Sensors and PCB Design
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Just have a energy regulator that converts the 5V from the USB connector to the 3.3V for the remainder of the board. Since all of the sophisticated ESP8266 circuitry is already dealt with on the SoM I used and the USB-to-serial converter is laid out, the rest is simple connectors. Probably the most problematic one is that I put zener diodes on the UART lines between the USB-to-serial converter and the ESP module. To make things worse the diodes are utterly pointless for this because the uart lines will not leak energy in deep sleep anyway. Some datasheets even have bits of advisable PCB layout in it to make the PCB layout easier. Most of this design work is just reading the datasheets for the parts and following the recommendations there. In this design it's programmed to charge at 400mA which isn't tremendous quick however it should last some months on a single cost anyway. With this it is only a single button and the Kicad file will probably be despatched off to Aisler the place their servers will generate the necessary fabrication information from it. The MOSFET will disconnect the battery power when 5V is provided and the diode makes sure that the facility of the battery will not ever circulate again into the 5V a part of the schematic.
I additionally forgot so as to add the thermal relief specified within the structure strategies of the part so while charging that chip is practically continuously at 80°C making the worth of the temperature sensor elevate by round 5°C. Since this only affects the board when the battery is charging it's not a important fault. Most of my exterior sensor boards are already temperature/humidity sensors so it makes sense to only include it since it's an inexpensive chip. A customized board that makes it easy to connect my present sensors and allows a bit of extension. A few of the sensors I want are even out there as pmod modules. In some instances it's easy enough to only stick the modules on a bit of protoboard and solder it collectively. I unnoticed all of the half numberes for the through-gap parts since these are either costlier or inconceivable to assemble and likewise pretty easy to solder manually if required on that particular board. Luckily this is definitely fixable on my boards by making a solder bridge across the diodes.
Making boards is fun. For the battery operated boards that wouldn't be sufficient though. The protection chip sits between the bottom terminal of the battery and the precise board ground and disconnects the battery pack in case of overcurrent, brief circuits, overcharge or undercharge. On this case the board was designed because I needed 15 of this design and this makes a lot more reliable and straightforward to take care of with the likelihood to have neat screw terminals on it for the external connections. The design is based around an ESP-12F module since all my current sensor code is already written for the varied ESP8266 boards. It's pretty basic firmware that does the usual WiFi connection things for the ESP module and connects to my MQTT server to push the sensor readings in a loop. With that firmware the battery would run out in hours. The board itself is extremely simple but it did give me an opportunity to run via the entire strategy of going from a schematic to an actual physical product. One simple change from the nodeMCU design is that I swapped the USB Micro-B connector for a kind-C connector which requires a bit more PCB routing to deal with the reversable plug and two further resistors to make it as much as USB spec.
Most of the problem with this design is determining the ability design. The diagram above shows the ultimate power design. The result's that the ultimate battery level graph is a bit choppy however a minimum of it features. During deep sleep the entire board makes use of 19.1µA with a half charged battery in my tests and the transmission is down to to a bit less than a second at 70mA, but the ability use of the transmissions varies quite a lot. There's a great sequence of weblog posts from Oppoverbakke that go into great detail on the way to optimize deep sleep on the ESP module. I dropped the auto-reset circuit since I was frightened it might interfere with the deep sleep reset circuit that I found more vital. The software on the ESP will have to first enable the measuring circuit by toggleing a gpio, reading the worth with the ADC after which disableing the gpio again. The issue of that is that the resistor divider will not solely do the voltage scaling for the ADC however will even be a path for the battery to leak power. Then with that information the module will save round one second of time being awake and connecting.