Getting back to issues involved in developing an open source data logger based on the arduino:
It seems to me that the development of a shield to handle analog signal conditioning is a key step in making the data logger a broadly appicablel tool. The ten bit resolution of the Arduino A/D converter (ADC) is not an issue as long the signal from sensors is relatively linear and varies so that the voltage change covers a large fraction of the 0 to 5 volt scale. However, in many cases, the range of sensor outputs will vary over a much narrower range, and programmable gain amplifiers will be needed to adjust the dynamic range of voltages that are presented to the ADC. (e.g. resolution of the ADC will not be adequate if sensor output voltages range from 0 to 0.5 V). Also, as many sensor's output varies logarithmically or exponentially with respect to the stimulus, an exponential or logarithmic conversion will be needed to prevent loss of resolution at the low end of sensor input. Based on my limited knowledge of OP amps, it seems that a shield to handle this kind of basic signal conditioning might not be too expensive to make. Of course this leaves out some more specialized signal conditioning needs (e.g. cold junction compensation for thermocouples), but if the shield could handle simple variable gain amplification and logarithmic transformation, it would allow the Arduino's 10 bit ADC to serve adequately for many, many data collection situations.
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