Interfacing Fingerprint Sensor (R307) Identification / RFID with STM32 Blue Pill

Fingerprint Sensor (R307) practical reference

The R307 is an optical fingerprint reader module from Hangzhou GROW Technology, built around an integrated optical sensor and an onboard DSP that handles image capture, feature extraction, and fingerprint template matching entirely on-module. Rather than sending raw images to your microcontroller, it does the heavy lifting itself and returns simple pass/fail match results over a UART packet protocol (0xEF01 header, 4-byte address, checksum), making it a popular choice for DIY smart locks, biometric attendance systems, and secure-access add-ons for existing projects. Per the manufacturer's manual it draws a modest 50mA typical, images a finger in under 0.5s, and can store up to 1000 templates with sub-1s 1:N search across the full library.

Key specifications

• Sensor type: Optical fingerprint sensor with onboard DSP/processor — handles image capture, feature extraction, template generation and matching entirely on-module
• Operating voltage: DC 4.2V–6.0V (5V typical) — per Hangzhou GROW R307 datasheet
• Operating current: Typical 50 mA (datasheet-rated; some resellers list higher figures — 50 mA is what GROW's own manual specifies)
• Interface: UART, TTL logic level, default 57600 bps (configurable 9600–115200 bps in 9600 bps steps) — or USB 2.0 on modules that break out D+/D-
• Image acquiring time: < 0.5 s
• Matching modes: 1:1 verification (match against one specified template) and 1:N search (match against the whole library)
• Template / library storage: Up to 1000 fingerprint templates in onboard flash; 512-byte template size, 256-byte character file size
• Security level: 5 grades, set via SetSysPara (1 = lowest FRR / highest FAR, 5 = highest FRR / lowest FAR)
• False Accept Rate (FAR): < 0.001%
• False Reject Rate (FRR): < 0.1%
• Average search time: < 1 s across a 1000-template library (1:1000)
• Sensing window: 19mm x 21mm
• Operating / storage environment: Operating: -10℃ to +40℃, 20%-85% RH; Storage: -40℃ to +85℃, <85% RH
• Dimensions: Module: 44.1 x 20 x 23.5mm, split-type optical housing

Pinout and connection notes

The module ships with a 6-pin JST connector carrying VCC, GND, TXD, RXD, TOUCH and 3.3V (the last two power and read the capacitive touch/wake circuit, not the main module). Per GROW's datasheet the module needs 4.2V-6V on pin 1 to operate reliably — running it purely off a 3.3V rail is under spec even though the UART lines themselves are TTL level. On 5V boards like the Arduino Uno you can wire directly; on 3.3V-only boards (ESP32, STM32) power the module from a 5V rail but consider a level-shifter or divider on the module's TX line feeding back into the MCU's 3.3V-only RX pin.

• VCC (5V): Power input, DC 4.2V–6.0V (5V typical)
• GND: Ground, common with power ground
• TXD: UART data output, TTL logic level — connect to microcontroller RX
• RXD: UART data input, TTL logic level — connect to microcontroller TX
• TOUCH: Finger-detect output signal (max 50mA drive) — goes active when a finger touches the sensor window, useful for waking a sleeping MCU
• 3.3V: Power input for the touch/finger-detection circuit only (DC 3.3V–5V, ~5µA) — separate from the main VCC supply on pin 1

Integration checklist

1. Confirm the exact part number and breakout-board revision.
2. Verify supply voltage, current demand, logic levels, and signal direction against the datasheet.
3. Check controller pin assignments and bus address or interface mode against the example code.
4. Power up with external loads disconnected, then test signals before full integration.
5. If readings or communication fail, check power and ground first, then pin mapping, interface settings, and library initialization.

Troubleshooting and reproducibility

Record the board used, wiring, library/version, supply arrangement, and measured behavior. Use the selected board-specific wiring example as the source of truth. Never assume visually similar modules share identical voltage tolerance or pin order.