Project 007 – Solving interfacing problem

USB Fiber-optic interface

This client was an electronics manufacturer that needed to do certification EMC tests on a series of new RF-sensitive products (PIR passive infrared motion detectors). He wanted not only that his products would pass the tests, but he also wanted to see what the impact of electromagnetic environments, such as that of the EMC immunity test, would be on the behavior of the devices. Since routing copper cables from the device to outside of the test chamber would have affected the tests, as would a nearby datalogger, another solution needed to be found.

The solution was to use a fiber-optic interface on the test models. The device-under-test was fitted with a minimum amount of extra electronics and an optic transmitter, which could easily be omitted from the production model. Only a small change in the embedded software was needed to output a digital data signal.

These USB fiber-optic interfaces were designed and built for use on the computer side, where the optic signal from the device could be received. The USB interface was based on a Microchip PIC18F14K50 microcontroller with firmware written in assembly language. The device signals could now easily be viewed and logged using the Windows PC-software application that was also written for this project. The PC-software was written in Delphi Object Pascal.

After analysis, the motion detectors could be improved since it now became clear which parts of the electronics circuits were most sensitive to external radiation.