Handheld RFID Scanner for Pets (125Khz/134.2Khz)

Article Date: 21-03-16

One of the common problems you face with pets is that every now and then they get lost. You're then frantically searching Facebook groups and making posts. Only to find your beloved pet gone forever, dead or if you're lucky returned back to you when found.Vets and some police departments have hand-held RFID scanners, which allow you to read the implanted chip within an animal. You can simply buy these ready-made, or if you're into your Electronics and DIY. Have a bash at making one yourselves.

If you find this article useful, and wish to use it. All I ask is that you credit me as the original author and link back to this site, it's low as shit if you steal someones credit, not to mention when you're copying all their hard earned researched and mistakes the least you could do is help them out as a thank you. This was a learning experience which I hope to use to improve my knowledge in multiple fields. I'm building these projects because I want to improve my skills. They're written in the way I worked them out, so they may be confusing and detailed but hopefully it will help others



  1. Fairly simple really. Has to be able to scan the RFID transmitted frequency so that when found, it outputs the unique-ID number of the chip onto a small LCD screen
  2. Device needs to be powered either from an internal (rechargeable ideally) battery. Or from a seperate dedicated battery (9v or AA batteries)
  3. Will need to be able to scan RFID tag - so will need some form of capacitance loop, and also be able to read it. So it will need some form of copper wire, possibly a tag, then it will need a basic BIOS chip to read and output values
  4. Auto shutdown after 2 mins - could be awkward coding, so will probably keep version1 of the device with an on-off switch :)
  5. Beep - audible confirmation that something has been found, maybe with a green or red led


  1. I considered using a Mobile Phone, because a chip is basically an RFID transmitter and NFC on mobiles works the same way. This doesn't work, because NFC works at Ultra-High Frequency (13.6Mhz), and micro chips for animals works at low-frequence (125Khz usually) although now more commonly (134.2Khz). I realise that most of the common ones are being used now, but when looking at the price of products on the web for 134.2Khz for testing a simple design it's just not viable. Whereas once a working product is made, and working theory is understood a lot of components can be reused and simply altered. This intial design is simply to get a working scanner that will detect an RFID tag on the 125Khz range, then output it's "tag" on screen
  2. Ideally the product has to be as CHEAP as possible, whilst being as simple as possible. So that most likely meaning ordering products from China, since most electronics are produced there anyway, I'm in no rush for waiting so I can wait. Ideally try and keep the project within a £30 budget so it's at least the same price or cheaper than an existing one you can buy. Ideally if I have any old materials lying around I'll be using them first to see if I can save some money
  3. Power source. The device will most likely need a 9V battery, as the components will be doing a minimum of 6v power draw. I could run multiple AA batteries in parallel but it's a bit of a mess-on. So I'd rather have one battery doing the job. It won't need a high power source, because all it's doing is scanning and generating the results on the screen
  4. Coding of the RFID tag. I don't understand coding very well, so I may encounter a hiccup which requires research with the tags, once their scanned as to how they are outputted. May need to research basic programming
  5. Reading up on the technology through Wikipedia. The passive RFID implantable tags themselves, don't actually have a power source (well some do, they're powered by Bio-electric fields from the animals). Where as others are simply dumb devices, they only work when within range of the scanner. As the scanner acts as the power source.
  6. Learn exactly how the ID chips work, the 134.2Khz chips seems to comply with the products for the standard. So this means you'd probably need something that could talk with it the equipment which is compliant - ISO11784/11785 FDX-B Compliant transponder. I don't know whether or not I need a specific compliant chip. Or I just need some form of basic chip that is capable of receiving a signal, which then outputs it


These are the below prices for the components I think I will need for the job. The majority of them I will probably be using eBay as it's usually the goto place for projects and sourcing anything cheap as long as you can wait for it. Although I will add in where I souced them from incase there are any custom components required

