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World’s first fingerprint sensor HAT uses capacitive scanning

Dec 1, 2020 — by Eric Brown 813 views

SB Components has won Kickstarter funding for a $60 “PiFinger” HAT for the Raspberry Pi featuring a 2D capacitive fingerprint sensor with 176 x 176 resolution that can detect, compare and register up to 24 fingerprints.

UK-based SB Components, which has delivered ambitious, Raspberry Pi based products such as its PiTalk phone, LapPi laptop, and PiArm robotic arm, has weighed in with what it calls the world’s first fingerprint sensor HAT. The open source, $60 PiFinger has won Kickstarter funding and will ship in February.

PiFinger and detail view
(click images to enlarge)

Available for order through Dec. 24, the PiFinger can also be purchased in a $100 package that bundles a Raspberry Pi 4 with 2GB RAM. A $107 package bundles the HAT with a 5-inch, HDMI connected screen and a $134 package includes both the RPi 4 and display.

The PiFinger incorporates a Cortex-M23 based Nuvoton MCU with on-chip crypto-accelerator, as well as TrustZone and XOM memory protection security technologies. The HAT provides an active 2D capacitive scanning area of 8.8 x 8×8 mm and a resolution of 176 x 176 pixels with 408 dpi spacial resolution.

PiFinger connected to Raspberry Pi via USB (left) and via GPIO
(click images to enlarge)

Software is available that lets you compare and register up to 24 fingerprints. Functions include fingerprint storage, scan, comparision (1:1), and search (1:N).


Although the PiFinger is listed as an open hardware project, SB Components has yet to identify the sensor, which offers 8-bit pixel value and 256 gray levels. The sensor communicates with the MCU via high-speed a SPI interconnect, helping to enable up to 2-megapixels per second capture speed.

PiFinger communications diagram
(click image to enlarge)

The MCU links up to any 40-pin Raspberry Pi via a USB 2.0 full speed UART-to-USB converter expressed via a micro-USB port. Alternatively, it can communicate directly via the GPIO, allowing the HAT to stack directly on the Pi. You can also connect the HAT to a PC as a biometric security device.

Other features include 3x LEDs, a reset button, and an 0.91-inch OLED display for displaying messages like “Access Granted.” The HAT is touted for its robust coating material, 15kV ESD protection, low power consumption, and wide temperature range.

The PiFinger does indeed appear to be the first fingerprint scanner HAT. Seeed offers a Grove — Fingerprint Sensor Module optical scanner designed to be used with the Pi or Arduino. There is also a RaspiReader open source project for building a Pi-connected fingerprint sensor. RaspiReader offers optical scanning via dual Raspberry Pi camera modules. You can also find tutorials on how to connect off-the-shelf biometric fingerprint sensors to a Pi via a UART-to-USB converter

The capacitive technology used by the PiFinger and most smartphones is more difficult to fool than an optical sensor, which is used in most off-the-shelf fingerprint scanner add-ons for the PC. Capacitive scanners also tend to be faster and more compact. Newer fingerprint biometrics technologies include the ultrasonic sensors used on Samsung’s Galaxy S20 phones. For a comparison between fingerprint scanning technologies, see this Dec. 2019 Konsyse story.

Further information

The PiFinger is available on Kickstarter through Dec. 24 starting at 45 UK Pounds ($60), with shipments due in February. More information may be found on the PiFinger Kickstarter page. The product may eventually end up on SB Components’ Raspberry Pi HAT shopping page.


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2 responses to “World’s first fingerprint sensor HAT uses capacitive scanning”

  1. Kamaluddin says:

    Wow that’s great.

  2. rooterkyberian says:

    I wonder whats the point of the HAT form factor (and ability to work directly through GPIO) if it can work as USB device?
    For fingerpint reader it also would be nice to be able to put it anywhere you wanted (thanks to longer cable) as it has to be on to of the device enclosure.

    Seems to me like its a waste of $ – development of alternative communication ways, larger, wasteful form factor, etc. Oh, and the fact alone that you sell less of them means that price cannot be reduced as much as with a generic USB device.

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