Taming the Complexities of Designing Touchscreens for Next-Gen EV Chargers
Public touchscreen-based EV chargers are in high demand. Understand the electronic design challenges of EV charger touchscreens and the solutions available to smooth the way.
Governments around the world are pushing to have an increasing number of electric vehicles (EVs) on the road rather than internal combustion engine (ICE) vehicles. According to the International Energy Agency’s (IEA’s) projection, the global electric car stock will expand to almost 350 million vehicles by 2030. Even the IEA’s preliminary numbers from its Global EV Outlook 2023 report in April showed rapid growth over last year (Figure 1).
For these vehicles to provide the most utility to their owners, they will need a charging infrastructure comparable to today’s gasoline stations. For example, the United States is currently on track to install a network of 1.2 million public chargers by 2030.
Figure 1. Growth in electric car sales continues to accelerate, with 2023 set to be another record year. Image used courtesy of the IEA
EV Charger Touchscreens in Demand
While domestic charger units may require only a minimal user interface, public-access chargers are increasingly integrating a touch enabled human machine interface (HMI). A touchscreen-based HMI facilitates functions like user type selection (subscribed member or guest), charging cable type selection, payment completion, display of charging status, pricing tariff selection, start/stop charging selection and even advertisements.
It’s clear that the modern consumer prefers a ready to go, convenient touch-enabled HMI on the charger instead of signal dependent mobile phone apps, like the displays already accepted in gasoline stations or parking meters.
The outdoor nature of the public charger comes with rugged requirements such as challenging temperature extremes, dust/moisture exposure, harsh weather and vandalism resistance while still being able to provide a smooth touch experience. The choice of a great touch controller can take your charger’s HMI design to the next level.
Benefits of a Touch-Enabled HMI
Many charger manufacturers have decided to differentiate their charging experience by adding touchscreens to their charger portfolios. Touchscreens are convenient and allow the Charge Point Operators to provide a smooth experience to their customers independent of their mobile phone’s battery status or signal strength. These touchscreens then become a safe fallback option for the operators.
Feedback from initial charger rollouts shows that the majority of early EV adopters remain a young demographic. An aesthetically appealing design with a cool appearance significantly influences the selection of the charger. In fact, with increasing futuristic EV car designs, a complementing charger design increasingly becomes a huge selling point to the consumer (Figure 2).
Figure 2. Comparison between old charger designs versus modern charger designs
Now let’s analyze each of the key benefits of a touch-enabled user interface on an EV charger.
Smooth Charging Experience
Despite being around for some time, EV charging is still a new technological experience to most consumers. Unlike gas stations, often the operation of the charger is not straightforward or quick. Present day fast chargers take from 20 minutes to one hour to get to 80% of battery capacity compared to a few minutes with gas pumps. Instructional videos or step-by-step guidance can be used to teach new users how to use the terminal and charge.
Once charging is started, the display can show charging status data such as battery status, time remaining, next available charger, weather info and efficient driving tips for that battery type and car type. A frequently asked questions (FAQs) section for local regulatory requirements can be helpful. In case of charger malfunctioning, a display can be used to troubleshoot the malfunction, provide data to the support team and even force stop the charging to release the cable.
Transparent Pricing and Receipts
Applied charge prices, like gas prices, are displayed to the user to motivate them to use the provider’s network and subscribe to a permanent membership. An initial selection of user type (guest or member) allows the operator to offer different payment tariffs and payment modes to the user. Business users can enter their email address to get the receipts for expense declarations.
Payment Mode Selection
A non-member user should be able to make payment for charging without being forced to subscribe to the mobile phone app of the charger network. This increases the customer base for the charge point operator. Therefore, a payment option can also be allowed to be chosen where credit cards can be accepted by RFID NFC reader and a PIN entered on touch screen.
Such a payment system becomes more important if a mobile phone battery has died, meaning one cannot pay through their app, or due to non-availability of internet. Feedback says users don’t want to download a new app at a new place, register a new online account and add a credit card with verification before they can pay. Especially, when the mobile signal is poor at remote places such as underground parking garages or motorways.
Figure 3. Easy payment through a touch screen
In fact, legislation such as the Alternative Fuel Infrastructure Regulation (AFIR) in the European Union (EU) already makes credit card payment mandatory on EV chargers. This means the HMI systems used on the charger will need to meet Payment Card Industry (PCI) compliance.
The touchscreen display (Figure 3) and its controller therefore come with an even tougher set of requirements, and both need to be high performance components that provide the end user with a comfortable and secure charging and payment experience.
Extra Revenue for Retailers
Ads displayed on the charger touch screen at malls or supermarket parking lots can provide retailers with an extra revenue stream.
