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SD card enables low-cost Wi-Fi connectivity in digicams

Posted: 02 Oct 2009 ?? ?Print Version ?Bookmark and Share

Keywords:Wi-Fi? SD card? digital camera?

Power concern
The honeymoon phase faded a bit once the flashing red low-battery indicator appeared on the camera's LCD. My primary concern going into this experiment with the Eye-Fi Wi-Fi card was the impact it would have on my camera's battery life and the red flashing light was confirming my fear. Since I didn't place a fresh set of AA batteries into the camera prior to the test, it wasn't fair to place all of the blame on the newly inserted Wi-Fi card. The only way to truly understand the impact of transmitting each photo via Wi-Fi was to bypass the power supplied by the four AA batteries and connect the power and ground leads of the Wi-Fi card to the Portelligent source measure unit while inserted in my camera.

The power consumed by the Eye-Fi Share card could then be compared, using the same methodology, against the power consumed when storing the picture on a standard SD memory card.

With the camera in standby or turned off, the Eye-Fi card consumed an average of 72mW while keeping the onboard Wi-Fi in a low-power mode pinging for a Wi-Fi host. Brief power spikes of 585mW every 60 seconds indicated the Eye-Fi was attempting to keep an active connection with an access point. The standby power consumed by a standard SD memory card was less than 1mW with a brief spike to 30mW at camera startup.

After taking a picture with the Eye-Fi installed in the DiMAGE Z2, the camera LED, indicating the image was being stored to the 2Gbyte of NAND memory provided by a Samsung K9LAG08U1M, blinked for approximately 15 seconds while saving the 1.7Mbyte picture. Data flow from the camera to memory and memory to Wi-Fi is managed by a Hyperstone S4-LDK01 flash memory controller. The average power consumed during the save to non-volatile memory was 170mW on the Eye-Fi card. The same resolution image stored on a standard SD memory card took approximately 2.5 seconds with an average power consumption of 44mWa far lower total integrated power for the simple act of storing an image.

Once the picture was captured and stored in the non-volatile memory, the Eye-Fi manager located in the Windows system tray began blinking indicating communication between the Eye-Fi card in my camera and my laptop. Nineteen seconds later, the image I captured with my camera appeared in a small window on my laptop with a percent bar. According to the status bar, the 1.7Mbyte image required approximately 39 seconds to transfer from the camera to the laptop at a rate of 45KBps.

Examining the power consumption results from the source measure unit reveals the Wi-Fi chipset, an Atheros AR6001G-BC1E ROCm (Radio-on-a-Chip) mobile WLAN solution combined with an Epic FM2422 2.4GHz front-end module, consumes an average of 160mW over a 75-second time period (19 seconds setup, 39 seconds Wi-Fi transfer, 17 seconds closing operations) during an image transfer. All ICs, including the memory components, are single-side mounted on a Wintec PCB with a 2007 date stamp. Again this total power consumed for wireless transfer is an additional burden on the camera battery over traditional card-based download.

- Jeff Brown
TechOnline

For application notes on SD cards click here.


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