Synthesis of signal formation and processing blocks of diffuse light reflection sensor using FPGA PSoC5 microcontroller

Abstract

The problem of partial implementing the functionality of the electronic blocks for forming and processing the diffuse light reflection sensor's signal using an FPGA-microcontroller PSoC5 is solved. The topicality of this problem is caused by necessity of precision and high resolution measurement of the difference between, on the one hand, the reference signal of light reflection from the clear sensor's working surface and, on the other hand, the signal of diffuse light reflection from the inspected corroded surface. For this purpose, in particular, a channels' multiplexer, measuring and reference operational amplifiers of the second stage, a delta-sigma ADC with differential inputs, as well as a PWM control and synchronization scheme are implemented on the built into microcontroller FPGA consisting of universal digital blocks (UDB) together with programmed logical devices (PLD). The only components implemented outside the FPGA-microcontroller are the first stage operational amplifiers (in amount of sixteen), the current pulses generator for LED, as well as power supply block. The combination of components synthesized on FPGA with a powerful 32-bit Arm Cortex-M3 core makes it possible to ensure flexibility of settings, to minimize the influence of dark currents of sensitive elements of the sensor's photodiode linear array as well as noises, to align programmatically the sensitivity of the measuring channels and to carry out sensor calibration. Thus, noise mitigation is implemented programmatically by ADC's data collection and averaging in measurement buffer or calibration buffer (for reference signal from clear working surface). Several software routines for mode selection and settings, channels scanning (including measurement and calibration with alignment), as well as for measurement data (difference between the measurement and calibration buffers) displaying and transfer to PC (via one of onboard communication devices) have been developed. These all features can allow implementing the algorithms for deep analysis of measurement data and for calculation of the characteristics of surface corrosion defects.