Recently, I added solar power to one of my ESP8266 weather stations.
With the right hardware, this was actually remarkably easy to do. To make things nice and easy, I ordered an Adafruit USB/DC/Solar Li-Ion/Li-Poly charger. (Top-right in the photo) These boards can take DC input from USB, a 2.1mm power jack or from wires soldered directly onto the board. It will then both charge a Li-poly battery and power a load. Whatever power is left over from powering the load will be used to charge the battery, and if the load draws more than what the solar panel can provide, the rest will be drawn from the battery.
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Last month I wrote a series of posts about reducing the power consumption of the ESP8266, showing how I got the power consumption of a weather station down to 54 μAh per 5 minute reporting cycle.
At the end of that, I thought further improvements would be mainly tweaks and fine tuning, but Tobias wrote a comment explaining that it would be possible to avoid the initial network scan happening as part of the WiFi network association. I’m happy to say that it is possible, and it works quite well indeed.
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This is a post to explain the basics of electronics, starting with Ohm’s law.
Ohm’s law describes the relationship between the voltage, current and resistance in a circuit, and it is one of the basic physical laws that controls how circuits work.
We need to understand this law in order to select the correct resistors to use in our circuits and to control how much current will flow. We also need to know how much power our circuit will draw and how much power each component will dissipate. Too much power and things will heat up too much, burning out.
And yes, this post does contain garden hoses…
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As part of my recent projects, I have started including OTA firmware updates for my ESP8266 devices. (Also known as FOTA)
Doing so is actually remarkably easy, thanks to the very good support for this exposed by the Arduino board support package. The hardest thing actually becomes getting the web server side set up, rather than the changes required on the device itself.
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By carefully rearranging the operations my weather station does each time it wakes up, I have reduced the power consumption even further.
As it wakes up, it needs to make a series of measurements:
- Read the current battery voltage
- Read the current temperature from a DHT22
- Read the current humidity from a DHT22
- Read the current temperature from a BMP180
- Read the current air pressure from a BMP180
The battery voltage is read through a resistor voltage divider feeding into the analog input of the ESP8266. This reading is very sensitive, and a massive power drain from the WiFi function will bring down the measured voltage. This can be mitigated by using capacitors to buffer the analog readings, but if I have a choice I’d still prefer to have the WiFi function off when reading this.
The rest of the readings, however, are digital and not that sensitive to overall system power drain, and that gives us an opportunity to do things in parallel.
Continue reading “Further reducing power consumption on ESP8266”