ph d scientist infrared sensor

Posted on Feb 6, 2014

Build a device to determine the depth of the flocculent layer in a lake. The flocculent layer is a mud layer that has a similar consistency of water. It is pretty difficult to determine its depth accurately from the surface. I have a paper that describes a device able to measure it precisely from the surface and I think that I can build it, but there aren`t any part numbers. I need to order the right

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combination of parts. The idea is to use an infrared LED, which is placed 2-cm away from a IR photo transistor which is high when the light is blocked. The flocculent layer is sufficient to cut the beam. Once the beam is cut, the transistor is low and is connected to a 741 op-amp configured as a voltage detector, which triggers a buzzer (when the set point of the transistor is passed). The reason infra red is used instead of a regular full light LED is that infrared is attenuated by water and thus, surface light does not interfere with the readings (at the floc layer depth, there is no ambient IR light). A 2-cm layer water does not cut the beam. A 2-cm layer of flocculent layer however cuts the beam of the IR LED. From the paper: "The infrared diode light source has a constant current supply (about 10 mA) determined by Rd. The amplifier is a common 741 op-amp, available at any electronics parts store. Pin numbers for the op-amp are shown on the schematic;pins 1 and 5 are not used. The circuit board used in the assembly is a small perf-board, also available at any electronics parts store. The entire circuit operates on a 9-volt alkaline, transistor battery which should provide at least 24 h of continuous service. The buzzer you have selected requires an oscillator to drive it. You want a buzzer such as the SMB-12L Star 12VDC Buzzer from Goldmine, which operates from a DC voltage You have selected a photodarlington...

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