PIC32-Powered NIR Spectroscopic "Banana Scan" Can Tell You Whether Your Lunchtime Fruit Is Ripe

Based on detecting the levels of chlorophyll-a in a near-infrared spectrographic scan, the low-cost Banana Scan proves accurate — if slow.

Gareth Halfacree
a month agoSensors

Cornell students Christina Chang, Michelle Feng, and Russell Silva have written up a project to build a PIC32-based device for determining fruit ripeness via spectroscopic analysis: the Banana Scan.

"Sometimes it is difficult to judge the ripeness of fruit, or we simply forget about our fruit until they’re rotten," the three students write of their project. "By using spectroscopy to monitor the change of chlorophyll-a levels in fruit, the device we built can track the ripeness of a variety of fruit, including bananas and oranges."

"The system consists of a spectral sensor that measures the intensity of light waves at various wavelengths. The sensor is mounted on an XY plotter, which moves the sensor underneath a clear piece of acrylic sheet. The fruit sitting on top of the sheet are scanned, and the readings from the sensor are mapped to a color map on a TFT screen connected to a Microchip Technology PIC32 microcontroller (MCU)."

Built around a salvaged XY plotter linked to an Adafruit Stepper Motor HAT connected to a Raspberry Pi running a Python program, the PIC32-based scanner uses a low-cost SparkFun near-infrared (NIR) spectral sensor breakout board. The fruit to be tested is placed underneath an acrylic panel and scanned at a set distance, and the reflected infrared light analyzed to ascertain the fruit's concentration of chlorophyll-a — and displaying the levels as a 12x12 colour map covering 12cm² of the target fruit.

"The user could differentiate areas with unripe bananas and oranges from those with ripe bananas and oranges," the trio found. "Also, the system sacrificed speed for accuracy: scans of the entire 25.40cm × 30.48cm scanning area took around 15 minutes to complete."

Full details are available in the January 2021 issue of Circuit Cellar or on the Circuit Cellar website.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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