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I'm working on designing a PCB to allow two Wiegand HID card readers to be connected to a single control board using digital isolation IC's and wanted to make sure the IC's and other components are adequate for the job and if there is anything else I may be missing.

Each card reader only uses four signals, CARD PRESENT, BEEPER, DATA0, and DATA1, which will get wired into two terminal blocks (J1 and J2). From here, the signals are connected to discrete inputs on the digital isolation IC's: an SI8640AB-B-IS1R for 4 of the signals and an SI8631BT-IS for the rest. The outputs on the IC's are then tied together so whichever input of a pair is triggered, a single output will be activated, ex: DATA1_A and DATA1_B are on inputs A1 and A2 and the corresponding outputs, B1 and B2 are tied together as DATA1 which gets sent to the controller.

The BEEPER signal coming back to the card readers is fed into two AND gates along with the CARD PRESENT signal which will route BEEPER to the correct reader being used.

(Click image below for larger version)
schematic

Original schematic PDF link via Sharepoint

Si86xx Data Sheet

SamGibson
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Seth Koberg
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  • You can't just connect output signals together - they'll fight each other and maybe neither will win. – Finbarr Dec 02 '20 at 15:59
  • @Finbarr: The card readers will never be used at the same time: one will be located ~10 feet in the air, the other ~5 feet in the air, and its my understanding that the Wiegand protocol won't do anything with signaling until a card is nearby. If that does pose an issue, though, how would you suggest mitigating the problem? Some sort of disconnect from one card reader while the other is in use? – Seth Koberg Dec 02 '20 at 22:15
  • None of that means it's possible to just connect outputs together, you need to learn a lot more about the protocol and how it works so that you can use the correct logic to combine them. Why use isolation ICs anyway? The readers are completely self-contained, aren't they? – Finbarr Dec 03 '20 at 00:07

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