Choose portable memory for embedded systems

While most embedded system components are sourced from OEM focused manufacturers, portable memory devices are a grey area. The high-volume consumer electronics market is estimated at £129 billion annually. This creates significant demand for USB flash drives, SD cards and other consumer-focused portable memory devices and for embedded system designers the economies of scale these devices offer can be appealing. However, as Victoria James the PR and marketing director of Nexus GB explains choosing consumer focussed portable memory can be a big mistake.  Here she provides a series of guidelines to follow when choosing portable memory devices for use in embedded systems.

Manufacturers of consumer memory devices are primarily focused on the needs of the fast-changing consumer electronics market and this doesn’t suit the design engineer. In response, a lesser-known category of OEM focused portable memory systems is providing alternatives that meet requirements unique to non-consumer embedded designs.

These two categories of portable memory devices offer unique advantages and disadvantages. The most important thing for engineers though, is how the two categories perform when integrated into embedded designs in commercial, industrial, government, military, medical and other demanding OEM environments.

Typical applications for portable memory in embedded systems include access control and rights management, usage monitoring, data logging, in-field firmware updates and product authentication. The environmental factors and typical usage of the system influence which kind of portable memory solution is the best fit for the application.  

Design considerations – consumer memory
As a result, the potential design considerations for portable memory systems are extensive, ranging from the communications interface/protocol, connector durability, cost and data throughput speed to product life cycle and ruggedness.

Some of these design considerations may be mutually exclusive. For example, small size typically precludes rugged construction. Prioritising these design considerations makes it easier to determine which features are most important for a particular application.

In addition to SD cards and USB flash drives, other consumer memory devices used in OEM designs may include SDHC, microSD and CompactFlash cards. While these NAND-flash-based devices are primarily designed for PCs laptops, digital cameras, mobile phones and MP3 players, the principal benefits that are intended for consumer electronics can also apply to non-consumer embedded devices:

The widespread availability of USB flash drives and SD cards makes consumer memory a convenient option. Most users are already familiar with their operation, and it is easy for OEMs and end users to obtain these devices from electronics retailers.

Another issue to consider is the need for high memory capacity. Transferring data to and from embedded systems often only requires kilobits or megabits of memory capacity, but the higher capacities available in consumer memory devices may be required in some cases. Video logging, for example, can require gigabytes of memory capacity. However, some OEM memory devices are now offered in memory capacities of up to 32GB, so finding devices with high memory capacities is no longer limited to consumer memory.

In terms of costs, the upfront cost-per-bit of most consumer memory devices is relatively low. But if an OEM application requires thousands of portable memory devices over the life of the design, then the expenditure over the lifetime of the application is considerable.

Handheld embedded designs often require a small portable memory device to fit in the system. In these applications, a microSD card may be the most attractive option due to its small size. Equally, some designs may actually require a larger portable memory device. For example, a memory token must be able to be easily inserted and removed by a user wearing arctic gloves in certain military applications.

As you can see, while consumer memory products are not explicitly designed for OEM designs, they do offer unique benefits. However, these benefits may also have unintended consequences.

With hundreds of different models of consumer memory products available, OEMs can’t possibly test, approve and support every device that physically fits. Despite memory manufacturers’ attempts to ensure compatibility, some models will work in an OEM device and others won’t. A lack of control over which devices will work can increase support costs and can be inconvenient for end users.

One must also bear in mind that technology standards change. The transition from SD to SDHC is a recent example. A system designed to use SD cards prior to the release of SDHC will not work with SDHC cards unless the system’s firmware is updated. Likewise, the fast-changing consumer electronics market virtually guarantees that a new technology will emerge in the future, bringing with it new compatibility issues.

Finally, using a consumer memory device may increase the risk of data theft. A misplaced or stolen USB flash drive is not protected from an unauthorised user accessing contained data from a PC, for example. Similarly, using a USB receptacle in an embedded design allows any USB flash drive to plug in, which can increase the risk that information could be pulled off the system or that a virus or other piece of malware could be transferred to the embedded device.

Another drawback is that most consumer memory devices today start at 1GB or higher. As such, embedded systems that require only kilobits or megabits of memory to perform a desired task are essentially paying for capacity they don’t need.

While not always apparent in the early stages of the design process, these considerations should be examined before deciding whether consumer memory meets both the design criteria and the expected use.

Design considerations – specialist OEM focussed memory
Non-consumer, OEM systems are usually manufactured and designed to last years. As a result, portable memory used in these systems must provide long-term availability and reliability. The environmental conditions in which OEM designs operate can be demanding as well, and there is often an increased emphasis on secure access. Requirements that are unique to OEM designs illustrate why consumer memory devices’ light-duty construction, low cycle life connectors, lack of security features and short product life cycles can be detrimental to non-consumer applications.

Rugged construction is another characteristic required by OEM applications, especially for use in harsh environments. Some outdoor applications such as the ones used in the military, construction or agriculture sectors, use portable memory devices to transfer operation and maintenance data between the base and vehicles in the field. The memory device may be exposed to vibration, dirt, moisture, shock, extreme temperature and rough use. Light-duty consumer memory devices and receptacles do not provide sufficient protection or the environmental ratings needed for harsh environments.

Frequent use and long-lasting designs require durable connector systems. Vending machines, for example, may use portable memory to provide cashless vending in non-networked environments. A customer can use the memory device to purchase merchandise from the machine, such as snacks, drinks or even industrial supplies. These machines often see 50-60 cashless transactions per day. Rated at just 1,500 cycles, a USB mating receptacle could wear out in as little as 25-30 days.

Furthermore, many OEM applications require increased security. The widespread availability of devices and systems with USB and SD card interfaces leaves sensitive data vulnerable to data theft and malicious viruses. Accidental data loss and virus uploads have been under the microscope in the Government and commercial sector for some years. In response, some Governments and corporations have banned the use of consumer memory devices to decrease security risks.

Long-term availability for the life of the system is another key issue to be factored in when choosing memory devices. Consumer memory is driven by the consumer electronics market and therefore subject to short product life cycles and frequent obsolescence. Traffic light controllers are an example of long-lasting OEM designs that need a portable memory solution offering long-term availability.