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RFIDuino - Appendix B: Read Range



The read range on your RFIDuino is not absolute - many factors will effect how far you can reliably read a tag from. But why is this? Why can some setups read tags past 100mm, and some need almost physical contact? The main considerations you'll need to consider are Antenna Size, power, and Materials/Interference

Antenna Size, Tag Size and Orientation


A larger antenna on either the reader side or the tag side will increase the read range of the the RFId system. The RFIDuino comes with an antennna that has a fixed size, but by picking the size of your tags you can increase the range of your RFID system. Generally, the larger the tag, the greater your RFIDuino's read range will be. As you can see in the table below, a large tag like our thick clamshell cards can read from a much farther distance than our 18mm buttons.

RFIDuino Read Range* (mm)
Power Supply 18mm Button Key Fob Thick Card
12v DC 45 70 105

All of our readings assume that the two flat antennas are parrallel to each other. Trying to read a tag at an angle is possible, but read range will diminish as the that angle reaches 90 degrees and puts the tag and reader on the same plane.

Power


To get the best read range out of the RFIDuino, you will need to make sure it has adequate power. A USB connection, which can only supply .5A, can power the RFIDuino, but not to its full potential. As the table below shows, using the RFIDuino with a power supply or battery can greatly increase its read range.

RFIDuino Read Range* (mm)
Various Power Supplies
Power Supply 18mm Button Key Fob Thick Card
5v USB 25 40 65
6v DC 40 68 102
12v DC 45 70 105
9v Alkaline Battery 50 75 115
7.4v LiPo Battery 50 75 115

As you can see, increasing supply power wil increase the RFIDuino's read range to a point. When you are feeding an Arduino power through Vin (like with a battery or DC power supply), you are running your power through a regulator. A regulator takes higher voltages and steps them down to lower voltages, in this case it will take anything from 6-12v and step it down to 5v. There is a limit to the ammount of current a regulator will supply, as well as a limit to what the RFIduino needs to operate at peak efficiency.This is why the read ranges on the RFIDuino when powered through Vin are so similar. Some regulators behave differently at different voltage inputs. For example, the regulator on a Seeeduino v3 board supplies very little current at 6v, so you are better off with a 9v or 12v powe supply. You will also have to consider the power needs of any other devices on the board - any additional devices attached to the RFIDuino will draw power and this power drop can reduce the read range of the RFIDuino.

Materials/Interference


For most applications of RFID, you will want to encase your reader, tag, or both in an enclosure. Some materials may lower the strnegth of your RFID signal, or even totally block it out! Because RFID works using electromagnetic waves, materials that absorb electromagnetic waves can lower the read range of your reader. Generally, nonconductive materials like wood and plastic have very little effect on the read range of an RFID reader. Conductive materials like metals and saltwater can have a significant effect on the read range of an RFID reader.
RFIDuino Read Range* (mm)
Various Materials, 7.4 LiPo Battery
Power Supply 18mm Button Key Fob Thick Card
Nothing (Air) 50 75 115
7mm Wood 49 72 110
50mm Book na 51 110
4mm aluminum plate No Read No Read No Read
4mm stele plate No Read No Read No Read
1mm steel mesh 15 35 55

Interference can also be caused by other devices emmitting electromagnetic waves. Other RFID readers and other devices's operation may interfere with the read-range of your reader. This interference can be picked up by both your RFIDuino antenna and the connector cable between the antenna and sheild. Twisting the cable or wrapping it in foil to add shielding can reduce outside interference.



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*These tests were performed with an Arduino Uno running a modified version of the Hello World 2 sketch.

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