Design, Fabrication, and Calibration of an IR-Based Ballistic Chronograph

Abstract

A chronograph is a device that measures the time between two events. This article discusses the design, fabrication, and calibration of a ballistic chronograph designed to measure the time taken by a projectile to travel a fixed distance between two checkpoints, A and B, along a straight line. The infrared transmitter-receiver pairs at A and B and an Arduino microcontroller circuit confirm that the projectile has crossed these checkpoints. The duration of this event is precisely recorded in the microcontroller’s memory. The system was designed to measure speeds up to 3500 m/s for a projectile 50 mm in length. The time uncertainty of the chronograph was found to be $0.71~\mu $ s. Distance between the checkpoints was measured with a CNC-mounted probe with an uncertainty of 0.10 mm. The overall cost of this local chronograph is 4–33 times lower than the commercially available chronographs. The novelty of the device lies in its calibration, which was performed using another Arduino circuit programmed to control the blinking of the IR LEDs. Two IR pulses of specified widths separated by a specified time interval were sent by electronically controlling the IR sources and detected and measured by the IR sensors. This optoelectronic method of calibration eliminated the need for field calibration, simplifying the process.