Regarding the reading distance of low-frequency cards

一沙一世

Regarding the reading distance of low-frequency cards [Copy link]

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A low frequency card T5577 and its card reader, as shown below

Now I have two problems

1. When the card is placed against the card reader, the operation direction must be swiped horizontally from right to left (in the direction indicated by the red arrow in the figure below) to between the two black vertical lines (1) and (2) in the figure, the card can be recognized normally. However, if it is moved to the left beyond the black vertical line (2), the card cannot be recognized. What is the reason? It should be that the card reading effect should be better if the card covers the entire card reader?

2. If you stick the card directly on the top of the card reader (in the sky direction), the card cannot be read normally. However, if you put a 12mm thick plastic shell on the top of the card reader, the card can be swiped successfully no matter from left to right, from right to left, from top to bottom (horizontally up and down), from bottom to top (horizontally up and down), in short, from the horizontal direction, or from the sky to the ground vertically from top to bottom, and finally put the card on the plastic shell, but the thickness of the plastic shell cannot be less than 8mm, otherwise the card reading will always fail. What is the reason for this?

wangerxian

Is it that the closer the distance, the more problems there are? When I tested NFC card swiping, I found that there is a blind spot in NFC scanning. But it is not as obvious as yours. Take apart the card reader and let me check the antenna.

一沙一世

wangerxian posted on 2022-7-4 13:17 Is it a problem when the distance is close? When I tested NFC card swiping, I found that there would be a blind spot in NFC scanning. But it is not as obvious as yours. I took apart the card reader and saw...

Thank you so much.

wangerxian

Yishayishi published on 2022-7-4 14:27 Thank you very much.

[The thickness of the plastic shell cannot be less than 8mm], try to see how thick it can be for the card to be detected.

一沙一世

wangerxian posted on 2022-7-4 14:32 [The thickness of the plastic shell cannot be less than 8mm]. Try to see how thick it is and how much the card can still be detected.

Thank you. Maximum distance: 21mm

wangerxian

Yishayishi published on 2022-7-4 15:05 Thank you. The maximum distance is 21mm

You can try to use this card to test and see what the result is.

一沙一世

wangerxian posted on 2022-7-4 15:57 Try using this card to test and see what the result is.

OK. Thank you very much. Could you help me analyze the causes of problems 1 and 2 above?

chunyang

This is related to the coupling design of the antenna, and it is impossible to analyze without specific information. It is recommended that you use a storage oscilloscope to capture the card's sensing conditions under different working conditions, including the corresponding data output of the card reader. Only with specific information can you start the analysis.

一沙一世

chunyang posted on 2022-7-4 16:26 This is related to the coupling design of the antenna. It is impossible to analyze without specific information. It is recommended that you use a storage oscilloscope to capture the induction of the card under different working conditions, including...

Thank you very much. Does the storage oscilloscope store pictures one by one? If I want to study it, I have to connect these pictures one by one to see the effect?

chunyang

Yishayishi published on 2022-7-4 19:01 Thank you very much. Does the storage oscilloscope store pictures one by one? If you want to study it, you have to connect these pictures one by one to check...

No, it is not such a stupid method. Simply store the sampled data directly. Naturally, there is no picture connection. Just call out the stored results directly.

wangerxian

Yishayishi published on 2022-7-4 16:05 OK. Thank you very much. Can you help analyze the causes of 1 and 2 in the above questions?

There are blind spots in NFC antenna scanning. Judging from the phenomenon you mentioned above, it seems that the distance is too close and it cannot be scanned.

Swipe horizontally from right to left can be detected, but what about other directions? From top to bottom, from bottom to top, etc.