Battery powered sensor last 1 week

Martin Tellblom

I have made a sensor based an a Easy/Newbie PCB a pro Mini (3,3V 8Mhz with desolderd power LED and Regulator) attached a soil moisture sensor and checking every 2 hrs. The 2 AA batteries last just under a week.

What do I need to do more to get it to last a little bit longer that just under a week?

The sensor is the one here: https://www.mysensors.org/build/moisture

Her is the code I have adapted to check for battery aswell

/*
   The MySensors Arduino library handles the wireless radio link and protocol
   between your home built sensors/actuators and HA controller of choice.
   The sensors forms a self healing radio network with optional repeaters. Each
   repeater and gateway builds a routing tables in EEPROM which keeps track of the
   network topology allowing messages to be routed to nodes.

   Created by Henrik Ekblad <henrik.ekblad@mysensors.org>
   Copyright (C) 2013-2015 Sensnology AB
   Full contributor list: https://github.com/mysensors/Arduino/graphs/contributors

   Documentation: http://www.mysensors.org
   Support Forum: http://forum.mysensors.org

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License
   version 2 as published by the Free Software Foundation.

 *******************************

   DESCRIPTION

   Arduino soil moisture based on gypsum sensor/resistive sensor to avoid electric catalyse in soil
    Required to interface the sensor: 2 * 4.7kOhm + 2 * 1N4148

   Gypsum sensor and calibration:
      DIY: See http://vanderleevineyard.com/1/category/vinduino/1.html
      Built: Davis / Watermark 200SS
          http://www.cooking-hacks.com/watermark-soil-moisture-sensor?_bksrc=item2item&_bkloc=product
          http://www.irrometer.com/pdf/supportmaterial/sensors/voltage-WM-chart.pdf
          cb (centibar) http://www.irrometer.com/basics.html
              0-10 Saturated Soil. Occurs for a day or two after irrigation
              10-20 Soil is adequately wet (except coarse sands which are drying out at this range)
              30-60 Usual range to irrigate or water (except heavy clay soils).
              60-100 Usual range to irrigate heavy clay soils
              100-200 Soil is becoming dangerously dry for maximum production. Proceed with caution.

   Connection:
    D6, D7: alternative powering to avoid sensor degradation
   A0, A1: alternative resistance mesuring

    Based on:
    "Vinduino" portable soil moisture sensor code V3.00
     Date December 31, 2012
     Reinier van der Lee and Theodore Kaskalis
     www.vanderleevineyard.com
   Contributor: epierre
*/

// Copyright (C) 2015, Reinier van der Lee
// www.vanderleevineyard.com

// 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
// 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.

// Enable debug prints to serial monitor
//#define MY_DEBUG

// Enable and select radio type attached
#define MY_RADIO_NRF24
//#define MY_RADIO_RFM69

#define  MY_NODE_ID 30
int BATTERY_SENSE_PIN = A0;

#include <math.h>       // Conversion equation from resistance to %
#include <MySensors.h>

// Setting up format for reading 3 soil sensors
#define NUM_READS 10    // Number of sensor reads for filtering
#define CHILD_ID 0

MyMessage msg(CHILD_ID, V_LEVEL);
unsigned long SLEEP_TIME = 7200000; //  Every 2 hrs //Sleep time between reads (in milliseconds)

long buffer[NUM_READS];
int index;

int oldBatteryPcnt = 0;

/// @brief Structure to be used in percentage and resistance values matrix to be filtered (have to be in pairs)
typedef struct {
  int moisture; //!< Moisture
  long resistance; //!< Resistance
} values;

const long knownResistor = 4700;  // Constant value of known resistor in Ohms

int supplyVoltage;                // Measured supply voltage
int sensorVoltage;                // Measured sensor voltage

values valueOf[NUM_READS];        // Calculated moisture percentages and resistances to be sorted and filtered

int i;                            // Simple index variable

void setup() {

#if defined(__AVR_ATmega2560__)
  analogReference(INTERNAL1V1);
#else
  analogReference(INTERNAL);
#endif

}

void presentation()  {
  sendSketchInfo("Soil Moisture Sensor Reverse Polarity", "1.0");
  present(CHILD_ID, S_HUM);
}

void loop() {

  measure(6, 7, 1);
 //  Serial.print ("\t");
 // Serial.println (average());
  long read1 = average();

  measure(7, 6, 0);
  //Serial.print ("\t");
  //Serial.println (average());
  long read2 = average();

  long sensor1 = (read1 + read2) / 2;

