Review of Tangxi Smart USB UHF RFID Reader 915Mhz
TLDR summary: Not much documentation, works as a USB keyboard and emits the contents of tag EPC memory (hex encoded) plus a newline, decent sensitivity, seems very hackable if you are into that kind of thing.
The box contained nothing other than the reader and a mini-USB B to USB A cable.
The reader enclosure can be opened easily by removing 4x 10 mm foam pads at the bottom and unscrewing some self-tapping Phillips head screws. The enclosure measures 64 mm x 105 mm x 13.5 mm. The board inside is slightly smaller at 60 mm x 100 mm x ~9 mm. A large portion of the height of the board is occupied by two LEDs (one blue, one green) inside a large flat diffuser. If desired, the board could be stripped down by removing the antenna/LEDs/beeper and cutting a large empty part of the PCB off, resulting in dimensions 60 mm x 46 mm x 5.1 mm.
The board is essentially a MagicRF M100 module attached to an antenna and an STM32F103 clone, which emulates a USB keyboard and in my testing emits a 96 bit (24 character) hexadecimal string which I assume is meant to represent the contents of the EPC memory. The tags I tested with were ISO 18000-6C tags with 96 bits of EPC memory. When reading a tag, the green LED illuminates (the blue LED is always illuminated while the unit is powered). Additionally, a beeper will sound when the tag is read.
I found that the detection range is about 3-4 feet, though I did not test this rigorously. It was almost annoyingly sensitive for purpose of scanning many tags to determine their EPC contents. I could not find any way to decrease the output power / detection sensitivity without hacking the device entirely, despite the claim that the output power is software adjustable.
Note that there is a male Hirose U.FL antenna connector on the board, which should facilitate the attachment of an external antenna, amplifier, or attenuator if desired. I checked and it is indeed connected to the primary antenna, which would likely need to be desoldered for this usecase.
If oriented as in the photo, the 4 pin 0.1" header holes are connected to (from top to bottom):
- Ground
- PA14 (SWCLK)
- PA13 (SWDIO)
- VDD
These should allow reprogramming using the SWD interface with an appropriate STLink programmer or similar.
The two LEDs are connected to pins PB8 and PB9. The USB connector D-/D+ is attached to pins PA11 and PA12. The buzzer is attached (through a MOSFET) to pin PB4. The MagicRF module appears to have the same pinout as the reference design shown on the MagicRF website. The TTL_RXD and TTL_TXD pins on the MagicRF module appear to be connected to PA9/USART1_TX and PA10/USART1_RX respectively.
The purpose of the HF600 chip and the unpopulated IC footprint are a mystery to me.