Item Source Price
16x2 Characters Blue Backlight 1602 LCD Screen Electronic Module Display 5V 1pc eBay £1.68
9V Volt 300mAh Ni-MH Rechargeable Recharge Battery PP3 #9600 NIMH eBay £1.74
SOLID BARE COPPER Round Wire 0.4mm Jewelry Making (26 to 30awg) eBay £2.49
MINI SPST ON/OFF 8mmx13mm Power Rocker Switch eBay £1.14
MB-102 830 Point Solderless PCB Breadboard+Jump Cable Wires 65pcs+Power eBay £2.38
10x Computer PC Motherboard Internal Code Beep Speaker Sounder eBay £1.19
100(Blue White Yellow Red Green) 3mm 2Pin Round Top LED eBay £0.99
EM4100 125KHz Red Door Control RFID Proximity Reader ID Cards Key Fobs 5pcs eBay £2.68
USB RFID Contactless Proximity Sensor Smart ID Card Reader 125Khz EM4100 eBay £3.09
EM4095HMSO16A Transceiver RFID 125kHz 4.1÷5.5VDC SMD SO16 Modulation eBay £8.41
  TOTAL £20.02

If this project is too complex, or you simply wanted to know how to build your own. You can buy a ready made RFID scanner from places such as eBay for around £49.99



OK, this is a bit of a long winded process, because I'm having to understand antenna calculations and induction frequencies. Basically for a 125Khz induction frequency it's recommended you have an Antenna loop with an induction frequency of around 500-1000 nanoHenries. The best way to determine this for me, was by pre-constructing the coil array (loop) first. I decided I was going to have a loop which was 3" in Diameter, and would be approximately 3mm deep.

The formula for working out the Induction is (btw the calculations are in CM) - so 10CM is 0.1CM
L = 0.394 x (Radius x Radius) x (# - Turns x # Turns) / (9 x Radius + 10 x Length)

You can work this backwards, so if you know your determined circle size, a 3" Circle (3mm deep) would have a radius of 3.81CM and a coil depth of 0.3CM. Now that I know the coil information, I need to work out my optimum number of turns for the coil. To get this we multiply 500 (the required nH for inductance) x (9R + 10L) - so (9 x 3.81 = 34.29) + (10 x 0.3 = 3) = 37.29cm

37.29 X 500 = 18,645 (this needs to be what the number hits when the left-hand side is calculated)

We already know the figure of 0.394 and Radius so (0.394 x (3.81 x 3.81) = 0.394 * 14.5161 = 5,719
If we divide 18,645 by 5,719 it gives us = 3260.18 (this is the number we need to reach for # of Turns x # of Turns)

If we get the square root of this it = 57.09 this should be the number of Turns required

So if we apply the formula to the above
L (Coil Inductance in nH) = 0.394 x (R-Squared) x (Turns-Squared) / (9xR) + (10 x L)
This calculates as L = 0.394 x 14.5161 x 3259.26 / 34.29 + 3 = 499.88 nanoHenries (fuck it close enough)


Now that we have our induction frequency of 499.88nH (cough 500) we need to match it with a capacitance. This then allows the loop to resonate the frequency desired. As our loop is going to resonate the frequency of 125Khz we need to work out the required capacitance for this. I used an LC Resonance Frequency calculator for this link below.

Basically fill in the top 10 fields. It will then show you the resonant frequency it will reach with the correct loads.
You know the Inductance (in my case 499.88), basically play around with the top number, and change it unil the resonant frequency gets as close as possible to your target (125Khz in my case)

My calculations are below to what generated my frequency -

Capacitance: 3200 nF
Inductance: 499.88 nH
Resonant Frequency: 125.83 Khz

OK, so in theory we have a working loop. It has the power supply, it has a loop, it's resonating the frequency, but does it need when it's receiving it. We need to output the results to a Decoder. The transceiver produces the code from the modulated signal



The following attachments aren't needed for any part of this project, they're just proof of the level of work I put into this project incase some toospot tries to claim the hardwork I put in was there own and I find out about it. Plus it's also proof of the level of research I did


I'd like to link all the places I had to look up to research or understand these problems. Also I'd like to thank other sites by giving them free plugs if I found their research useful towards helping me solve the problems