POS machines can be categorized into handheld, desktop, and mobile phone-based systems. Among these, the handheld POS machine—also known as a mobile point of sale—is a portable smart card terminal that performs real-time data processing without requiring a constant internet connection. It uses wireless communication technology and is widely applied in fields such as data collection, mobile billing, identity verification, retail sales, attendance tracking, access control, and inspections. Due to the critical nature of data transmission, POS machines must maintain high reliability. They typically need to pass IEC standards for contact discharge (8kV) and air discharge (15kV) electrostatic tests, making interface protection a crucial design consideration.
Common interfaces found on POS machines include RS232, RJ11, RJ45, USB, and power inputs. Each of these interfaces requires robust circuit protection to ensure safe and stable operation. Below are some common protection schemes for these interfaces:
The RJ11 telephone interface allows the POS machine to communicate with the settlement system via a landline. Since the ringing signal on this interface can reach up to 150V, the overvoltage protection component must have an operating voltage higher than this peak. Figure 1 illustrates a surge protection solution designed by SPSEMI Instant Lightning Electronics for the RJ11 interface. This design includes both differential and common mode protection, meeting the ITU-T K2.1 standard at an 8kV surge level.
SPSEMI Instant Lightning Electronics offers one of the most advanced ESD and surge protection solutions for data lines in the industry. Their SET series features low capacitance, fast response times, low residual voltage, and high withstand voltage, ensuring the reliability of POS devices under harsh conditions.
For the USB interface, which is commonly used in handheld POS machines via a mini-5pin connector, static electricity from external sources can cause data transfer issues or damage the internal chip. A typical protection scheme for the USB interface using SPSEMI’s technology is shown in the following figure.
The keyboard of a POS machine is also vulnerable to static interference. Static charges can enter through gaps in the keyboard and affect the device’s performance. To prevent this, structural improvements such as reducing gaps and increasing the thickness of the silicone pad can help. Additionally, adding a transient suppression diode (ESD) to the keyboard circuit is a common and effective method of protection.
The resistive touch screen on a POS machine is another area prone to electrostatic damage. Human body static discharge can exceed 15kV, and the four corners of the screen are particularly susceptible. The following diagram shows a standard protection approach for touch screen interfaces.
In addition to these components, the power charging port of a handheld POS machine also requires proper protection. Hot plugging can generate transient surge currents that may damage the power chip. Using PTC and TVS components for overvoltage and overcurrent protection is an effective way to safeguard the power supply.
For other interfaces like RJ45, RS232, micro SD, VGA, and display data lines, SPSEMI Instant Lightning Electronics provides comprehensive protection solutions tailored to the specific needs of POS machines. These measures ensure the overall reliability and durability of the device in various environments.
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Shenzhen Sichuangge Magneto-electric Co. , Ltd , https://www.scginductor.com