  /*Serial.print ("resistance bias =" );
  Serial.println (read1 - read2);
  Serial.print ("sensor bias compensated value = ");
  Serial.println (sensor1);
  Serial.println ();
  */
  //send back the values
  send(msg.set((long int)ceil(sensor1)));
  // delay until next measurement (msec)

  int sensorValue = analogRead(BATTERY_SENSE_PIN);
  //Serial.println(sensorValue);

  int batteryPcnt = sensorValue / 10;

  /*
  // DEBUG Battery INFO
  float batteryV  = sensorValue * 0.003363075;
   Serial.print("Battery Voltage: ");
   Serial.print(batteryV);
   Serial.println(" V");

   Serial.print("Battery percent: ");
   Serial.print(batteryPcnt);
   Serial.println(" %");
  // END DEBUG INFO
  */
  if (oldBatteryPcnt != batteryPcnt) {
    // Power up radio after sleep
    sendBatteryLevel(batteryPcnt);
    oldBatteryPcnt = batteryPcnt;
  }

  sleep(SLEEP_TIME);
}

void measure (int phase_b, int phase_a, int analog_input)
{
  // read sensor, filter, and calculate resistance value
  // Noise filter: median filter

  for (i = 0; i < NUM_READS; i++) {

    // Read 1 pair of voltage values
    digitalWrite(phase_a, HIGH);                 // set the voltage supply on
    delayMicroseconds(25);
    supplyVoltage = analogRead(analog_input);   // read the supply voltage
    delayMicroseconds(25);
    digitalWrite(phase_a, LOW);                  // set the voltage supply off
    delay(1);

    digitalWrite(phase_b, HIGH);                 // set the voltage supply on
    delayMicroseconds(25);
    sensorVoltage = analogRead(analog_input);   // read the sensor voltage
    delayMicroseconds(25);
    digitalWrite(phase_b, LOW);                  // set the voltage supply off

    // Calculate resistance
    // the 0.5 add-term is used to round to the nearest integer
    // Tip: no need to transform 0-1023 voltage value to 0-5 range, due to following fraction
    long resistance = (knownResistor * (supplyVoltage - sensorVoltage ) / sensorVoltage) ;

    delay(1);
    addReading(resistance);
    Serial.print (resistance);
    Serial.print ("\t");
  }
}

// Averaging algorithm
void addReading(long resistance) {
  buffer[index] = resistance;
  index++;
  if (index >= NUM_READS) index = 0;
}

long average() {
  long sum = 0;
  for (int i = 0; i < NUM_READS; i++) {
    sum += buffer[i];
  }
  return (long)(sum / NUM_READS);
}

scalz

Hello.

I think, depending on how your sensor is connected, it is always powered on. Your node is sleeping but you would need to use a mosfet to power off the sensor when you don't use it. Or use an IO pin to deliver the power instead of a "mosfet switch".

Martin Tellblom

@scalz said:

always powere

Alright, as you proberbly understand I'm not a electronics engineer :) so please explain that to me.
This is how its setup:

Everything is build on @sundberg84 Easy/Newbie PCB (This is my LAB PCB that I try out on before soldering, easier to chane components to see if someone of the cheap once are broken)

Sensor Vcc connected to 3,3V, GND to GND and sensor to D3.
So what do I have to do to turn of the sensor when I put the arduino to sleep?

alt text

sundberg84

@Martin-Tellblom - instead of wire power from VCC to the sensor you could try power it through D3 or another IO pin.
Then you set this pin to HIGH to power the sensor and then LOW before you sleep the node.

If you have a multimeter you could measure the ampere when you sleep the node.

Martin Tellblom

@sundberg84 said:

to HIGH to power the sensor and then LOW before you sleep the node.

If you have a multimeter

Alright so if I connect the Vcc sron the sensor to D2 (since I use D3 for measurement) and set that HIGH before I measure, should I have a sleep for it to power up aswell?

Something Like this?

  digitalWrite(SOIL_POWER_PIN , HIGH);  
  delayMicroseconds(25);

  moisture = analogRead(SOIL_SENSE_PIN);
  
  delayMicroseconds(25);
  digitalWrite(SOIL_POWER_PIN , LOW);

sundberg84

@Martin-Tellblom - Yes, something like that.
Dont use delay, use wait(); if tou want to create a pause for reading.

