Battery Sensor with stepup and on/off transistor

n3ro

Hey Guys,

Today I had an idea how you can save some power on battery sensors.

I simply connected a transistor before a StepUp converter. So the stepup and the connected sensors only supplied with power when they are needed.

My stepup + DHT11 has power consumption at 90 uA when sleeping. By disabling with the transistor it goes against 0.

Do you think that might help a little?

Best Regards,
n3ro

#include <SPI.h>
#include <MySensor.h>
#include <DHT.h>

#define CHILD_ID_HUM 0
#define CHILD_ID_TEMP 1
#define HUMIDITY_SENSOR_DIGITAL_PIN 4
#define STEPUP_PIN 5                 // Transistor connected PIN   
unsigned long SLEEP_TIME = 10000; // Sleep time between reads (in milliseconds)

MySensor gw;
DHT dht;
float lastTemp;
float lastHum;
boolean metric = true;
MyMessage msgHum(CHILD_ID_HUM, V_HUM);
MyMessage msgTemp(CHILD_ID_TEMP, V_TEMP);


void setup()
{
  gw.begin();
  dht.setup(HUMIDITY_SENSOR_DIGITAL_PIN);

  // Send the Sketch Version Information to the Gateway
  gw.sendSketchInfo("Humidity", "1.0");

  // Register all sensors to gw (they will be created as child devices)
  gw.present(CHILD_ID_HUM, S_HUM);
  gw.present(CHILD_ID_TEMP, S_TEMP);

  metric = gw.getConfig().isMetric;
}

void loop()
{
  stepup(true);
  delay(dht.getMinimumSamplingPeriod());

  float temperature = dht.getTemperature();
  if (isnan(temperature)) {
    Serial.println("Failed reading temperature from DHT");
  } else if (temperature != lastTemp) {
    lastTemp = temperature;
    if (!metric) {
      temperature = dht.toFahrenheit(temperature);
    }
    gw.send(msgTemp.set(temperature, 1));

  }
  Serial.print("T: ");
  Serial.println(temperature);

  float humidity = dht.getHumidity();
  if (isnan(humidity)) {
    Serial.println("Failed reading humidity from DHT");
  } else if (humidity != lastHum) {
    lastHum = humidity;
    gw.send(msgHum.set(humidity, 1));
  }
  Serial.print("H: ");
  Serial.println(humidity);
  stepup(false);
  gw.sleep(SLEEP_TIME); //sleep a bit
}

void stepup(boolean onoff)
{
  pinMode(STEPUP_PIN, OUTPUT);      // sets the pin as output
  Serial.print("---------- StepUp: ");
  if (onoff == true)
  {
    Serial.println("ON");
    digitalWrite(STEPUP_PIN, HIGH);      // turn on
  }
  else
  {
    Serial.println("OFF");
    digitalWrite(STEPUP_PIN, LOW);       // turn off
  }
}

hek

Yep, will probably prolong battery life. Just remember that some sensors needs to be reinitialised when you power them on. I have not analysed what dht.setup() does in your case.

n3ro

@hek In my tests its working with DHT11 and DHT22. Maybe a MQ-2 works too, but a MQ needs 2 minutes heatup time.. :-/

scalz

Hi,

your tests are interesting. I am trying to do same thing. But cannot test for the moment, I am waiting for components.
I designed another little board with only dc booster and power management. then just connect to arduino existing node . I have to do some tests before release files. but if you want to test, you can see theory here http://forum.mysensors.org/topic/1419/sensor-board-with-booster-and-supervisor/1

RJ_Make

@n3ro What transistor are you using? I thought someone already did some testing and found that the start up power was too expensive in over the long run? (sleep Vs cold start) Maybe I misunderstood the result of their test though...

n3ro

@ServiceXp is use this: LINK

n3ro

@ServiceXp could you already test cold start vs sleep?

RJ_Make

@n3ro

I didn't do the testing, I just thought I remembered reading some information from someone who did. I can't find it though, so it may have been my imagination... :no_mouth:

? Offline

Hello n3ro ,

witch stepup converter you use? Where is your NRF24L01 connected? Sirctly to the battery? Can you explain your wirings? I plan a DHT22 sensor with NRF24L01 and 3.7V Lipo with charger

n3ro

@ht81 Hey, the NRF is directly connected to the battery. only the DHT use the stepup.

i use this stepup: http://www.banggood.com/2Pcs-500mA-DC-DC-1V-5V-Converter-Step-Up-Module-Power-Module-p-945167.html

Just put a transistor in front of the stepup. this is all :)

ahhk

Hi,

this is interesting. What about the HIGH-Levels in this scenario in genereal? DHT is powered at 3.3V and ATMEGA is powered by batterie (e.g. 2.8V?). Isn this a problem when the high levels are different? DHT high is higher then atmega-high-level (3.3V => e.g. 2.8V).
If not it could be a very nice solution to power only the sensors via a step-up-regulator - connected to arduino pin (or via transistor) :)
Greetings

Andreas

n3ro

I use this setup at the moment and it works. the arduino is still alive :D

? Offline

Hi,

how many batteries do you use? the Arduino requires at least 3.3V or? You stepup to 5V for the DHT22, right? Last question, how long works your node with a battery pack? 2 Month?

n3ro

i have only a test setup at the moment with 2 AAA batteries. So i cant give you a battery lifetime :/

I use a arduino 3.3v and the stepup pushes the voltage to 5v for the DHT.

Harrdy

@n3ro said:

i have only a test setup at the moment with 2 AAA batteries. So i cant give you a battery lifetime :/

I use a arduino 3.3v and the stepup pushes the voltage to 5v for the DHT.

can you tell me why u push the voltage to 5v? the dht works great with 3.3v

n3ro

@Harrdy the stepup with 5v output is much cheaper ;)

? Offline

Ok,
is it possible to supply the arduino, NRF and DHT directly from an 3,7V LiPo? Your 2N2222A as an Switch for the DHT Power Pin? Can you tell me, what is the current consumption of NRF, and Arduino during Sleep mode by code "gw.sleep"

n3ro

@ht81

hmm the max voltage of the NRF is 3.6v (https://www.sparkfun.com/datasheets/Components/SMD/nRF24L01Pluss_Preliminary_Product_Specification_v1_0.pdf)
maybe the NRF is broker after 3.7v. i dont know...

the 2N2222A turns the stepup on and off. the DHT is direct connected to the stepup.

you can read many stuff about the power consumption of NRF+Arduino in the forum. With modified fuses and cutted LED+power regulator ~40uA

BastienVH

@n3ro
I have been looking into making some battery powered sensors.
I have some questions about your setup, because I've been looking for some step up convertors but the 3.3v seems so expensive compared to the step up your using (I've only found this 3.3v one) which is 3+ times more expensive than this 5v one).

Do you power your pro mini 3.3v from the 5v step up?
Did you remove the on board power regulator (I'm thinking you haven't)?
Does your DHT sensor work fine with 5v?

I've been breaking my head over how to make the cheapest battery powered sensor possible, but it's been difficult since I'm very much still a noob.

GertSanders

If one uses a LiPo battery giving (officially) 3.7V, it could be higher when it is new. I would suggest putting a Schottky diode (like 1N4001 of 1N4007) between positive of battery and VCC of NRF24. This way you force a voltage drop of minimal 0,5V and under load this goes up to 1V. The NRF24 works perfectly fine like this.
I have a setup where I feed the atmega328p and a SIM800L with 4V, the NRF24 gets around 3.4V at startup, and under load around 3.1V

Battery Sensor with stepup and on/off transistor

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