buses from the industrial electronics sector: I2C or SPI.
With capacitive front panels, contrary to mechanical front panels, users do not have the physical feeling of pressing a key.
Therefore, a beeper emits a short sound when a key is pressed to confirm the action.
In addition, each key must be configured according to a number of criteria (response time, detection distance, etc.). The front panel's environment is also an important factor (operating temperature, humidity, etc.)
For all the reasons above, a prototype is developed for every new project, enabling all initial settings to be approved.
Capacitive front panels include:
An overlay made up of a non conductive material
A decorative front panel made in a non conductive material (polycarbonate, polyester, PMMA, etc.) at the back of which is the graphic design displayed to users. The overlay can be made by screen printing or digital printing.
This printing process at the back provides the overlay with high-resistance to chemical or mechanical stresses.
For the overlays of touch-sensitive front panels, we recommend using 3 mm-thick anti-reflective and scratch-resistant polycarbonate, depending on the application.
A touch-sensitive circuit board with electrodes
A touch-sensitive circuit board with the electrodes that make up the keys. This touch-sensitive layer can be made up of:
• a polyester foil screen printed with conductive ink,
• or a printed circuit board.
In most cases, the single-piece assembly with the overlay and touch-sensitive circuit board must be mechanically supported by a backplate.
Where necessary, the backplate must not be electrically conductive so as not to interfere with the front panel operation.
LEDs can be integrated optionally
Backlighting or function SMC LED lights can be added to the capacitive front panels.
Testing and checking
All our front panels are checked and tested. Test reports are available upon request.
Operating conditions and technical specifications
- Service life: up to 50 million operations
- Storage temperature: -40°C, +80°C
- Operating temperature: -40°C, +80°C
- Our front panels are compatible with IP65-compliant equipment.
Benefits of capacitive front panels
Capacitive front panels offer many advantages: ruggedness and service life are their main material assets.
- Contrary to resistive touch pads, which detect mechanical stress, capacitive front panels make it possible to work behind a block of tempered glass. Capacitive front panels are therefore tamper-proof.
- The electronic sensing principle of capacitive front panels also increases an estimated service life to several million operations, against 1 million to 1.5 million for dome switches.
Solutions to overcome constraints
The acknowledgement of the limits of capacitive front panels makes it possible to overcome these constraints easily.
- Capacitive touch-sensitive front panels operate via an electronic sensor, so lamination on a metal surface is not permitted. The touch-sensitive circuit board in the capacitive front panel should be separated from any metal surface by at least 5 millimetres (e.g. multimedia terminals or consumer media). To overcome this, the mechanical design of capacitive touch-sensitive front panels must integrate spacers or isolating seals, and even the creation of an opening to guarantee suitable sealing around the overlay of the capacitive touch-sensitive front panel.
- Although they are not damaged by water projections, capacitive touch-sensitive front panels can however produce abnormal values when placed horizontally: with capacitive touch-sensitive front panels, water has the same conductive properties as the finger. This can be overcome, on the one hand, by tilting the capacitive touch-sensitive front panel when it is known that it will be subject to water projections (e.g. for a boat dashboard). On the other hand, the ability to recognise transient projections will be integrated into the algorithm of the capacitive touch-sensitive front panel and tested during qualification: for example, the software will be configured so that the capacitive touch-sensitive front panel will only acknowledge contacts that last more than one second.
For additional information, please contact us.