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Editorial Team
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Asked: 2026-05-26T19:37:13+00:00

I bough a cheap RFID reader from eBay, just to play about with. There

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I bough a cheap RFID reader from eBay, just to play about with. There is no API, it just writes to stdin – that it to say, if you have Notepad open and tap an RFID tag to the reader its Id number appears in the Notepad window.

I am looking around for a reasonably priced reader/writer with an actual API (any recommendations?).

Until then I need to knock together a quick demo using what I have, just to prove the concept.

How can I best intercept the input from the USB connection? (and is there a free VCL control to do this?)

I guess if I just have a modal form with a control which is active then I can hook its on change event. But modal forms seem a bit rude. Maybe I can hook keyboard input, as it seems to be injecting like types chars?

Any idea? Please tell me if I cam not explaining this clearly enough.

Thanks in advance for your help.

In the end, I just hooked the keyboard, rather than trying to intercept the USB. It works if I check that my application is active and pass on the keystrokes otherwise. My app doesn’t have any keyboard input, just mouse clicks (and what I read from RFID is digits only, so I can still handle things like Alt+F4. Maybe not the perfect solution for everyone, but all that I could get to work)

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1 Answer

  1. Editorial Team

    Based on your description, it sounds like the RFID reader is providing a USB HID keyboard interface.

    I don’t know if there is anything similar in delphi, but in libusb there is a libusb_claim_interface, which requests that the OS hand control over to your program.

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