Introduction: Disabling a ‘Tesco’ Contactless Credit Card and Other Contactless Cards
Due to an attempted fraudulent activity on my Tesco credit card, I had to be issued with a new one. But when it arrived, I was extremely angry to find this was a ‘contactless’ card, which I had never requested and absolutely did not want under any circumstances with its’ known security issues. Particularly so, as I had enough hassle with the security breach on my original card, without adding a whole new way to at least double the chances of it happening again!!
I contacted Tesco Bank and requested a standard card, but found that their ‘customer service’ wasn’t as high on the agenda as it should have been, as 'contactless' was the only type of card they were issuing now. Therefore, I had two options, cancel the card or, (as I had nothing to lose) try to find a way to ‘neuter’ the contactless circuity, without messing up normal chip & pin payments.
Step 1: The Result: One Neutered Tesco Credit Card
I carried out an Internet search and found the article by Jayefuu on here, who used a Micro-CT scanner to locate the antenna tracks. Unfortunately, making a cut in the bottom right corner of the Tesco card did nothing (and I nearly ended up making a contactless payment when I tested it!), it only demonstrated that there is no ‘standard’ way to run the tracks inside the card. Therefore, as I didn’t have access to any form of X‑ray scanner, the only obvious solution was to build a low power13.56 MHz signal generator and use it to locate the antenna tracks on the Tesco (or any other card).
This is obviously not going to be accurate as using a CT scanner, but it located the antenna tracks on the Tesco card, so they could be cut in a safe location without risking damage to the chip or magnetic strip, as can be seen from the photos.
Step 2: Contactless Card Antenna Locator and Broken Track Simulator
The circuit is a standard 13.56 MHz oscillator using the unbuffered 74HCU04 CMOS chip and the output is buffered to drive a 13.56 MHz filter and L2 the pink transmit antenna.
1. L1 was a convenient inductor that I had and the 13.56 MHz crystal was a
surface mount type that I purchased from Ebay.
2. L2 is fairly small and rectangular, so that it can fit inside the card antenna when the card is placed in line on top.
Set up is simple: Tune VC1 for maximum DC output on M1 (about 13V on my set up). The power output of this circuit is insufficient to power the chip on the card, so placing a contactless card over the pink transmit antenna (orientated in line with it) will cause a large drop in DC voltage when card is centralised over the transmit antenna. Moving it around will allow the location of the card antenna boundary to be located.
The Broken Track Simulator: This is useful for testing the correct function of the circuit and its’ antenna is approximately the same size as a card antenna. When placed over the transmit antenna with S1 closed, there will be a large drop in DC, simulating a standard contactless card. Opening S1will only give a few mV drop, simulating a neutered card.
Once the card antenna tracks have been located, a fine saw cut in a safe location should finish the job, which can be confirmed as outlined above.
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