My design is meant to be used outside the home. I wanted the platform to be able to “sleep” for extreme lengths of time at ultra-low current. The platform needed to be somewhat universal. I wanted to monitor the environments temperature and voltages. I also included connections for soft serial in case we wanted to include a GPS.
Here is a block diagram of the design:
The heart of the platform obviously is the ESP8266. I used the Arduino IDE to do my coding with JChristensen’s MCP980X library.
I find the ESP8266 to be extremely robust and powerful for the various projects I have built.
I used a Microchip MCP7940 I2C RTC as a programmable alarm to enable the power supply. This allowed me to set off times as long as a month if I want but I have mostly been off 1 to 6 hrs. The off current for the platform is around 750na while just powering the RTC bat circuit. The RTC Multi-function pin is used to hold down the EN pin of the boost regulator/switch.
This platform is using a boost regulator so I can run off a 3 volt AA battery and a Solar cell. I am using a Microchip MCP1640 boost regulator that is configured to boost and regulate at 3.3v. This circuit allows the battery to go down to ~1v and still regulate at 3.3. The Solar cell backfills the battery on sunny days. I have been running this configuration in excess of a month with great success.
There is a Microchip MCP3221 i2c SOT23-5 A to D on the platform that I use to monitor the battery voltage. It is a single input device and can be used to report all sorts of things from water levels to light levels. Issues found: I was reading stable values except every once in a while. I believe the issue was with the I2C pull ups as a result I stiffened them. My intent is to use this to sense various items in a greenhouse.
I used a Microchip MCP9800 SOT23-5 I2C temp sensor for the onboard temp.
Here is a close up of the finished working PCA.
I used ThingSpeak as a network sensor database. I used the sample Arduino code to set up my wireless link and start up the client. I then formed up a URL of the appropriate construct that Thingspeak expects. Here is an example where the voltage and temperatures are sensed every 15 minutes unless the voltage is below a limit where the off time is extended to reduce current usage.
I need to give a shout out to the Community for all the great work they are doing supporting the ESP8266 and Arduino environment. I was also lucky to find a real responsive board manufacturing group PCB-Way.com. It is incredible what an individual can produce these days using common resources.
Feel free to contact me if you have any questions.
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