POS machines are available in different forms, including handheld, desktop, and mobile phone-based models. A handheld POS machine, also known as a mobile point of sale (MPOS), is a portable device that can process data in real time without requiring a constant internet connection. It typically uses wireless communication to interact with other systems. These devices are widely used in various applications such as data collection, mobile billing, identity verification, sales, attendance tracking, access control, and inspections. Due to the critical nature of data transmission, POS machines must be built with high reliability. They often undergo rigorous testing, such as IEC standards for contact discharge (8kV) and air discharge (15kV) electrostatic tests. This makes circuit protection for the interfaces an essential part of the design. Common interfaces found on POS machines include RS232, RJ11, RJ45, USB, and power input ports. Each of these interfaces requires proper protection to ensure safe and reliable operation.
The RJ11 telephone interface allows the POS machine to communicate with the central system via a telephone line. However, this interface is exposed to high voltage ringing signals—up to 150V. To prevent damage, the overvoltage protection components must have a breakdown voltage higher than this level. SPSEMI Instant Lightning Electronics offers a surge protection solution specifically designed for the RJ11 interface. The circuit includes both differential and common mode protection, meeting the ITU-T K2.1 standard at 8kV. This ensures the device remains functional even under harsh electrical conditions.
For the USB interface, which is commonly used in handheld POS machines to transfer data, static electricity can cause data corruption or damage the internal chip. A typical protection scheme from SPSEMI Instant Lightning Electronics helps safeguard the USB port against ESD events, ensuring stable performance.
The keyboard of a POS machine is also vulnerable to electrostatic discharge (ESD). Static charges can enter through gaps in the keyboard and affect the internal circuitry. One effective way to protect it is by using transient suppression diodes (ESD diodes) to absorb unwanted voltage spikes. Structural improvements, such as reducing gaps and increasing the thickness of the silicone pad, can further enhance protection.
Resistive touchscreens on POS machines are another area of concern. Human body static discharge can reach up to 15kV, and the corners of the touchscreen are especially susceptible to damage. A common protection method involves placing ESD protection components at the four corners of the screen to minimize the risk of failure.
Power charging ports also require robust protection. Hot plugging can generate transient surges that may damage the power management chip. Using PTC thermistors and TVS diodes can effectively manage overvoltage and overcurrent situations.
In addition to these, other interfaces such as RJ45, RS232, micro SD, VGA, and display data lines also need protection. SPSEMI Instant Lightning Electronics provides comprehensive solutions for all these interfaces, ensuring that the entire system remains reliable and secure under various environmental conditions.
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Shenzhen Sichuangge Magneto-electric Co. , Ltd , https://www.scginductor.com