Charger makers can address a wider geographic location by offering charging experience in different languages. This allows a wider demographic to seamlessly use the chargers as they travel through different locations like in the European union.
Outdoor HMI System Challenges
Successful operation of an outdoor HMI display over its expected long lifetime dictates that several operational issues must be addressed in the design phase to avoid repeated repairs, failures and field replacements.
While most of these issues specifically address the display design and its physical integration into the housing, the choice of a great touch controller can help them reach their full potential and save future costs. With that in mind, let's look at some Common scenarios that can impact the touchscreen display design.
The charger enclosure assembly requirement is typically IP65 rated for waterproofing and IP68 rated for both water and dust proofing. The touch controller should not detect water drops as false touches and only detect real finger/glove touches.
Sunlight Heat/UV Exposure
The display needs to be sufficiently readable in sunlight with high 2000 to 3000 nits (compared to standard displays having typically 1000 to 1500 nits). Anti-reflection and anti-glare coatings on the glass can be used to improve readability.
An ultraviolet (UV) filter could be additionally used to reduce screen damage such as color shifting and discoloring in certain extreme situations. Including an IR filter can protect the display from infrared radiation and prevents heat build-up. However, the thicker the stack display gets, the harder it gets for a touch controller to detect a good touch.
Very Cold or Very Hot Temperatures
The chargers can be used in any country around the world. Even though heating or cooling elements can be integrated in the display to keep it at a normal temperature range, the touch controller also needs to be automotive/industrial grade to operate over the same temperature range.
Normally used in cold weather, thick gloves could also be used in the rain. The touch controller needs to support complex interactions with additional layers of glove material on the surface. For example, if the screen has a map to show the next available charger, then multi-finger zoom must be supported in presence of moisture, whether or not the user is wearing gloves.
To minimize the risk of vandalism, a 5 mm to 6 mm thick IK10 type (hammer proof) glass or 2 mm to 3 mm plastic PMMA is typically used on the displays. The vandalism test spec may vary based on the EV charger installation location and models, but the touch controller needs to detect the finger(s) through this thick glass including with a glove and even with rain drops on the glass.
An airgap can also be used between the screen and the glass, so that in case of vandalism only the glass unit is replaced instead of the whole display. This increases the thickness further making it even harder for the touch controller to detect the touch.
Payment via Credit Card
A payment method could be built into the charger, as explained above. This could be a credit card reader module with a mechanical keypad. In this case, there is no special requirement for a touch controller. However, if a near-field communication (NFC) touchless card reader is also offered, and the user can set the amount or enter their PIN via the display, then the touch controller needs encryption for PIN transmission as per EU, UK and other regional mandates for PCI certification.
If someone cleans the display with bleach or other chemical liquids, this must not impact the display or the touch performance. A touch controller needs to be able to cope with various conductive liquids and should not detect them as touches.
A Range of Touchscreen Features
Addressing all these design needs, Microchip’s maXTouch series touch controllers (Figure 4) offer a range of features that tackle these tough outdoor requirements and optimize the touch experience of your display design. This family of devices supports the following:
- A wide variety of screen sizes (approximately 2 inches up to 34-inch displays) and aspect ratios
- High levels of conducted noise immunity (Class A IEC 61000-4-6 certified)
- Thick cover glass of up to 10 mm
- Airgap of 0.2 mm or more
- Multi-finger thick gloves of up to 5 mm like winter ski gloves or motorcycle gauntlets
- Moisture immunity against water droplets and running water
- Immunity to 3.5% saltwater and other conductive chemical cleaners
- Encrypted messaging and configuration for hiding PIN
- PCI Security Standards Council compliance readiness for payment terminals
- Interoperability with NFC technology. The frequency hopping feature during an NFC active scan avoids conflicts with touch scan frequency (100 kHz to 500 kHz and harmonics).
- Self-diagnostic reporting to indicated touchscreen failures
Figure 4. maXTouch touch controllers offer features well suited for the needs of EV charger touchscreen designs.
In addition to assisting users’ hardware/software integration and providing design/pre-certification guidelines for EV charging systems, Microchip has touchscreen development guidelines and touchscreen design partners to provide support specifically for the HMI aspects of EV charging stations.
EVs and EV charging systems will rapidly multiply in the coming years. For the successful use of both, the charging systems require an effective and rugged HMI. In addition to handling extreme weather conditions, the HMI should provide capabilities that meet and even exceed expectations. User security is a must.
Solutions like Microchip’s maXTouch touch controllers are designed to address such complex systems and meet the challenges they face. They are part of a one-stop shop approach for EV charging system components for system designers.
All images except Figure 1 used courtesy of Microchip
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