Innovative school-level quantitative chemistry experimental technique (II) an affordable, sensitive, stable and user-friendly colorimeter
The paper is a continuation of Part (I) of the article  published in the Special Issue of AJCE, Vol 9 No. 3, 2019. It introduces a home-made colorimeter sensor which when connected to a commercial digital multi-meter (DMM) can act as a conventional colorimeter. Rationale of the sensor design is based on affordability without sacrificing sensitivity, stability and availability. As such, it has the following features: (i) a professional cuvette is used, ensuring reading display reproducibility (Fig. 1), (ii) improved circuit design , (iii) a RGB tri-colour LED is used instead of optical filter for near-monochromatic light source (Fig. 2), (iv) the “DMM Display” technique is adopted in which the sensor output is limited to a full-scale reading of 2000 mV DC with the DMM’s voltage readings acting as transmittance parameter, (v) do away with the concept of absorbance and Beer’s law which are not recommended for most school level chemistry syllabuses. When using the sensor, output voltage readings are treated as quantified transmittance and that a blank sample transmittance is adjusted to have a voltage reading of 100 mV which is regarded as a full-scale reading of 100 with no unit, (vi) portable with no location limitation and (vii) battery operated capable of long period of continuous operation.