Published January 31, 2023 © CC BY

Arduino speedlog for small crafts

Design, construction and programming of a simple speedlog for use in small crafts

BeginnerFull instructions provided2 hours51

Things used in this project

Hardware components

Arduino UNO

PCF-8574 I2C to parallel converter

KY-003 Hall effect switch

LCD 1602 16x2

Story

MECHANICS

We start by building the impeller and the frame, using my own design available in Thingiverse:

https://www.thingiverse.com/thing:4279708

You will find STL files for the four parts:

1 x top frame, para la electrónica
2 x Bottom frame, para sujetar el rodete
1 x Impeller

You will also need the following mechanical parts:

4 x Small circular magnets (5 mm diameter, 0.1 mm thickness)
1 x M3 screw 15 mm
1 x M3 self locking nut
2 x M3 washers

I have printed the parts in PLA (white and orange, use your preferred colors) with a Da Vinci Jr. printer. I have used cyanoacrylate adhesive for glueing the different parts. Print the impeller and make a 3mm drill for the axle. Then glue the four magnets in place, tangentially in the tips of the impeller. Then glue the two washers around the drill. Their intended mission is avoid plastic-plastic friction when the impeller turns inside the frame. You can find the finished impeller in the image below.

Then print the three parts of the frame and then glue them in place, observing a correct alignment. Then insert the impeller, and make it firm with screw and nut. take care of not applying excessive torque, otherwise the impeller will not turn correctly. In my case, the screws can freely rotate in the frame. You can find the final speedlog below.

ELECTRONICS

The operation of the device is very simple. The ingressing water flow makes the impeller turn. Because the magnets are located on the tips of the impeller, we can know when a blade passes by theta part of the frame, because the is a variation of the magnetic field, which is measured using a Hall effect sensor. In this way we can measure the rotation speed of the impeller (each full turn corresponds to detecting the four magnets sequentially). The rotation speed of the impeller will be proportional to the actual speed over water of the craft (this is NOT really in this way, but for the intended use the difference is negligible ).

The electronics are quite straightforward. The KY-003 can be powered either with 5V or 3.3V. This outputs a high state signal if it detects the magnetic field, otherwise it stays at a low state. The LCD 1602 presents 16 columns and 2 rows, and it is interfaced with a parallel bus. In order to simplify its use, we use the PCF-8574 to convert from I2C to a 8-bit parable port and viceversa. Both the LCD and the module are powered with 5V.

PROGRAMMING

The code is almost trivial. In the loop () function the Hall switch is polled, so that we can maintain a counter of the 0-1 and 1-0 transitions (no magnet->magnet and magnet->no magnet). Every 250 ms the actual count is shown in the LCD and it is simultaneously dumped to the serial port (you can plot the counter values with the Arduino IDE). And that's all folks!!

Depending on the intended use of the speedlog, the counter might not be sufficient. If we want to know the actual speed over water, this can be estimated proportionally to the impeller count as follows:

speed_over_water = K * counter

We can find the desired K constant in multiple ways. One of the most used if to place the speedlog in a GPS enabled sailing craft. The craft is sailed at constant speed over a short course, for instance during a minute. For this to work, the sea state must be calmed, otherwise the measurement will not be accurate enough. The value of the K constant can then be estimated as follows:

K = gps_speed / counter

(DISCLAIMER: the GPS measures the speed over ground, while the speedlog measures the speed over water, which might be different in presence of water currents. A calmed water might assure that both speed are similar)

WORKING

For making the speelog to work we only need to turn the impeller, either by hand (practical for preliminary test) or by using a water current (initially in a bathtub or directly from the water tap). It is simpler to make the initial tests at home instead of trying at see to only know something is not working properly. You can watch the system working in the following video:

Schematics

Code

Arduino source code

/*
 * Copyright (C) 2020 Humberto Martínez Barberá
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses></http:>.
 */

// Paddlewheel speed log for the Arduino UNO
//

#include <LiquidCrystal_PCF8574.h>
#include <Wire.h>

/*-------------------------------------------
    Connection pins
 --------------------------------------------*/

#define PIN_AX A0       // Hall effect sensor analog intput
#define PIN_LED 13      // LED debugging output

/*-------------------------------------------
   LCD
 --------------------------------------------*/

LiquidCrystal_PCF8574 lcd(0x27); // set the LCD address to 0x27 for a 16 chars and 2 line display

/*-------------------------------------------
    Timers
 --------------------------------------------*/
#define TIMER_SER 250

uint32_t timerSER;

/*-------------------------------------------
    Variables
 --------------------------------------------*/
bool has_lcd = false;
bool state = false;
int count;

void setup () 
{            
  // Set IO pin configuration    
  pinMode (PIN_LED, OUTPUT); 
  pinMode (PIN_AX, INPUT);

  // Open serial port
  Serial.begin (115200);

  // Initialise LCD and check for erros
  Wire.begin();
  Wire.beginTransmission (0x27);
  int error = Wire.endTransmission ();
  if (error == 0)
  {
    Serial.println ("LCD initialised");
    has_lcd = true;
    
    lcd.setBacklight (255);
    lcd.home ();
    lcd.setCursor (0, 0);
    lcd.print("Ardu Speed Log");
    lcd.setCursor (0, 1);
    lcd.print ("Count: ");
  }
  else
  {
    Serial.print ("LCD error=");
    Serial.println (error);
    
    has_lcd = false;
  }

  // Initialise counters
  timerSER = millis (); 
  count = 0;
}

void loop () 
{
  int       hall;
  bool      level;
  uint32_t  curtime, dt_time;

  // read current timestamp
  curtime = millis();

  // read hall effect sensor
  hall = analogRead (PIN_AX);
  if (hall > 512)
  {
    level = true;
    digitalWrite (PIN_LED, HIGH);
  }
  else
  {
    level = false;
    digitalWrite (PIN_LED, LOW);
  }

  // check if there is a state change
  if (level != state)
  {
    count ++;
    state = level;
  }
  
  dt_time = curtime - timerSER;
  if (dt_time > TIMER_SER) 
  {
    Serial.println (count);

    // display counter on LCD
    if (has_lcd)
    {
      lcd.setCursor (7, 1);
      lcd.print (count);
      lcd.print ("   ");   
    }
    
    count = 0;
    timerSER = curtime;
  }
}

Credits

Humberto Martínez Barberá

7 projects • 3 followers

B.Sc & M.Eng Computer Engineering PhD Computer Engineering B.Sc & M.Eng Naval Engineering Associate Professor (University of Murcia, Spain)

Contact

Comments

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Arduino speedlog for small crafts

Things used in this project

Hardware components

Story

MECHANICS

ELECTRONICS

PROGRAMMING

WORKING

Custom parts and enclosures

Thingiverse CAD files

Schematics

Fritzing circuit schematics

Code

Arduino source code

GitHub repository

Credits

Humberto Martínez Barberá

Comments

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Arduino speedlog for small crafts

Arduino speedlog for small crafts

Things used in this project

Hardware components

Story

MECHANICS

ELECTRONICS

PROGRAMMING

WORKING

Custom parts and enclosures

Thingiverse CAD files

Schematics

Fritzing circuit schematics

Code

Arduino source code

GitHub repository

Credits

Humberto Martínez Barberá

Comments

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