Simple Lightometer ----- Simple Photometer

Simple PHOTMETER, SIMPLE Photometer Keywords: photometric circuit diagram Most light emitting diodes, and the function of reverse photodiodes. That is, when an inverse bias is applied to the light-emitting diode, as the optical level is increased. It will produce a small photovoltaic output. Because the housing of the light-emitting diode is colored and transparent, it is especially suitable for this function. This can build a simple circuit to estimate the state of the week ambient light. Light filter valid for some kind of light color can be obtained in different colors. Have typical narrowband. Although the examples described herein do not reach the design accuracy of the laboratory level photodetector and the mutual impedance amplifier, it produces useful results. Using three light emitting diodes, the experiment will indicate which type of device has the best sensitivity, see the drawings. When the ambient light is expanded to these light-emitting diodes, the current is 10 to 100 nA through each of the light-emitting diodes (depending on the added illumination intensity). This current flows through the base of the transistor Q1 and is amplified. The collector current of Q1 flows between the baser R4 and Q2. R4 is used as a gain correction of the first stage. Q2 provides further enlargement. And drive a bridge D1a and D1B diode on the left. Note that R2 / D1 and R3 / D2 constitute a bridge. Q2's collector current provides a weak imbalance in this bridge, and Table M measures this imbalance. R5 is used to adjust the sensitivity of Table M. Setting R4 and R5 to facilitate table M with a suitable deflection. R4 is useful for selecting a static work point. R5 is useful for adjustment sensitivity. Before making the circuit, it should be checked whether these light-emitting diodes are good light-emitting diodes, and a normal digital multimeter is used to check the voltage across the light emitting diode, approximately 200 mV.

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