Precision colour sensing made easy
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Austrian MicroSemi recently divested itself of its transceiver portfolio, leaving standards such as AS-I stranded. Sensors were selected as the new main field of business, leading to the introduction of a few extremely interesting products such as the JENCOLOR colour sensor ICs.
In principle, the sensor is laid out according to the schemes shown in the two figures accompanying the screen. The main priority is that the part contains but three photo-diodes, all three of which are conveniently located behind a filter to eliminate unwanted spectral components.
The three diodes are located in seperate areas of the main die…
…AMS provides a relatively complex set of signal conditioning circuits
To clarify a few aspects: first of all, the AS73211 is strictly an one-pixel color detector – it has nothing to do with the traditional linear or two-dimensional CCD chips which are well-known from digital cameras. Secondarily, the chip’s intended usage is processes – think about quality control, sorting of goods and similar tasks where accurate color sampling is required.
Finally, the AS73211 is intended to reach extreme high accuracies – its internal DACs can work at 24bit if required.
When compared to a homebrew solution, benefits pop up. ADC linearity and temperature issues are handled by AMS – the chip contains various bits of logic which ensure that issues affecting resolution adversely are handled effectively.
Getting data out of the part is accomplished via an insutry standard I2C connection. In the first step, both CREG1:GAIN and CREG1:TIME must be programmed to set up ADC gain and the time spent on the individual conversion cycles. In the next step, the remaining hardware must be configured – when done, actual measuring processes can be triggered. More information on this is readily available in the excellent datasheet, which is waiting for you here.
On development kits
Like most other optical systems, the AS73211 also puts demands on the accompanying optics. Developers working on sensor software are well-advised to start out by buying the (somewhat pricey) AS73211-AB5 SET DK development kit rather than the basic PCB version – the former comes with a complete optical assembly, thereby taking one bit of hassle off your neck.
… Be careful when selecting your development kit – not all are created equal