I have been messing around for a little while now connecting my Nexus 7 and various Canon cameras and other devices together, I tried connecting cameras, hard drives and memory cards to various apps free and paid for and these are my findings.
For camera control see this post
I tried numerous cables and kit some worked some didnt
Transferring Data to and from the Nexus7 for Backup and viewing images
The first thing you need is a OTG (On The Go) cable these cost very little the 2 I bought to try (different makes) where £1.25 and £1.29 from ebay including delivery.
You also need a card reader I found the multi card readers I have problematic but that the single card readers where more reliable and also neater to connect without the need for a second cable from the OTG to reader
This card reader worked faultlessly loading the folder list quickly and the data transfer was pretty nippy it cost £2.85 from ebay
I also tried various hard drives and out of the ones I have the only one that would work was the Samsung the others couldn’t get enough power to fire up and just clicked away maybe they would with an additional 5V supply as they had a socket for extra power which the Samsung doesn’t have and thankfully didn’t need that drive also worked nicely.
See update at the end of this post
The program I found the best for transferring files was Nexus Media Importer it just worked all the time and can also be used to stream video and music from attached devices where the other programs where more limited.
Nexus Media Importer https://play.google.com/store/apps/d…ususb.importer Highly Recommended
I also Tried
Nexus USB OTG https://play.google.com/store/apps/d…lemanagertrial
To view the files transferred I used Rawdroid Pro as I had bought the app thinking it could also manage file transfers which it cant but I paid for it and it works fine as an image viewer
other Apps that I checked out for viewing Raw files and you can download and try for free
Rawvision Demo https://play.google.com/store/apps/d….RawVisionDemo
Rawpal Gallery https://play.google.com/store/apps/d…rawpal.gallery
Rawdroid Demo https://play.google.com/store/apps/d…andra.rawdroid
Now what does all the above do
Well it should enable you to review images from your memory card and save to your nexus and then if you dont have the space to store on the Nexus you can then transfer to a suitable portable hard drive or memory stick as a backup till you get back to base
UPDATE re external hard drives
Ok I have persevered with this connection to other devices and the problem with using a portable hard drive.
The biggest issue I thought was supplying enough juice from the nexus to spin up the hard drive as many need more juice than the nexus can supply, I tried all sorts of things and even with a Y cable that has a mini connector for the hard drive and 2 usb male connectors one to go onto the OTG cable fitted to the Nexus and the-other to connect either to a PC USB socket or some power output for USB that connects to the mains that includes the Nexus power supply plug (handy).
What gets it to work consistently is the order in which you connect up and to make things easier I only use the Nexus media uploader app to control things .
Connect the mini usb plug from the y cable to the hard drive and the data end to the OTG socket then connect to the nexus ……….the drive will start to click then plug in the power feed USB plug to a power source and it works ………and it did for me every time.
It looks like to get it to work you need to find out the connection 123 and once you do you are good.
I can now access read and write to all my USB data sources ………..nice
PS the data transfer is pretty nippy as well copied a large 754mb file in 80 seconds and 56 file 95.5MB in 19 seconds