Electronic Design

Create A Smart Cable To Ensure Quality Control And Authentication

A quick search of the Internet reveals that cloned or knockoff cables are a growing problem. Common complaints from cable users documenting this problem include intermittent signals, poor long-term reliability, and complete malfunctions. These complaints are the result of cheap wire, improper contact plating, incorrect wiring, and poor quality control.

Electronic instruments alone provide no easy way to tell the difference between a genuine cable and an inferior counterfeit version. However, one solution is to embed an electronic (1-Wire) chip in the near end of the cable to create a smart cable (Fig. 1). This example uses the DS2431 to illustrate the technique, but other 1-Wire devices may be more appropriate for specific applications (Fig. 2).

An IC with a 1-Wire interface merges its power-supply voltage and communications on one pin.1 For typical smart-cable applications, the chip contains a unique identification number plus user-programmable memory, which can be secure memory or a write-protected EEPROM.

The far end of the cable connects to a sensor, peripheral, accessory, or other equipment. If the equipment already contains a microcontroller or equivalent (such as an FPGA), you need only add a pullup resistor for the 1-Wire line. A spare I/O port and the memory space required for firmware enhancements are often available in the system, at no extra cost.

When a smart cable is plugged in, the 1-Wire chip generates a presence pulse that the microcontroller interprets as an attachment event. If the connection is made while the microcontroller is switched off, then upon wake-up the MCU generates a reset pulse on the 1-Wire line and tests for a presence pulse. If the MCU doesn’t detect a presence pulse, the device “knows” that either no cable is plugged in or the cable is counterfeit.

If the MCU detects a presence pulse, it reads the 1-Wire chip’s identification number. (For some applications, it may be sufficient to verify that the ID number falls within a certain range.) The MCU usually reads the chip’s data memory as well, looking for an electronic description of the product (for instance, the cable, the sensor at the far end, or both).

For a cable with a sensor, the stored data may include the manufacturing date, revision, configuration, calibration data, and expiration date. You achieve the highest level of authentication (detection and rejection of a clone) by using a secure memory that supports challenge and response authentication.2 Thus, a 1-Wire chip, which occupies only one dedicated pin in the cable, can add functionality, ensure quality, and provide aftermarket protection.

1. Linke, Bernhard, “Overview of 1-Wire Technology and its Use,” Maxim Integrated Products, 2008; www.maxim-ic.com/appnotes.cfm/an_pk/1796.

2. “Protecting the R&D Investment: Two-Way Authentication and Secure Soft-Feature Settings,” Maxim Integrated Products, 2005; www.maxim-ic.com/appnotes.cfm/an_pk/3675.

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