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Sailing Speedometer



Sailing Speedometer, or SailSpeed, is a project that I’ve been working on to provide a speedometer for small sailboats.  The speedometer uses a GPS to capture the speed and then a double side display unit to show the speed.  The display unit is attached to the boom of the sailboat.   The display read outs are shown on both sides so the speed can be seen whether you are on a port or a starboard tack.

The display unit is attached to the boom with rope and a jam cleat.  The display unit is snugged up against the boom so it doesn’t flop around as the boat hits waves or the sail is slammed.

The image below is a quick sketch of where the display unit will reside while the boat is underway.



I have been going through prototypes to select the proper components.

First Prototype

My first prototype used an Arduino Uno and an Ultimate GPS.  These are both rather expense parts, but they were readily available for a quick prototype.  The Arduino was programmed to capture the speed from the GPS and then showed the speed on 6, individual 7-segment LEDs that are 1.2″ in height.  I want a large display surface so the speed is easy to read from anywhere on the boat.

The image below shows the first prototype.  In the image you can see how there are two separate displays, one for port and one for starboard.  The Arduino interfaced with shift registers to feed the data to each of the displays.  The shift registers for each side required 3 pins so this meant I only needed 6 pins from the Arduino to show the speed.  The GPS also required 2 pins and I still had left over pins for an on/off switch, an LED to show power and a momentary switch to switch between knots, kph and mph units.

Granted, this is a rather bulky version with all of the wires running about, but it was the first prototype.


Second Prototype

The second prototype was much smaller.  I switched from an Arduino Uno to an Arduino Pro Mini, a Skylab SKM53 GPS, some circuit boards to reduce the wiring to the shift registers and ribbon cables to clean things up a little.


This version is still too bulky, but it’s going the right direction…smaller.  What I found after doing all of this work is that the LEDs that I selected were not the right product to be seen in full sunlight.  That was a bad day.

Third Prototype

I did some searching and decided on the Lumex LCD-A401C71TR to replace the 7-segment LEDs.  This LCD uses a fluid type called twisted-nematic (TN).  There are 3 primary fluid types used for LCDs which are TN, STN and FSTN.  Each provide different quality and viewing angles.  The TN fluid type is the least expensive and the worst viewing angle, but I’m going to test to see if it is acceptable for this project.  The FSTN is the best, but also the most costly.


I believe I’ll continue with the Arduino Pro Mini for the microprocessor.  It is easy to program and relatively inexpensive.  I’m also going to stay with the SKM53 GPS.  It isn’t too expensive in medium quantities.

I purchased my first boards through OSH Park and I’m happy with the quality so I’ll probably stick with them.  I need a major redesign of the board layout.  The first board layout is shown below.  I called the circuit the “Shift Number Module” because it allowed for 3, 7-segment LEDs to be driveen by 3 pins, plus VCC and GND via shift registers.  I used EAGLE PCB Design Software to design my board and I was able to create an aa


What’s next, prototype version 3 with the new LCD and the new circuit board layout.  The new layout will include a spot for the Arduino Pro Mini and the SKM53 GPS.

Fourth Prototype

I can’t believe I’m up to 4 prototypes.  Prototype 3 failed because of the number of pins I had to solder.  This wasn’t practical.

I started looking for a better option for my display and ran across the New Haven Display NHD-C12864A1Z-FSW-FBW-HTT LCD with is a 126×64 transflective display – which means you can see it in the sunlight.

After some struggles getting the display to work with the Arduino Pro Mini which can be read about on my blog post, I’m finally on the way to using this display.

I think this is the right one.