Introduction

This is a follow-up to the previous post, “A Simple Pump Test”. There were several complications with storing the pump data on an SD so this post will describe a new method that stores data on the Arduino’s own memory.

Background

In the field, the pumps will be run for 2.5 minutes per sample for 24 samples, resulting in one hour of total runtime. As described in the previous post, the pumps used in the sampler are poorly documented and information on their lifespan and behavior under long periods of use is needed. 

The SD breakout board used in the previous test was a 3.3v board and was not compatible with 5v arduino logic without some voltage conversion in between. While it worked some of the time, it resulted in corrupt data after a few points. Rather than using a 5v board or something to step down the signal voltage, the Arduino’s own memory can be used to store a small amount of data.

Arduinos have a small amount of available memory that doesn’t get reset between power cycles, known as EEPROM. A single byte can be stored per register, and an Arduino Uno has 512 available registers.

Setup and Method

A 12v peristaltic dosing pump is wired such that the positive end is connected to a 12v source and the negative end is split between a .85 Ohm resistor and the Arduino’s A0 analog input pin. The Arduino’s GND is connected to GND on the power source and VIN is connected to 12v. The other end of the .85 Ohm resistor is connected to GND.

A jumper wire connects GND to the Arduino’s digital pin 3, which is initialized to INPUT_PULLUP.

When powered on, the Arduino continuously checks that pin 3 is LOW. If it is, the voltage across the .85 ohm resistor is effectively measured via an analog read of pin A0 and the value is stored in a register of EEPROM. The register address is incremented and the loop resets.

If pin 3 is HIGH, data collection is turned off and the Arduino checks for a serial input of “p”. If the user inputs in the serial monitor “p” then it prints all the data from the registers separated by spaces. This data should be copied and pasted into a text file, but can be reprinted as long as pin 3 is HIGH.

Code

// A simple voltage logger that is 

#include <EEPROM.h>

const int sensorPin = A0;
const int startPin = 3;

long sTime = 0; // last sample time
int maxPoints = 240; // maximum number of points to store
int sDelay = 30000; // delay between samples
int addr = 0;

void storeData();

void setup() {
  pinMode(startPin,INPUT_PULLUP); // if grounded, enable recording
  pinMode(sensorPin,INPUT);
  Serial.begin(9600);
  Serial.println(“Initializing…”);

  
  analogRead(sensorPin);
  delay(1000);
  analogRead(sensorPin);
  delay(1000);
  analogRead(sensorPin);
  delay(1000);
  analogRead(sensorPin);
  delay(1000);
  
  Serial.println(“Initialized.”);
}

void loop() {
  
  //If datalogging is enabled, store data in a new address
  if(!digitalRead(startPin)){
    if(millis() – sTime > sDelay){
      Serial.println(“reading data point ” + String(addr));
      storeData();
    }
  }
  else{
    Serial.println(“Enter ‘p’ to print out data”);
    
    while(digitalRead(startPin)){
      int input = 0;
      
      if(Serial.available() > 0){
        input = Serial.read();
      }
      
      if (input == 112){
        for(int i = 0; i < maxPoints && i < EEPROM.length(); i++){
          Serial.print(EEPROM.read(i));
          Serial.print(” “);
        }
        
        Serial.println();
      }
    }
  }
}

/*
 * store the sensorPin voltage and increment the address. If the address has
 * reached the limit of number of the points or hit the last address of
 * the EEPROM, don’t store data and return from the function.
 */
void storeData(){
  if(addr == EEPROM.length() || addr == maxPoints){
    Serial.println(“Max addr reached”);
    sTime = millis();
    return;
  }
  EEPROM.write(addr, analogRead(sensorPin)/4);
  sTime = millis();
  addr++;
}
 

Python Code

# This code will take in data via a text file that was collected using
# the pumptest arduino code. Data points should be separated by spaces.

