Institute of

Cognitive Integrated Sensor Systems

Prof. Dr.-Ing. Andreas König







Student Theses




A Wireless Color-Sensor Module for Sensor Networks in Ambient Intelligence Applications

Close to human perception and stable color sensing is an ubiquitous problem found in numerous disciplinces, e.g., in machine vision for classification and recognition or in general intelligent systems, for instance for intelligent illumination systems in home or working environments.In particular for systems and applications of Ambient Intelligence small, flexible, and preferably wireless modules and networks of such sensor modules are required. In this project, a wireless color sensor was developed based on MAZeT color sensors (MCS3AT, MCS3BT, MCSi) and MICA dot modules. An additional dot extension board and appropriate software was designed and implemented. The system was validated for typical color classification tasks, e.g., for medical laboratory object recognition. Future work will consider  the use of multiple wireless color-sensor modules as a component for intelligent illumination systems, both for machine vision as well as for home applications.


The information conveyed by color is of significant interest in numerous application fields, ranging from machine vision applications for quality assurance as well  as object segmentation, classification and general recognition tasks of intelligent engineering systems. For instance, the classification of medical objects displayed below, which has been pursued in a separate project activity, shows clearly the issue and benefit of color for the recognition process. 

For corresponding sensing activities, in particular, the stability or color constancy of the sensing element and module is decisive for the overall system performance. A common problem in machine vision is the aging of the applied light sources, which lead to a gradual degradation of system performance. A similar problem can arise for color sensors with insufficient long-term stability of their transfer characteristics. In addition, the application in distributed embedded systems and applications, e.g., for Ambient Intelligence, imposes further restrictions on the physical size and communication of an aspired sensor modul. Minimum size as well as wireless communication would be desirable features for a color-sensor module applicable to the above outlined fields and needs.
As a system with such characteristics was not available, a project was started to design such a module, incorporating appropriate stable color sensor elements on a embedded platform suitable for Ambient Intelligence as well as other applications. With regard to their unique properties sensors from MAZeT where selected for the project (MCS3AT, MCS3BT, MCSi; As embedded system platform   the MICA system and MICA dot modules ( where selected, which were also the common platform in a local Ambient Intelligence priority programme in the context of which our color-sensor module project was initiated. An extension board with a MAZet transimpedance amplifier for the three color channels was designed for the MICA dot system.



The output voltage range for the photo current range of these amplifiers, whiche are fed to the local ADC of the MICA-,module in a sequential fashion, is flexibly be determined by programming. More details can be found in the publication enlisted below. The following schematic describes the color-sensor board circuit.


This extension board was attached to a standard MICA dot mote. Software was developed by the system designer both for the mote as well as for the base station, that serves to communicate with the PC (TinyOS and Linux/Cygwin). The software was enhanced for the principle polling and reading of multiple distributed color-sensor modules.


A basic validation of the hardware setup and the developed software was carried out employing an LED-based light source with temporally changing color composition:

After basic validation of the system's operability, it was applied to a more realistic task of color classification. Two series of 100 repeated measurements for each color (class), were made with the MCS3BT, based on a calibration paper stripe displayed below, and used in NN-classification (QuickCog). For this simple problem, a classification rate of 100% could be achieved.

In the next steps of the work, the system was applied to a more practical problem abstracted from another R&D-project in the field of medical laboratory automation (This project will be reported in detail on a separate page). Medical probe tubes have to be distinguished prior to handling and automated decapping by a laboratory robot system. Part of this recognition process is used as another benchmark for the color classification system based on the wireless color-sensor module. The following simple setup was employed for the color classification investigations:

A collection of seven tube types and an eight uncapped tube were the basis for generating a training and a test set with 100 recordings each and overall eight classes to be distinguished by the colr classification system. Again, data was registered by the previously illustrated setup and transferred to the QuickCog system for NN-classifier training, resubstitution, and generalization.

 A recognition rate of 99.875% (type 6 to type 2 confusion) was achieved in generalization, wheras resubstitution was free of errors. By these investigations the color classification system and the wireless color-sensor module was successfully validated. In ensuing work, recent true-color sensors of MAZeT were employed to achieve more capable color-sensor modules. Further, several modules were implemented to allow the spatial registration of lighting conditions, e.g., in home or working environments, such as briefly sketched in the following figure from a feasibility study conducted with two partner institutions in 2003 in the context of Ambient Intelligence activities:

The color-sensor module will serve in teaching as a vehicle of applying an analog neural network chip (SILIMANN; for color classification in the Neurocomputing course of the institute. Professional color sensing systems for industrial purposes meanwhile have become commercially available. The color-sensor module is also considered as a research vehicle for our work on reconfigurable analog and mixed-signal electronics, e.g., replacing the transimpedance amplifier by a reconfigurable field.


  Status:   concluded, duration 08/2003-12/2005
  Financing:   Local Priority Programme Ambient Intelligence in 2003,  Self-Financed in 2004 and 2005
  Contact:   Prof. Dr.-Ing. Andreas König
  Contributors:   Thomas Gräf (Student assistant, HIWI)
      T. Gräf and A. König. A Prototype of a Wireles Color Sensor Module for Automated Quality Inspection, Object Recognition and Color Sensor Networks for Intelligent Illumination Systems. In Proc. of  Int. Conf. on Instrumentation, Communications and Information Technology ICICI 05, Institute Teknologi Bandung, Bandung, Indonesia,  August 3-5, pp. 780-785, 2005.