GT-511C3 Fingerprint Scanner Hardware, Wiring and Connector Numbering
Created on: 27 November 2014
This article has hardware information on the GT-511C3 fingerprint scanner module and includes wiring, pin numbering (pinout), connector information and voltage levels.
Microcontroller and Arduino connecting information is included with circuit diagrams of 3.3V and 5V interfacing.What Is It?
The GT-511C3 FPS (fingerprint scanner) is a small embedded module that consists of an optical sensor mounted on a small circuit board. The optical sensor scans a fingerprint and the microcontroller and software provides the modules functionality which automatically processes the scanned fingerprint.
The interface of the FPS is very basic consisting of only four pins – power, ground, serial transmit and serial receive.What Is It Used For?
The module can be used in projects for identifying users, for example allowing access through a door by scanning a finger instead of using a key.
Also see Testing the GT-511C3 Fingerprint Scanner Module for a quick test using an Arduino to see if the scanner is working.
Pin Numbering, Functions and Specifications
The image below shows the pin numbers of the GT-511C3 fingerprint scanner.
This image shows the pin functions and voltage levels, followed by more details of each pin.
Pins 1 and 2 are 3.3V TTL pins used to communicate with the FPS module. The default baud rate is 9600bps after power on.
Pin 1 is the transmit pin of the UART on the FPS (UART Tx) and transmits a logic high of up to a maximum of 3.3V.
Pin 2 is the receive pin of the UART on the FPS (UART Rx) and can receive a logic high level of up to 3.3V. The voltage level sent to this pin from a microcontroller needs to be reduced when working with 5V microcontrollers.
Pin 3 is the common GND or 0V pin of the FPS module.
Pin 4 is the 5V input to the FPS module used to power it. This value can be between 4.5V and 6V.
The 4 pin connector on the board is a JST-SH series connector with 1mm pin spacing.
A female 4 pin connector is needed to connect four wires to the FPS for interfacing the module to a microcontroller. Ready made cables can be bought, or a cable can be made by buying a crimp housing and pre-crimped wire leads.
The photo below shows pre-crimped wires that are ready to fit into the JST SH 4 way crimp terminal housing.
The part numbers for the above parts are:
- Crimp socket to free end lead, 150mm – JST part number: SH3-SS5-28150 (RS Components stock number: 311-6647)
- 4 way crimp terminal housing, 1mm pitch – JST part number: SHR-04V-S-B (RS Components stock number: 311-6524)
The cable is made up by simply inserting four crimped wires into the plastic terminal housing. The image below shows the cable made up and plugged into the FPS module.
Two Arduino boards are used to show interfacing with 5V systems (Arduino Uno) and 3.3V systems (Arduino Due).
When connecting to a microcontroller that uses 5V voltage levels on its pins, a level converter must be used to reduce the 5V output from the microcontroller to the FPS module because the FPS module can only handle 3.3V on its UART pins.
A voltage divider consisting of two resistors can be used as a level converter to reduce the 5V incoming signal to 3.3V. The circuit diagram below shows the fingerprint scanner module connected to an Arduino Uno.
The circuit below shows the voltage divider from the above circuit diagram. When the Arduino drives its output pin to 5V, the voltage divider reduces this level to 3.3V so that the fingerprint module is not over-driven.
The actual calculated voltage output from the above divider circuit is approximately 3.283V.
Choosing Voltage Divider Resistors
Other resistor combinations can be used to get a value close to 3.3V output as shown in the table below.
The higher the resistance combination of R1 and R2, the more likely that the communications between the Arduino and SFM will become unreliable due to interference from electrical noise.
The lower the resistance combination of R1 and R2, the more the Arduino pin will be loaded (the lower the resistance, the more current that will be drawn from the pin by the resistors).
Arduino Due / 3.3V Microcontroller Interface
The Arduino Due does not need any voltage level shifting circuit and can be interfaced directly to the fingerprint module as shown in the circuit diagram below.
The GT-511C3 module must still be powered from 5V which is taken from the Due 5V pin.