import matplotlib.pyplot as plt

data = []
splitter = []
voltage = []
current = []
average = []
avg = 0

with open(‘pumplog_2_p1t2.txt’) as f: #file name for test data to be graphed
    reader = f.readlines() #read in the data

for line in reader: #split up the data. Could be conbined with converting to int but is more readable this way.
    splitter.append(line.split())

for point in splitter[0]:
    data.append(int(point) * 4) # turn each point of data into an int. Data values were divided by 4
                                # to fit into EEPROM.

for point in data: # calculate the voltage at each point.
    voltage.append(point * 5 / 1024)

for point in voltage: # calculate the current at each point.
    current.append(point / .85)

for point in current: # calculate the average current.
    avg += point
avg = avg / len(data)

for point in data: # turn average into a plottable list
    average.append(avg)

plt.plot(current)
plt.plot(average)
plt.title(“Pump 1 Test 2”) #rename based on test
plt.xlabel(“time (minutes)”)
plt.ylabel(“current (A)”)
plt.show()

Initial Results

Conclusion

Three tests have been run so far. They were graphed using Python 3 and matplotlib.pyplot. Another test is currently being run on the second pump. The data between the two pumps will be compared using a two-sample T test to check if the two pumps perform the same. The same method will be used for the pumps under condition of pumping water.

The initial three tests might suggest that there is a long term decrease in the pumps’ current draw. Future tests should be conducted for a full day and a linear regression analysis should be performed. More importantly, such inconsistency in the current draw suggests the flow rate though these pumps is not constant. A test should be conducted to observe the trend and variance in the mass flow rate of water through the pump via a logging scale. A better conclusion can be made once the first round of testing is finished and statistically analyzed.

Introduction

Peristaltic 12V dosing pumps are cheap and provide a large enough volumetric flow rate for our needs. Unfortunately there is not much information available on the type we are using. This post will discuss the method we are using to test the reliability and consistency of these pumps over a period of two hours. It is the first of several tests we will be conducting on different components of our water sampler.

Setup and Method

A pump is held in a clamp and powered from a 12v source. A .85 ohm, 1.4 watt rated resistor connects the pump to ground. The voltage across the .85 ohm resistor is measured over time using an arduino and this data is stored in an SD card. 

The arduino reads the voltage on an analog pin and stores that, along with the time since starting in milliseconds, in the SD card. Initially there is a delay of one second in between data points and after sixty points the delay increases to one minute. This data will be transferred to a computer where it will be used to show the current through the pump over time.

Code:

// A simple voltage logger that is heavily
// based on the SD Datalogger example sketch.

#include <SPI.h>
#include <SD.h>

const int chipSelect = 4;
const int sensorPin = 0;

int n = 0;

void setup() {
  Serial.begin(9600);
  while(!Serial){
    ;
  }

  Serial.print(“Initializing SD card…”);

  if(!SD.begin(chipSelect)){
    Serial.println(“Card failed, or not present.”);
    return;
  }
  Serial.println(“card initialized.”);

}

void loop() {
    String dataString = makeDataString();
    File dataFile = SD.open(“pumpLog.txt”, FILE_WRITE);
    if(dataFile){
      dataFile.print(dataString);
      dataFile.close();
      Serial.println(dataString);
    }
    else{
      Serial.println(“error opening pumpLog.txt”);
    }

    if(n<60){ 
      delay(1000);
      n++;
    }
    else delay(60000);
    
}

String makeDataString(){
  return String(analogRead(sensorPin)) + “, ” + String(millis()) + “; “;
}
 

Conclusion

Once the pump has run for two hours, the power will be turned off and the data from the SD card will be transferred to a computer. Using Ohm’s Law the voltage across the resistor will show the current through the system. The data will show what kind of trend, if any, the current draw has through the pump. It will also show if the current draw varies with a resolution of one minute.

This test will be repeated for two other pumps. Then it will be repeated with water flowing through the pump tube.