Martin Tellblom

@sundberg84
OK,

I have now changed to the below code and changed to a SOIL sensor with the LED still on

The LED is lit up even after digitalWrite(SOIL_POWER_PIN , LOW); so I don't think its working

void loop()
{

  digitalWrite(SOIL_POWER_PIN , HIGH);
  wait(25);

  moisture = analogRead(SOIL_SENSE_PIN);

  wait(25);
  digitalWrite(SOIL_POWER_PIN , LOW);

  if (oldMoisture != moisture) {
    send(msgSoil.set(moisture, 0));
    sendBatteryLevel(moisture);
    oldMoisture = moisture;
  }

  //Check Battery Level
  int sensorValue = analogRead(BATTERY_SENSE_PIN);

  int batteryPcnt = sensorValue / 10;
  if (oldBatteryPcnt != batteryPcnt) {
    // Power up radio after sleep
    sendBatteryLevel(batteryPcnt);
    oldBatteryPcnt = batteryPcnt;
  }
  digitalWrite(SOIL_POWER_PIN , LOW);
  digitalWrite(SOIL_POWER_PIN , LOW);
  sleep(SLEEP_TIME);
}

Martin Tellblom

@sundberg84

Stupid me, forgot defining it as output pinMode(SOIL_POWER_PIN, OUTPUT); in the setup

It's working now

sundberg84

Good! @Martin-Tellblom If you can measure how much uA it consumes in sleep() mode you can then calculate the life expectancy. Around 100uA is fine in my world with a booster and pro mini.

Martin Tellblom

@sundberg84 said:

can measure how much uA it consumes in s

I thought I could do that with my multimeter but I get no value

sundberg84

@Martin-Tellblom - Put the multimeter in series with VCC. Dont forget to change the input on your multimeter.

cimba007

@sundberg84

Be aware that depending on the mesurement range a multimeter could introduce a big burdan voltage.

Just simple and short: To measure in the mA range you the multmeter measures the voltage drop accross a series resistor with an value .. call it A.

Switching to the µA range the mutltimeter switches to a much larger resistor (e.g. 1000times A) to measure a significat enough voltage drop. With the wrong voltage range .. measuring µA while the board is consuming in the mA range might lead to a huge voltage drop and your circuit not working at all.

So do this:

Switch to mA mode .. take your measurement .. wait until you KNOW for sure your circuit is in sleep mode (add some messages on the serial console) and THEN switch to µA range.

Martin Tellblom

I don't think my multimeter is good enough for this, It seems like it put in some power due if I

I will try this when I get home today and see if I need a new multimeter or not :)

scalz

and with a multimeter only, due to burden voltage and depending of the multimeter precision, you won't get the true power consumption, an approx which is still nice, you can know what "looks" power consumption and tendancy. Even if you're using a nice expensive Fluke. Best precision for this is uCurrent Gold+multimeter ;)

Martin Tellblom

@scalz

Or just simply take percentage and date/time and then a few days later see what has changed percentage wise ...
Its to simple I know but if 1% battery power equals 4 days the sensor probably last for about 9-10 month (the last percentage I suppose you don't get any communication with :) )

sundberg84

@Martin-Tellblom - Im not sure it works that way. It depends on which battery you use.
Voltage tends to drop faster in the end for normal AA batteries.

My sensors doesnt drop that much (maybe 5%) the first 6 months.

Martin Tellblom

@sundberg84 Hmm What you are saying is that I need to buy a new and better Multimeter :) This is the reason I was waiting for ..... :9

sundberg84

@Martin-Tellblom - I hope you dont give up! Battery operations was the hardest part for me to figure out...

Martin Tellblom

I only have two kind of sensors that I need to be battery operated and that's the plants warning that they are out of water and soon gonna die and the dogs water bowl warning that they soon gonna die (KIDDING). The dogs bowl I like to measure the levels and have that to compare with the temperature, just for fun.
I hope I get this working aswell, It wont be pretty with a cable around the few plants we got

Nicklas Starkel

@Martin-Tellblom , I'm in this mess as well. Just ordered a new Multimeter off aliexpress :)

@sundberg84 , have you tried other batteries? I bough some ultrafire 3.7V 8800mAh and will try these.
They were cheap so no loss if they do not work out..

Battery powered sensor last 1 week

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