Transcript of Detection of Harmful Algal Blooms Matthew Barboza, Supervising Professor Dr. Sungyong Jung Summer...
- Slide 1
- Detection of Harmful Algal Blooms Matthew Barboza, Supervising
Professor Dr. Sungyong Jung Summer REU National Science Foundation
AMIC PHOTODIODE For generic p-n diode: Diffusion current = Drift
Current Reverse biasing a diode reduces diffusion current,
resulting in a net reverse current For photodiode: Window allows
photons into material, a percentage of photons create electron-hole
pairs (EHPs) Negligible increase in Diffusion current, dramatic
increase in drift current Effectiveness of photodiode -
Responsitivity: the ratio of reverse current to power of incident
light. Expressed in amps/watt The FDS1010 has a speculated
responsitivity of.5 A/W for 780 nm wavelength light. Summary and
Conclusion The result from the ADC gave an accurate representation
of the input voltage. Any discrepancy can be attributed to the
potentiometer. The photodiode showed both a noticeable increase in
current with an increase in light and a stable output regardless of
a varying bias voltage. Further testing will include a reliable
control of light with the laser diode and the use of the
transimpedance amplifier to allow the microcontrollers ADC to
indirectly measure the response from the photodiode. Materials o A
dsPIC33FJ128MC802 microcontroller from Microchip. o The
microcontroller will be programed using C code and the manufacturer
provided development environment, MPLAB X, and a separately
purchased ICD 3 o D7805I laser diode: 5 mW optical power output
with 780 nm wavelength o OPA380 transimpedance amplifier from
DigiKey o FDS1010 photodiode from Thor Labs o Agilent E3620A Dual
Power Supply, Agilent 34401A Digital Multimeter, DSO-X 2004A
Oscilloscope Abstract The purpose of this project is to create a
remote sensor array that will detect the presence of toxins in
large bodies of water released during harmful algal blooms. The
proposed solution will consist of a sensor that will: i) provide
pulses of light through an optical antenna array; ii) diminish the
intensity of light as the toxin concentration increases; iii)
provide a signal that corresponds to the presence of toxins. My
role in the project is to develop a prototype circuit that will be
used as a proof of concept. Testing has been done to ensure the
selected components are working as expected. Acknowledgements Thank
you to Dr. Sungyong Jung and Mohammadreza Moghadam for their
patience, guidance, and support, and to the National Science
Foundation for their financial contribution: grant #EEC-1156801.
Introduction A hazardous algal bloom occurs when a sudden increase
of nutrients in large bodies of water leads to a rapid growth of
first-order organisms that can cause harm to their environment,
e.g. the release of the toxin microcystin. Our plan is to create a
remote sensing node that will monitor for the presence of specific
toxins and wirelessly transmit any detection to a central location.
This will be done by providing a pulse of light directed through a
film that reduces its intensity when the target toxins are present.
The reduction of light will be measured by a photosensor to provide
a signal that will correlate to the concentration of toxin..
PHOTODIODE RESPONSE The photodiode was placed in series with a
measured resistance and a voltage source. As the voltage source
increased, the diodes reverse bias voltage was measured and the
reverse current was calculated from the voltage across the
resistor. Several data points were collected to obtain a
current-voltage relationship. The process was repeated under a
fluorescent lamp to see the effect of increased lighting. ADC
PERFORMANCE The microcontroller is programed to convert a voltage
signal in the range of 0 to 3.2 V into a 10-bit number. The signal
was created from a potentiometer, which has its bulk resistance
located between the voltage supply and ground. The upper four bits
of the result are used to drive four output pins of the controller
connected to leds. This allows me to see what the ADC is measuring
in.2 volt increments. By sweeping the wiper across its full range
and measuring at what input voltages the output leds change their
value, I can get an accurate representation of how close the ADC
result is to the applied voltage.. a) Array of sensor nodes
transmitting data to central location b) Proposed integrated
circuit for microcystin detection a) b) Materials Circuit close-up
a) ADC test set-up b) ADC test schematic c) ADC test results b) a)
c) a) Photodiode test set-up b) Photodiode test schematic c)
Photodiode test results b) a) c)