Thursday, November 26, 2015

ZFM-20 fingerprint capture library

ZFM-20 is optical fingerprint sensor module series developed by Zhiantec. Resolution of this fingerprint modules are 256×288 pixels and depending on the module it can be accessible over UART or USB interfaces. Other than capturing fingerprints this module has inbuilt DSP to process and verify captured fingerprints.

This ZFM-20 fingerprint library is developed to capture and retrieve fingerprint images from the above sensor module. The main purpose of this library is to use ZFM-20 sensor with PC as low cost fingerprint capture unit and because of that, in-module fingerprint processing and verification functions are not implemented in this library.

ZFM-20 fingerprint sensor test setup with CH340G serial to USB converter.

ZFM20-LIB is x86 native shared library and its implemented using Lazarus/FPC. This library is developed to use with most of the programming languages which including C, C++, Delphi, FPC, Microsoft .net framework based languages, etc. Object oriented wrappers for this library are available for both .net framework support languages and for FPC.

This version of ZFM-20 Fingerprint capture library is tested with ZFM-20 series serial fingerprint module with CH340G USB to serial converter. Generally this library is design to work with any USB to serial converter which including FT232, CP2101, etc. 

ZFM-20 fingerprint capture library is an open source shared library project and it's source code and compiled binaries are available at This library is released under the terms of MIT License.

Monday, November 9, 2015

Dynamic microphone preamplifier

This is single chip dynamic microphone preamplifier which is design to drive using commonly available 12V single rail power supplies. Preamplifier in this article is build around popular NE5532 dual low noise operational amplifier IC and this preamplifier is specifically constructed to drive professional 600Ω dynamic microphones.

Internal view of dynamic microphone preamplifier prototype.

This preamplifier consists with two amplifier stages and initial amplifier is design to get 36dB gain and final preamplifier is used to get 16dB of gain. Preamplifier gain controller is placed in between those two amplifiers and this separation allows reducing clipping in output waveform.

In prototyping stages we test this preamplifier with few 600Ω dynamic microphones with TDA2050 power amplifier. According to our observations this unit produces excellent output with all of these microphones. To get professional results use this preamplifier with 12V battery or with regulated power supply unit and use screened wires for both input and output connections.

Schematic, wiring diagrams and PCB design of this microphone preamplifier are available to download at