#Basic Inline Turbidimeter
##Purpose
The Basic Inline Turbidimeter is designed to measure turbidity in a body of water, automatically, for the lowest possible price.
##Function
How does the device measure a parameter?
This device is a back-scatter nephelometrer. A pair of infrared light-emitting diodes (IR LED) are mounted on either side of a light-to-frequency sensor. Some portion of this emitted light is scattered by suspended sediment as it passes through a sample of water. This scattered light is detected by an IR-sensitive photodiode mounted at a right angle to the center of the IR LED's light beam. The intensity of light detected by the photodiode is referenced to a calibration curve stored in the device's memory to interpolate the corresponding turbidity value, measured in nephelometric turbidity units (NTU).
How does the device record data?
This device contains an SD card slot for storing data.
How does the device display data?
This device is intended for standalone data logging and does not include a display.
What units does the device report in?
Like all AWQUA turbidimeters, this device reports readings in nephelometric turbidity units (NTU).
How does the device communicate data electronically?
This device does not possess data telemetry capabilities, however they may be added for additional cost. See the Communications repo for options.
##Use Case
Where can the device be safely used?
This device can handle temperatures up to 70C, and is intended for field conditions. It is water proof to at least one foot.
##Power
How is the device powered?
This device uses 3.3V DC power, and requires less than 100mA of current, and uses an internal 3.7V lithium polymer battery.
How much power does it use?
In automated testing, this device was capable of taking a measurement every 15 minutes for 29.5 days.
##Standard and Testing
How was the device tested?
This device has so far only been tested in the Open Source Water lab. The testing consisted of:
(1) immersing a prototype device in a water bath which contains a spin plate for bath mixing
(2) adding small doses of a colloidal suspension to the water bath while relaying readings from the prototype via Bluetooth every 10 seconds
(3) on every fourth dose of colloidal suspension, sampling the water bath with a commercial handheld turbidimeter
(4) analyzing the fit between the commercial and prototype open-source turbidimeter
How did it perform?
Test results may be found in the testing subdirectory in the file basic-inline-turbidimeter_analysis.20151021.xlsx. These data will be updated as further testing is conducted.
What performance standards does the device meet?
We have not evaluated this device against existing standards for backscatter turbidimeters yet, nor have we yet developed a new standard.
##Construction
###Bill of Materials
| Quantity | Part Description | Example Price (each) |
|---|---|---|
| 1 | ATMega328P-PU microprocessor | $2.90 |
| 1 | LMT86 temperature sensor | $1.00 |
| 1 | TSL230BRD | $5.03 |
| 1 | LP2985 3.3V Voltage regulator | $1.04 |
| 2 | 10uF aluminum electrolytic capacitors | $0.24 |
| 2 | 22pF ceramic capacitors | $0.03 |
| 5 | 100nF ceramic capacitors | $0.06 |
| 4 | 100 ohm resistors | $0.10 |
| 1 | 220 ohm resistors | $0.10 |
| 1 | 1K ohm resistors 1% tolerance | $0.10 |
| 4 | 10K ohm resistors | $0.10 |
| 1 | IR LED | $0.47 |
| 1 | Momentary contact button | $1.50 |
| 1 | SPST power switch | $1.50 |
| x | Header pins (0.1" spacing) | $1.50 |
| Total Cost: | $xx.xx | |
| ###Circuit Board | ||
| ####Schematic | ||
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| ####Layout | ||
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| ###Assembly | ||
| [forthcoming] | ||
| ##FAQ and Troubleshooting | ||
| ###Online Resources |