Stupid Weatherbox on E-Ink

Already a year and a half ago, I bought a pair of E-Ink screens with eBay based on the SSD1606 driver, just for the weather station. And 4 months ago, before the new year, he appeared.

I will say at once that there is no clock in it, since at home there are literally watches everywhere But he can show the following:

• current temperature Celsius;
• current humidity in percent;
• current pressure in mm Hg;
• pressure history for the last 15 hours as a graph;
• battery voltage.

Actually, that's all. The necessary minimum and ultimate simplicity!
')

Principle of operation

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The controller should at the touch of a button to display current information. Most of the time the controller sleeps, as does the display, which is in deep sleep.

The controller periodically wakes up on watchDog and once every 5 minutes makes pressure measurements, to build a graph of pressure changes.

With the schedule came out very interesting, since the pressure can change very quickly and strongly (the weather in the northern city is generally unpredictable), then at some point a graph may increase in scale. To do this, once a couple of hours, the average measurement point is recalibrated (the pressure can go both up and down). However, due to this, the visual difference of the previous values ​​simplifies the reading of the graph (example on KPDV).

Iron

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The main brain is the ATMega328P microcontroller, the BME280 is used as an all- meter barometer, and for the screen the previously described E-Ink second revision based on SSD1606 from Smart-Prototyping.

This is almost the same screen as waveShare epaper 2.7 “, only older (they have very similar datasheets).

All this works on the battery from a toy helicopter at 120 mAh. The battery is charged using a module with protection against deep discharge and recharging on the basis of TP4056 with a 47 kΩ resistor installed for charging current of about 20mA.

Energy Optimization

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Good and healthy sleep is our everything! Therefore, you need to sleep to the maximum!

Since there was no software for working with the screen, only a basic code sample with comments in the language of the Middle Kingdom and datasheet (the screen just appeared a year and a half ago), I had to do most of the work myself, since there was already experience with different screens.

The DeepSleep mode was found in the datasheet, the screen consumes nothing but 1.6mA in it!

The barometer has a metering mode on demand (aka standby), in it the sensor consumes a minimum of energy, while providing sufficient accuracy for simple indication of changes (in the datasheet it is indicated that it is just for weather stations). The inclusion of this mode gave a consumption of 6.2 μA. Next on the module was the LDO controller with the LM6206N3 (and maybe the XC6206, both of them disguised as 662k) on the MCP1700.



This gave a gain of even 2 µA.

Since you need to achieve minimal power consumption, the LowPower library was used. It has a convenient work with watchDog, on the basis of which the dream is made. However, by itself, it consumes about 4µA. I see a solution to this problem using an external timer based on Texas Instruments TPL5010 or similar.

To reduce power consumption, it was also necessary to flash the tool with other FUSE bits and a bootloader, which was successfully done with USBasp, and was added to the boards.txt file


Also put in the “bootloaders / atmega /” folder the bootloader compiled from optiboot:


Actually, as you most likely guessed, all this was done on the basis of the Arduino, namely pro mini at 8 MHz 3.3V. The mic5203 LDO controller (too voracious at low currents) was dropped from this board and the LED resistor was sealed off to indicate power.

As a result, it was possible to achieve energy consumption of 10 µAh in sleep mode, which gives about 462.96 days of work. It is safe to deduct a third from this number, thereby obtaining about 10 months, which so far corresponds to reality.

I tested the version on ionistors, with a final capacity of 3 mAh, it works no more than 6 days (high self-discharge). The calculation of the capacity of the ionistor was made according to the formula C * V / 3.6 = X mAh. I think that the version with the solar battery and MSP430 will be generally eternal.

Housing

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Since I do not have a 3D printer, but I have a MyRiwell RP800A 3D pen. It turned out that it was not so easy for her to make planar and even structures. All PLA was painted with plastic, which was at that time, so the case came out multi-colored, which in other matters gives a certain charm (then I will redo it under the tree, when plastic with wood chips comes).

The first parts were drawn directly on paper, after which they came off. It left traces on the plastic. Moreover, the details were crooked and needed to be straightened somehow!



The solution turned out to be trivially simple - to draw on the glass, and under it put "drawings" of the necessary elements of the body.

And that's what happened:



The screen update button just had to be red on a white background!



The back wall is made with a simple pattern, thereby creating air vents.



The button was attached to the horizontal strut inside (in yellow) with the handle that was also made.



The button itself is taken from the old computer case (it has a pleasant sound).



Inside, everything is fixed with hot melt and plastic, so that it’s not easy to disassemble.



Of course, left the connector for charging and firmware upgrades. The case, unfortunately, had to be made monolithic for greater strength.

Conclusion

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4 months have passed, and after not fully charging (up to 4V) the voltage on the battery is only up to 3.58V, which guarantees a long service life until the next charge.

People are very accustomed to this thing in the case of headaches or if you need to know the exact weather forecast for the next hour or two, they immediately go to her and see what happened with the pressure. At KPDV, for example, one can see a strong drop in pressure, as a result it began to snow heavily with the wind.

Repository links:

→ screen library
→ library for lowPower
→ library for BME280

Updated:

In connection with the increased interest in the body posted more images. Screen Smart-Prototyping second revision. Analog to him on Ali here .


PS KPDV was done in the evening, as a result, very, very much snow fell in St. Petersburg tonight.
PPS Blue tape did not add to the survey for known reasons.