For more info visit my blog http://zevenwolf.com/blog/category/spring2010/wildlifetracking/
So I was interested in RFID for tracking monkeys. RFID comes in two flavors: passive and active. For tracking monkeys the preferable would be an active RFID chip.
Active vs Passive
Active Power: Battery powered, average 7000 hrs *depending on receiver Signal Strength needed: Low Signal Range: up to 100m Data Storage: 128kb read/write search and access to data
Passive Power: comes from RF reader Signal Strength needed: High signal
Range: 3-5m or less
Data Storage: 128 bytes of read/write
Depending on models active RFID could have high operating temperature, between -35c and 50c. This is important for the high temperatures in the amazon. Another advantage is the size and weight. Ranging around 14 grams and 2.4 in x 1.2 in x 0.4 in to big ones that are around 2in x 3in x 0.5 in
This link is a diy aduino based RFID reader
http://pimm.wordpress.com/2008/03/09/first-rfid-experience-arduino-controlled-parallax-reader/ This is a couple of data sheets from different companies
This link has standard pricing options
My group and I were testing these RF Radios to see if we can make some DIY rfids. These modules are 434 mhz radio transmitter and receiver pairs that run at a range from 2v – 12v. It operates at 2400 baud rate. For more information is located on the sparkfun site: transmitter and receiver.
One of the most important things is the shape of the antenna. Coiling around a 1/2 inch cylinder give a good signal. The receiver is well labeled the only trick is that middle power pin needs to be grounded with a capacitor. This helps smooth out the radio signal coming through. The receiver data pin goes connected to the RX port. For simple tests simply listening to the serial port will give you the transmitted data.
The receiver’s data pin goes connected to whatever you want to send across the link. In this case we are sending analog values via a pot. The data pin is connected to the RX pin.
First we calculate our battery The battery is rated at 3.7v @ 200 mA to make it easier to convert later we turn it into micro volts.
To calculate the Watt hours = voltage * Amps 740,000 micro watt hours = 3.7volts * 200,000 micro amp hours
Now we Calculate the xbee 900 which run at 3.3v: The xbee has 3 modes we have to deal with their consumption: sleep mode: 60 micro amp hours transmit mode: 210,000 micro amp hours receive mode: 80,000 micro amp hours
next is calculating the time ratio We are sending and receiving 100 times a day each takes 1 second thats 200 seconds everyday 73,000 seconds 31,556,926 seconds in one year 73,000 secs/31,556,926 secs = .002 the xbee is transmitting and receiving during the year
We have combined the 2 events so we can average: 80,000 micro amps and 210,00 micro amps = 135,000 micro amps
Now that we have a time ratio we calculate (.002)(3.3volts)(135,000 micro volts) + (.998)(3.3volts)(60 micro volts) = 740, 000 micro amp hours The right side of our calculation gives use Watts and the left gives us Watt hours
891 watts + 197 watts = 740,000 micro amp hours 1088 watts = 740,000 micro amp hours 740,000/1088 = 680 hours or 35 days on one battery we need this to last at least a year and a half That will be 27 batteries but we’ll need closer to 36 batteries to be safe
The most important number is that for a year and a half we need more then 3600 milliamps at 3.3v