Over the last year I have standardised on the ESP8266 for all my small IoT projects. Its low price, ease of use (now that the Arduino IDE is available), tiny size and built in Wi-Fi makes it a compelling option.

Using Wi-Fi is a convenient way to link your newly created IoT device into your existing IT infrastructure – including cloud services – but it also has a drawback. Wi-Fi’s demand for power usually makes battery operation impractical for any real deployment. I have been able to get around this issue for most of my projects (e.g. the train and the smart shelf described on this blog) because they are for demonstration purposes only, requiring the battery to last no longer than a few hours.

Nevertheless, it is possible to put the ESP8266 into deep sleep and wake up periodically to check and activate Wi-Fi only when required. This would suit a scenario in which an IoT sensor sends relatively infrequent one way traffic (i.e. where real time control of the device is not needed).  I wrote about the ESP8266 deep sleep option more than a year ago, but have not explored it any more until recently, when exactly such a project arose.

The other thing that I have done over the last year is to standardise on using the NodeMCU (hardware, not the LUA software). Especially when rolling out multiple small projects, it is immensely convenient to be able to plug a device into a USB port and just program it (automatically without having to wire up serial pins and then get the correct pins tied high / low for flashing / running). With no need to worry about providing 3.3V power, adding capacitors to prevent the ESP8266 power spikes from causing instability, or adding a resistor + cap for a power-on reset. No need to scale down the ADC input to 1V or to add my own test led… and all of this in a breadboard friendly package.

Also, just to be clear for those who may wish to follow along, I always use the “second generation” NodeMCU known as v2. The different versions are described here and I agree with that poster – i.e. don’t buy the v3 variant because its larger size means that it leaves no free breadboard holes on either side.

Unfortunately, with all this added convenience comes the drawback of added power consumption, which continues even when the ESP8266 is in deep sleep.

I measured 18mA to the NodeMCU board while the ESP8266 was in deep sleep mode – orders of magnitude more power hungry than I was looking for.

So for my iot-container project, I sought to retain the convenience of using the NodeMCU, but to address its power consumption shortcomings to allow battery operation.

Read further to hear what I did. Continue reading →