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Sorry it may seem stupid but I think my confusion is drifting me away from the solution so I wanted to ask.

I am trying to build a fixed RFID reader. But the project has some other complex work to be done, so I am using a mini PC as the main hub.

I need to connect an RFID reader through a port on the PC (there are RS232, Ethernet and USB) I am trying to select the cheapest solution for the reader module I have found. This is the RFID reader module I want to use but the thing is I am confused with the Fixed RFID readers with this module/the development kit and the RFID reader module.

Datasheet says there is a serial port on the module I have linked. If I just, say, connect this serial pins directly to RS-232 and use the API (which is compatible with the OS) will that be enough?

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  • \$\begingroup\$ either that or the usb port which is way more popular nowadays than rs-232 on pcs \$\endgroup\$ – Wesley Lee May 25 '16 at 9:25
  • \$\begingroup\$ So in practice, I don't need anything else than this module I have linked? \$\endgroup\$ – Batu Yıldız May 25 '16 at 10:08
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    \$\begingroup\$ @BatuYıldız - Note that if you choose to use the serial port on that RFID module, it must not be directly connected to your PC's RS-232 serial port. That would likely cause damage to the module. Information on the datasheet is limited, but the serial port on the module is described as some variant of logic-level UART interface and is therefore not suitable for direct connection to an RS-232 port (e.g. on a PC). Their development kit for the module might offer a genuine RS-232 connection - you would need to get more details from the manufacturer/supplier regarding that. \$\endgroup\$ – SamGibson May 25 '16 at 10:51
  • \$\begingroup\$ You should wait a while, like a day, before accepting a answer. Most people will skip over a question with accepted answer, so you won't know what others might have said. \$\endgroup\$ – Olin Lathrop May 25 '16 at 11:14
  • \$\begingroup\$ Right, not used to the system sorry. \$\endgroup\$ – Batu Yıldız May 25 '16 at 11:26
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It looks like the module can talk either serial or USB. I didn't see any mention of Ethernet in the quick writeup.

Either will work, and there are issues both ways.

RS-232

The serial will need a converter that goes between the logic level signals of the module and the RS-232 signals of the PC. There are chips that do this, so this is no real issue if you are making your own PCB anyways. For more details, see the RSLink2 product that I sell. That page also links to the datasheet of the converter chip used in the product (Yes I know google complains about that page. It's a false positive. There is no malware on our site.).

In software, you communicate via a COM port. Your application can directly talk to the device. There is no library or driver needed. However, you need really good specs on the serial communication protocol.

USB

Electrically, USB will "just work". In this case, the complication is in the software. A driver in the OS for the device will be needed. If the company supplies you with a driver and then gives you proper specs for calling it, then this may be the best solution. However, in my experience a lot of such drivers are of questionable quality and they almost never give you proper specs to communicate with the driver.

Usually you get a host library and a driver as one package. That by itself is reasonable enough, but often, even usually, the library is of poor quality and the documentation no better.

Some hardware vendors will add USB support by slapping on a FTDI or equivalent chip to a existing serial interface. That gives you the worst of both worlds. You still have the issue of knowing the COM port, and you don't get the inherent device ID and enumeration features of USB. If USB is supported as a afterthought like this, you might as well connect directly to the real underlying serial port.

Conclusion

Electrically, USB should just work and RS-232 can be made to work easily enough. The decision comes down to how good the documentation of the low level protocol, the driver interface, and the library interface are. Have a private talk with a field engineer and try to determine how solid each interface is, how the company plans to proceed in the future, a honest assessment of the driver and library quality, etc. And of course ask for all the documentation up front and read it carefully from the point of view of writing a embedded app trying to drive this device. That alone may dictate one interface over the other.

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This device is USB 2.0 compatible. This means that you can connect it directly to your PC via USB. I have no access to the datasheet, however the fact that the maximum speed is 12 Mbps makes me believe that the device is interfaced through an FTDI chip; if I am right you can send/recieve data from the module using the serial port (RS232/Uart), this can be done easily using most programming tools.

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    \$\begingroup\$ 12 Mb/s is merely the "high speed" USB standard. It has nothing to do with a FTDI chip. \$\endgroup\$ – Olin Lathrop May 25 '16 at 11:05
  • \$\begingroup\$ I did not say that it is the USB speed. 12Mbps is the maximum baud rate for FTDI chips working in UART mode. \$\endgroup\$ – Adam Z May 25 '16 at 11:07
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    \$\begingroup\$ Again, that's the maximum for "full speed" (oops, I said "high speed" before) USB, having nothing to do with FTDI. 12 Mb/s is the fastest any "full speed" USB device can go. The USB 2.0 spec allows "high speed", which is much faster, but you only need to support the 12 Mb/s "full speed" mode to be USB 2.0 compatible. Many USB 2.0 devices can only do 12 Mb/s. This is not a indication of a FTDI or any other specific chip being used. \$\endgroup\$ – Olin Lathrop May 25 '16 at 11:13

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