On-chip peripheral control of ultra-compact spectrometer

Abstract

Spectrometers are found in applications where substances are classified through analysis of relative light reflection, transmission or fluorescence, commonly used in food, medicine and lighting applications.

The Hamamatsu C12880MA offers low cost and high sensitivity in a small robust package. This project successfully employs hardware features of the NXP MK20DX256 microcontroller to interface with the sensor.

The sensor specifies a relatively high clock rate of 0.2 - 5.0MHz for gating spectral (video) output. Video pixels are captured with a synchronised analogue to digital converter (ADC). A start pulse initiates this process while also determining the integration time. Any jitter or relative variation between these timings will reduce the accuracy of the measurement.

Interfacing at even minimum specified clock rate with low-cost microcontrollers, such as those found in popular Arduino based evaluation boards, can prove challenging. Online examples typically operate at only a fraction of the specified rate, often with little or no regard for jitter or relative timing.

Making use of available on-chip peripherals, the MK20DX256 microcontroller generates accurate control signals with very little CPU intervention. The ADC conversion is triggered by these same events which in turn initiate direct memory access (DMA) for acquired data. This is currently operating at stable clock speeds of 0.2Mhz and integration times from 0.27 to 10mS, this range could be expanded with additional programming if required.

As a proof of concept this project is now ready for further development into a prototype and application to related activities within the research group.