How Anders Engineered a Sunlight-Readable Touchscreen for a High-Power EV Charger

Public EV chargers spend their working lives outdoors, in direct sun, rain, frost and grit, and within reach of anyone passing. For the driver, the touchscreen is the charger. If it can't be read in sunlight, or it mistakes raindrops for touches, the whole charging experience suffers.

This article shows how Anders Electronics worked with a leading EV charger manufacturer to engineer the display, touch and embedded system for its new generation of high-power DC chargers.

At a glance

Customer: a leading EV charger manufacturer, developing a new generation of high-power DC chargers

• The challenge: a touchscreen that stays readable in direct sun, responds reliably in rain, and stands up to heat, cold and vandalism
• The solution: Anders engineered the display, touch, cover glass, optical bonding and a custom embedded board as one assembly
• The end product: 7" 850-nit TFT with double optical bonding, rain-rejecting capacitive touch, 4 mm chemically strengthened anti-reflective cover glass, and a fanless ARM-based embedded board

The challenge

A leading brand within the EVC market approached us as they wanted to develop their charging system to a new generation high-power DC charger in accordance with market drivers and the need to scale as the market volume increases.

Their key demands included the requirement for:

• Optical excellence through best-in-class displays
• To be able to withstand conditions in an outdoor environment, including extremes in temperature, rain, dust and grit
• To be robust and vandal-resistant
• Aesthetically pleasing to meet their brand values
• The user engagement to be a positive experience
• The embedded system to be able to support processing demands of fast charging and driving the User Interface GUI user interface (GUI) and any long-term updates
• Industrial operating temperatures and long-term availability

The solution

We work side by side with our customers to integrate the best solution for their application, giving drivers a fast, reliable interface while the charger handles the power.

We are constantly reviewing our embedded systems to achieve that desired state and were able to provide a customised motherboard based around a low-cost ARM System on Module that takes care of the high-level communications coupled with a microcontroller which manages the charging circuitry.

For the superior viewing experience that was required by our customer in the EVC industry, we suggested a high bright display with Capacitive Touch.

The main environmental concern was reliability of the touchscreen in the rain. By conducting extensive testing, we were able to fine tune the IC firmware to ensure raindrops were rejected as false touches, and human touches (with and without gloves were correctly reported as real user inputs.

The coverlens has customised and optically bonded, a process which dramatically reduces the internal reflections produced between the coverlens, sensor and display layers by filling the air gaps in between those layers with optically clear adhesives.

This not only clearly improves screen readability in brightly lit and outdoor environments, but also greatly improves the mechanical strength of the display. 

Key benefits of optical bonding include:

• Improved readability in sunlight
• Reduced reflections
• Prevents condensation build-up between layers
• Up to 4 times higher contrast ratio
• Improved ruggedness and durability
• Can lower power use, because less backlight brightness is needed

We also provided the display with strengthened glass. This can be achieved using different methods to ensure it can withstand heat, cold and deliberate impact.

Of course, the above solution ticks the box in accordance with performance, however, as a leading OEM, our customer needs and wants to ensure that the product that the person engages with meets their brand values and our extensive delivered just that.

Options available to our customers include:

• Cut outs and custom shapes
  
• Oversized glass
  
• Bevelled edges
  
• 3D Shaped cover glass
  
• Logo, icon printing
  
• Hidden Until Lit (HUL) features
• Spot facing and touch bumps
• Tinted and mirrored glass

These options let manufacturers use these stylised solutions to completely customise their EVC to ensure it not only meets their brand values but stand out from others in what will become a crowded market.

The display, touch sensor, cover glass and embedded computer in a charger often come from different suppliers, which leaves the manufacturer to make them work together. On this project, Anders' display, embedded, firmware and mechanical engineers worked as an extension of the customer's team:

• Touch tuned for real weather: we adjusted the touch firmware through rain testing, so the screen ignores water but responds to human touch.
• A board built around the charger: we designed a custom motherboard with customer-specified connectors and layout for simpler final assembly.
• One complete embedded display stack, not separate parts: optically bonded display with custom coverglass and embedded system were engineered together as a single solution.
• Support beyond the design: we supply the finished assembly through production, with lifecycle planning to keep ensure long-term supply

The end product

• 7” WVGA TFT module with 24-bit RGB interface – 16M colours
• Customised rear bezel to support specially adapted metal mounting plate
• Backlight brightness enhancement – 850nits 
• Industrial operating temperature range: –30 °C to +85 °C

• Customised capacitive touch cover lens
  • Single finger input and gesture support 
  • Supports water rejection
  • Anti-Smudge water repellent coated
  • EMC: Level 3, conducted susceptibility (10Vrms) immunity

• Customised 4mm cover lens
• Chemically strengthened glass with ground edges
• Double Anti-Reflection coated
• Anti-Smudge water repellent coated
• UV resistant black ink printed frame
• Pre-fitted gasket on front glass

• Double optical bonding using optically clear adhesive
• Cover Lens /OCA/Touch Sensor/OCA/TFT module
• UV resistant filter

• Embedded solution
• High performance, fanless embedded system that keeps the interface responsive as software is updated
• Customer specified connectors and mechanical layout for simple final assembly
• Additional application and system required power circuitry onboard
• Industrial operating temperature and a minimum 10-year production lifetime

Want to go deeper? Read our guide to sunlight-readable displays for outdoor use or download the outdoor display design guide