This is an easy to construct precision electronic event logger and using this we may be able to measure time differences in two events in range between 0.02 seconds to 6.8 seconds.
This system is mainly design around PIC16F73 microcontroller and 4040 binary ripple counters. The main counter clock (reference counter) is oscillated around 2MHz. Most of the counter related components of this system are based on CMOS family of ICs. If you need more precious lower limit it is recommended to replace all these CMOS family of ICs with TTL equivalents (e.g: 4027 by 74HS73 with slight changes and 4040 by 74HC4040). The clock frequency of the existing counter can also increase up to 6.0MHz.
The counter gets activate and deactivate in positive edge of the input signal. Thanks to the wider operating voltage of the CMOS ICs this counter may be able to handle +5V to +15V of input signal. At the end of the counter session system release total tick count to the RS232 interface and it can receive through any serial terminal software. When applying the inputs it is recommended to maintain minimum of 100ms of interval between each session.
This event logger is useful for physics and electronic experiments, sports events, assembly line monitoring, etc. The input mechanism (e.g: sensor type, logic leveling, etc.) of this system is depends on its application.
The theoretical limit of input interval of this system is wider than above specified values, but we test our prototype in above range and values generated through out-of-range inputs are not guaranteed.
This system is release as an open source hardware project and license under the terms of Creative Commons Attribution 3.0 Unported License. All the project source files, compiled binaries and schematics are available to download at elect.wikispaces.com.