After doing several tests with the device I had several findings that are worth noting. The first is the radius and that putting a tag either side of the board produced a better radius range result than putting on the edges of the board. The max radius was approximately 6cm - 6.5cm away from the device. From the edge of the reader it was about 3cm until the string appeared. In addition to this, the speed at which the tag travels across the reader is also important, as if it goes across it too quickly, it will not be recognised. The suggested speed of the tag to cross the reader is of at least 50ms. As this technology will be used in a cat feeder that will need to feed 2 cats, it was important I tested how the reader responded to multiple tags within its range. My results showed that the device could not handle more than one tag at a time as the id string would simply disappear once there was another tag added to a single tag - this is unlikely to be an issue with feeding two cats due to the small range and constant movement of the cats - but for more animals/tags this is more likely to be an issue. I researched into this and came across multiple sources suggesting that it is possible, and that anti-collision methods can be in place to do so. It may seem as if the reader I am using does not use these methods and therefore cannot detect more than one RFID object at once.
Along with the id string provided from reading each tag was the protocol used for each object read. For the tags used, the protocol EM4100 was in place. After researching this, I came across what the format of the protocol. The tags I used with this protocol have 64 bits of ROM, meaning it's data cannot be changed.
For my project, it will be important that the device can be controlled using the raspberry pi and the device tested supports linux and many porgrammng languages (including C# and java). This means I can use the devices API to control and read it's operations. The Phidget 1023 RFID reader seems to be a suitable choice to use in the cat feeder.
By Jonathan Grant
References:
http://www.phidgets.com/docs/1023_User_Guide
http://www.priority1design.com.au/em4100_protocol.html
https://www.wewear.org/assets/1/7/RFIDBasic_Paxar.pdf
