I'm working on a project to create a cat feeder. classic one. This one will have a door that opens based on an rfid tag in the cat collar.
I am using an RDM6300 that works well in a range of about 3cm, but my cat was not smart enough to know where to move to make it read its tag.
Now I am exploring the idea of using a bigger antenna where the cat pass his head through and it reads the tag, I saw similar online.
I tried building the antenna with a 17cm radio and using this calculator Multi layer air coil design and calculator, targetting 475uh and a 32 gauge cable. It says I should do 38 turns. I built the antenna and won't work.
Just for testing I built a smaller antenna, 6.5cm, 63turns, this one worked without problem.
I wonder what I am doing wrong with the bigger antenna? I 3D printed a place to wrap the wire around (see image).
Please consider I am quite new to electronics. I covered my basics, such as making sure the cables I soldered to the end of the copper wire are properly conducting from one side to the other. I also tried unwiring 3 to 6 turns to see if it improves. but no luck.
Unfortunately, your antenna actually REDUCES the field strength needed by the cat's RFID device. If you quadruple the area of the antenna you need to quadruple the power going to that antenna to maintain the original field strength.
This is exactly the one I am getting inspiration from. I didn't know the guage could had such a big effect. I'll try to get a 24 one. Thanks for the tip.
Edit: I am already using enameled wire but higher gauge.
An RFID for your cat is powered by the signal it receives from your antenna coil. When sufficient power has been received to power it's transmitter, it switches and transmits back to your coil. With similar timing, your transmit unit must switch from transmit to receive in order to receive the ID signal from the cat. IT is a very precise dance being done by the two devices.
If the cat device cannot receive enough power to store so it can transmit, your device will never receive a signal, because one it never produced.
The power your device transmits to the cat is ONLY produced by the IC chip in your device, There is NOTHING you can do to change that power. A higher voltage will destroy the IC.
The try to increase the reading range depends entirely on the transmission of power to the cat device.
The antenna must be RESONANT at the frequency being used so it can produce the strongest field. From what I have read you do not have any equipment that can tell you when the antenna's resonant frequency. Look for a "field strength meter" that can be tuned to the RFID frequency. When you have one, you can make adjustments to the antenna so it produces a maximum field strength.
On further thought, the signal being transmitted is quite short in length and is not transmitted very often. So what is called an "antenna analyzer" would be more appropriate. It can tell either through a meter or graphically point to the primary resonant frequency of your antenna. What is the frequency being used for your cat RFID?
But your RFID uses a frequency of 125KHz totally the other end of the EM spectrum.
From the look of the bit of the picture where you can see the antenna you are trying to build it looks like a Yagie . For the frequency of your RFID reader the elements should have to be many yards long.
No that only happens with higher frequency RFID tags. With this one the tag switches a load resistor on and off across the coil. The transmitter "feels" the load change and generates a signal from it.
When trying to get an RFID reader through FCC compliance they kept asking me what frequency the tag transmits on. I left the box on the form blank and they kept asking me. Eventually I had a chat to them on the phone from the UK. They then apologised saying that they were so use to other RFID tags, they forgot that this type didn't retransmit anything.
Yes in general, but if you get the antenna at exactly the resonant frequency it will not work at all. For best results you set the antenna resonance about 5Hz to one side of the frequency of the transmitter. Not many people, know that, I think I discovered it.
I have discovered if I REALLY want to know how it works, I must purchase a copy of the ISO documentation But your description provides the basis for the operation. Thanks!
