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Topic: Power Consumption of Atmega328P with ESP8266 and DHT11 (Read 1 time) previous topic - next topic

Korawy

Hi ALL,

I am implementing an IOT Project where sensor readings are transmitted online through wifi module (ESP8266).

The project works perfectly, and I was able to read DHT11 readings in (thingspeak.com) through ESP8266 module and a small atmega328p circuit (with arduino uno bootloader).

Now the most critical point is power consumption, it drives me crazy that I think of a small solar cell, but that's not preferable.

Even when using the deep sleep mode of atmega328p (and then ESP Module will be disabled), the regulator still have quiescent current of 5ma which will kill my battery in a week  (if i use 900mah battery),
and unfortunately in my country I cant find some low power regulators (draws micro Amperes).

Now Im thinking if I could attach a battery directly to my atmega328p and control the ESP and DHT through a transistor, so that the modules are completely disabled (the transistor is switched off) when the atmega328p is in power-down mode, and are enabled (the transistor is switched on) when the atmega328p wakes up.

Nick_Pyner

It seems that the sole purpose of the 328P is to manage power. Are you sure you need that? I thought the ESP8266 has its own power management facility.

musskopf

Here some an article about DHT11 and Wireless power consumption which might help: https://www.hackster.io/Talk2/temp-and-humidity-sensor-with-a-cr2032-for-over-1-year-580114, specially the part where you can optimize the DHT11 readings.

Also, ESP8266 is far from the best solution for low-power because of the very high power consumption of the WiFi module together with the long time it takes to start-up/join the WiFi network.
http://talk2.wisen.com.au

Korawy

It seems that the sole purpose of the 328P is to manage power. Are you sure you need that? I thought the ESP8266 has its own power management facility.
Atmega328P will send AT Commands to ESP8266 module, The both sleep modes of atmega or esp8266 are nearly consumping the same power.

Korawy

Here some an article about DHT11 and Wireless power consumption which might help: https://www.hackster.io/Talk2/temp-and-humidity-sensor-with-a-cr2032-for-over-1-year-580114, specially the part where you can optimize the DHT11 readings.

Also, ESP8266 is far from the best solution for low-power because of the very high power consumption of the WiFi module together with the long time it takes to start-up/join the WiFi network.
Unfortunately I dont have the whisper node in my country, but I do have NRF24L01 which is also a Low Power RF Module.

But Could the idea of using a switch transistor(controlled by atmega), that switches the power of my other modules work ??

Korawy

@musskopf

In addition this whisper node has a high cost.

musskopf

If you're worried with low power pick the NRF24 over the ESP8266... you can very quickly wake up the MCU, read the DHT11 (power if from the GPIO and sleep the MCU while it reads as explained in the article I've linked), wake up the NRF24 and transmit the data. Apart from the long time it takes to read the DHT11, the wake up and transmit can be done in less than 10ms. No need to power off the NRF24, sleep mode should significantly lower the current consumed by the module.

Now, if you're going to power via alkaline batteries, make sure you account for the voltage drop along the battery life... Remember that NRF24 does not tolerate anything over 3.6V, so you'll need a step-up from 2xAA to 3.3V or a low quiescent LDO/Step-down from 4xAA to 3.3V (3xAA might not work very well after 50-70% discharge because of the battery voltage drop).

Yes, the WN board used in the article is more expensive than an Arduino, but it basically adds-up the cost of all components: RFM69: $4; Arduino Mini Pro: $2.5 - $3; Step-up Regulator: $3.5; 4Mbit Flash: $2 - $3; SMA 2dBi Whip Antenna: $5 - $8; SMA Connector + LEDs + Buttons: $3 - $4; PCB Headers + Passives: $1.5... Total $21.5+?! At the end, all depends if you wish to spend time building everything or start from a ready-to-use solution.
http://talk2.wisen.com.au

Korawy

Thanks Musskopf,

The most problem I face here is the power consumption, as in my country I cant find low quiescent current regulators.

But in your reply you mentioned step up module,still it must have a small quiescent current i think ?!

Also regarding the batteries used, Im using 4 AAA Ni-mh batteries, Do those batteries are consumed over time even when they are not used (no load) ?

Im asking that to know the approximating working time when im making my calculations..


musskopf

How long to wish to have your project running without replacing batteries?

The quiescent from a good regulator, step-up or LDO will be under 10uA, which is probably less than an Alkaline self-discharge. If you need batteries to last more than 3-6 months stays away from rechargeable cells and the self-discharge is significantly bigger: http://batteryuniversity.com/learn/article/elevating_self_discharge

Finally, can't you buy anything Internationally? Ebay, Aliexpress?
http://talk2.wisen.com.au

Korawy

Thanks musskopf,

I need to replace batteries every 1 year or so.

Your Link is very useful, I was looking for a similar one, So it seems that primary lithium-metal or alkaline batteries are the best choice.

Surely, I can buy anything internationally, but the matter of time and i dont want to order something and then change it due to other problems.


Korawy

@musskopf

May I know a good regulator or step down/up module with a low quiscent current (under 10uA)?!

musskopf

Which output current do you need and whats the expected input voltage range and output voltage?
http://talk2.wisen.com.au

Korawy

Using ESP Module is recommended as its performance is better, and also it can be used as a standalone device, Im planning to use ESP with a sensor (can be DHT or Moisture Sensor).
ESP power is 3.3v and most sensors work with 5v, So I will use a >5v battery with the sensor (regulated) and a regulated 3.3v with ESP, so that they communicate to each other through a level shifter.

In order to save power, I am thinking to control power of other devices through esp8266, that is, when the module is in transmission mode, it will enable the power of other devices through a transistor or optocoupler and when in sleep mode, it will completely disable other devices.

-Output Current cannot exceed 300ma or so, however a regualtor with at least 800ma output current is preferred.
-Input voltage >5v battery.
-Output voltage regulated 5v and 3.3v.

Thanks

habanero

I'm actually about to start using a similar sensor node I've built to take remote readings for my Arduino-based weather station. I have 2 versions of it, one using a Pro Mini and the other a Nano, and both connect to the base station via an RF24+ module. Both have a DHT22 sensor for T/H and an LDR for light levels. The Nano version also has an MQ-2 gas sensor, which adds quite a bit to the power consumption.

I designed it to run off either a battery or 5V adapter, but I might want to install one of these outdoors, where it would be preferable to run it off solar. I think I've figured out how to make this work, in terms of boards needed to charge the battery (so it works at night and when overcast) and step up the voltage, but I'm not sure what battery capacity I'd need. It's going to be a 3.7V LiPo, but I have no idea how much capacity it'll need. Any ideas? I posted separately in this forum with more details, but saw this thread so I thought I'd ask.

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