Self Positioning Buoy Measures Depth of Lake

This Self positioning buoy is designed and built by [Geir Andersen]. It was originally designed to measure depths in lakes. He calls it Whirligig. Original post from

Self Positioning Buoy Measures Depth of Lake

The Design Goals

  • The buoy is to be lunched from the shoreline and go to a predefined way point using GPS and compass.
  • When it reaches the way point, the motor will be stopped and the buoy will drift within a preset radius of 5,10,20 or 50m from the way point. When exiting this ‘parking zone’ Whirligig will restart its engine and go back to the waypoint.
  • New way-point coordinates can be issued from a PC on land using XBee communication.
  • Whirligig will constantly update the PC with GPS coordinates and other information as long as its within reach and a connection is established.
  • Whirligig can also be driven manually via the control panel (PC) over the XBee communication, returning information on compass course, speed, rudder angle GPS coordinates etc.


Probe and Pulley System

The buoy itself has no purpose if it hasn’t got a mission and here is where the probe and pulley system comes in.

One of the first jobs for Whirligig is having a probe that will be lowered down to 20m below the surface and measuring pressure (to get the exact depth), water temperature, light from the surface and light from the bottom (reflected light).

The aim is to get measurement from a 20m column of water with 1m intervals. So the probe will be oscillating between the surface and the 20m target.

One dive will take about 40minutes. The hope is to have Whirligig positioned and take measurement for at least a week and the probe recording 24/7.

The new design will look something like this


From above you se the fishing rod holding the probe away from the boat and some of its shadow.


Design of the Probe and Pulley system

Our initial plan was to feed power and read serial signal from the probe and storing it within Whirligig. But as the project progressed we decided to make the probe self sufficient with power and add a battery. Then storing the data on EEPROM or SD card, we were free to use a regular fishing line for the pulley system and greatly simplify the design.

The second problem was, ‘how to sense the bottom and topmost position of the probe’? Several ideas was put on the table until we came up with the idea of just using a line that has the maximum traveling length and as the motor spins unwinding the line, it will reach the maximum depth and without changing the motors direction it will start winding itself up again (a simple solution, but brilliant for our use).

In the topmost position we have a stopper on the line and a micro switch mounted on the fishing rod, giving a signal for changing direction on the motor, and the whole sequence starts over again. The picture below showing the stopper and microswitch.

This is the motor and a spool for the line (this is only a test rig)


This will finaly be mounted inside the lid of Whirligig.


The Control System.


The bottom deck is now completely empty and can host additional scientific equipment in the future.


Underneath the black plate, the circuits for the lantern and pulley systems are mounted. On top of that we have a Arduino with an XBee shield, GPS and a digital compass when it arrives.

Below is a screen shot of the control system (with its debug window open). Written in Visual Studio Express VB.

Self Positioning Buoy Measures Depth of Lake

So where is the project at?

The Author said on the website

As we already have Whirligig complete, the boat part of the project is done.
I have an idea about the fishing rod and pulley system and the circuit with at PICAXE are in place. The lantern is working from its own board also using a 08M PICAXE.
The Arduino is reading the GPS and has control of the rudder servos and motor. I’m still waiting for the compass from Sparkfun to hook that up. Most of the Arduino code has been written and what I miss I have elsewhere in other projects.

The PC control system is almost done. I need at tab and how to control the pulley and probe.
After starting this project I have had a look at the FEZ domino and am wondering if I should port everything over to that board. The main advantages are;

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