Underwater Wireless Communication

[NPB777]

Hello all,

I am right now doing my final year project. We have decided to work on Underwater Wireless Sensor Communication. In this project, we deploy a wireless sensor node inside the water. It has to communicate with that of the buoy like thing (a trans receiver) placed at surface of the water. The trans receiver then communicates with that of Laptop. We want to use 2.4 GHz band for this communication.

Our idea

We have planned to use an Arduino board connected to a pH sensor and a temperature along. The board will be interfaced with a WiFi transmitter. The data collected by the sensors must be transmitted yo buoy floating on the surface. We will enclose this inside a water proof case and immerse that inside the water 15 to 20 cm deep. We will place a WiFi receiver at the surface of the water. This receiver will receive the signals from underwater and re-transmit it to Laptop.

Now here are my following question:

1. What is the best way to implement this project?
2. Can we enclose Arduino kit and WiFi transmitter in a water proof box and leave it into water? Will WiFi work under the water for short distances?
3. Are there any kits readily avaiable to implement this?
4. If not, please suggest me which of the Arduino kits are best for the purpose and other components to be bought.


With regards,
NPB

 

[Externet]

From the buoy to the laptop, the Wifi should have no problems.
From the submerged sensor to the buoy, Wifi will not work, and if it does, will be because of a very short propagation path but not a reliable way to do it.

I would use modulated LED light emission from the sensor to send the data to the buoy for such shallow depths if a direct wire connection is discarded by whatever reason you may have.

Audio or ultrasonic audio is the typical way to do it underwater for deeper or longer paths.

Buying kits is not the best way to learn on a final year.

 

[NPB777]

Will not WiFi work for distance of 10 feet?

 

[Externet]

10 feet underwater, no.

 

[NPB777]

Okay, at least for 20 to 30 cms? Will we get the result?

 

[NPB777]

Can you suggest me a good Arduino processor with WiFi transmitter and receiver? I must be able to interface a temperature of pH sensor with this. The data from these sensors must be transmitted over WiFi for another receiver. Give some suggestions with respect to this.

 

[AnalogKid]

For the pH and temperature sensors, what is the data format (number of bits or bytes per reading), and what is the amount of data per second or per minute you want to communicate? WiFi is overkill for most sensor data, and the very high frequency makes it difficult to use around water.

ak

 

[hevans1944]

Okay, at least for 20 to 30 cms? Will we get the result?

What part of "will not work underwater" do you not understand? The buoy is above water and presumably tethered to the bottom under whatever water it is in, so it won't just float away. Take advantage of this.

Tie your transducer box to the buoy cable with plastic tie-wraps, run a jacketed, shielded, water-proof cable 20 or 30 cm to the transmitter on the surface. Pick a cable (by trial and error if necessary) that will support the submerged weight of your sensor package just in case it become detached from the buoy anchor cable. You can attach the transmitter to the buoy above the surface of the water, mounted inside its own water-proof container. Make sure the volume of the transmitter container is large enough to displace a weight of water greater than the weight of the transducer package without submerging the antenna, just in case the transducer package gets separated from the buoy. That way the transmitter and instrumentation will stay together if they are separated from the buoy and you can use direction-finding antennas to locate them... at least until the batteries go dead.

I agree that Wi-Fi seems to be a little overkill for this application. How far away is the laptop that receives the data transmitted from near the buoy?

You should consider using a peer-to-peer Bluetooth data link such as Zigbee with the Arduino. There are Zigbee shields of various transmitter powers available for the Arduino. Put this transmitter package in a waterproof container that floats on the water and connects to a separate, ballasted, water-proof transducer package that is 20 to 30 cm under the water... or whatever depth you desire. Connect the two packages, one floating and the other submerged, with a shielded multi-conductor cable strong enough to support the weight of the submerged instrumentation package. Do not adjust the instrumentation package for neutral buoyancy when submerged. It must have enough negative buoyancy to hang straight down from the transmitter package that is floating on the surface, but not so much negative buoyancy as to submerge the transmitter antenna. Be sure to tie either the transmitter or the instrumentation or both to the buoy, lest your project float away, never to be seen or heard from again after the batteries die.

This project is as much about packaging to ensure water-tight protection and prevention of corrosion as it is about electronics. You can breadboard or prototype the electronics, and make sure it works in the lab, before venturing out on the water where many surprises await you.

Jeez! So many basic questions for a senior year project! Are you not supposed to figure most of this stuff out by doing your own research? We are here to help you, but I at least expect a considerable amount of work from you.

Hop

 

[davenn]

for RF transmission under water, very low frequency is required
preferably below 100kHz

The LORAN system for communications to submarines was/is around 15kHz from memory
The subs would trail out VERY long antenna wires behind them ... reeling them in and out as required

 

[Alec_t]

Okay, at least for 20 to 30 cms? Will we get the result?

Simply try it and see. Put a cell-phone in a watertight box, submerge it, then call it from another phone.
Water salinity may be a major factor here.