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How to make a cool ink screen electronic clock?

2022-07-05 01:49:00 【Chip home】

This week I will introduce to you a beautiful ink screen electronic clock , It has the function of meteorological station （ Can pass GPS Automatic setting ）, use 4 section AAA Battery life 6 About a month or so , and , To ensure safety and reliability , It doesn't require any network connection .

Features include ：

Automatic setting （ adopt GPS）
Current temperature .
The current humidity .
Show past 25 Pressure chart of the pressure within hours .
Sunrise and sunset time
The current phase of the moon
stay 12 Hours or 24 Select between hour modes .
Choose between English and metric units .

This project has two different versions , Namely “ Simple and easy ” edition and “ Low power ” edition .

“ Simple and easy ” edition Is based on Arduino Nano Of . The aim of this version is to minimize the cost 、 The number of parts and the complexity of fabrication ; The downside is that you need to use a USB 5V Adapter to power the clock .

“ Low power ” edition Use one 32k The oscillator , Maintain accurate timing with minimal power . This oscillator allows the clock to run on batteries .

The first 1 Step ：" Simple and easy " Revision parts list

Arduino Nano
Waveshare 2.9 in EPaper modular
Adafruit MS8607 pressure / humidity / Temperature sensor
Anything with a 9600 Baud TX Of GPS modular
Circuit board （ It can be a prototype board or a piece for CNC Copper plate ）
Several button switches （ To change UTC Time offset and display preferences ）
The material used to make the shell （ At the end of the article, there will be .3mf、.scad and .dxf file )
USB Charger and charging cable

The first 2 Step ：" Low power " edition

These materials are the same as the simple version above ：

Waveshare 2.9 in EPaper Module
Adafruit MS8607 pressure / humidity / Temperature sensor
Circuit board
Several button switches
The material used to make the shell

Besides , You also need to ：

Atmega328P DIP edition （ You can also choose SMD Packaged version , But in 32K It will be more difficult to weld on the crystal ）
32768 Hz Crystal （ This oscillator is the key to low power design ）
Adafruit GPS modular （ This module is better than " Simple and easy " The quality of modules in the version should be higher , Because it can track more satellites （ To lock faster ）, Provide an enable pin （ For low power consumption ） And a port to keep its memory active （ For quick re locking ）. If all these features are not worth the cost to you , You can add your own enablers FET, Magic changes a cheaper module to complete this work . How to do this will be explained later ）
LED+ resistance （ Naked Atmega328P There's no way to tell you if it's working , Flashing lights can provide a 1ms/ Of a second " heartbeat ", Almost no power consumption , But it provides useful feedback ）
How many? 10uF and 100nF To smooth the supply voltage
The battery （ I use it 4 individual AAA The battery , But anything that can be obtained 5-7 A battery with a voltage of 25 volts can be used ）
（ Optional ） One is used to pass through ICSP To program a chip 3x2 syringe needle （ If you can remove Atmega328P reprogramming , Then you can skip this connector ）
（ Optional ） One for the UART Debugging 1x2 Pin connector （ This is only required if the board is unstable ）

The first 3 Step ：Arduino Mini edition

As mentioned above, there are two versions , This is an extra version , The reason why there is such an extra version , It is because we are now in " Shortage of parts ", image Atmega328P Such chips will be out of stock for a long time .

You can use it. " Simple " Version of the firmware runs this version , perhaps , If you have confidence in your welding skills , You can weld one on the microcontroller 32k The crystal of （ As shown in the figure above ）, And use 32k Version of the firmware （ See the next section for more details ）.

The above schematic diagram uses a " cheap GPS " Solutions to connect , But if you use something else （ such as Adafruit） In the schematic diagram GPS part , You can also use other （ such as Adafruit Of ）GPS（ As shown in the schematic diagram of the previous step ）.

The first 4 Step ： cheap GPS（ Optional ）

With competitors （12 dollar ） comparison ,Adafruit Of GPS The device is very expensive （30 dollar ）. If you think the added features （ It is described in the section of low power components ） No " Worth ", You can put anything you can with 9600 Baud transmission NMEA A string of GPS Throw the module in （ Most of the GPS All modules are OK ）.

But now there is a new problem to be solved ： Most of these units lack an enable / Disable pin , and GPS The unit usually consumes 30-100 Milliamperes of electricity . We can use one N-MOSFET（ Or similar ） Black out a disable switch . The schematic diagram above shows the basic idea . We can also do that falstad^[1] Try to .

This power switch circuit has a trade-off . If you are interested in more details , Please see Appendix B.

The first 5 Step ： Low power hardware modification

If you are making " Simple and easy " edition , You don't need to read this part . about “ Low power ” edition , These modifications will greatly improve battery life .

To illustrate , We will assume that the power supply comes from a set of AAA The battery , Can provide 1000 mah . Let's assume that you are using 32K Of Adafruit edition , And no changes have been made . The following is an example of power decomposition .

" sleep / close " CPU、GPS、MS8607 and EPaper： The measured value is 30-70uA（ We think it's 50uA）.
Screen update ：5 Ma , Every minute 2 Seconds at a time ：5 * 2 / 60 = 166 uA
GPS to update ： Once a day , Every time 50 Ma , Every time 10 second .50 * 10 / 86400 = 6 uA
MS8607 LED：100 uA
Adafruit GPS Pull up resistance ：500 uA

therefore , We have （50 + 166 + 6 + 100 + 500）= 822 uA Average current consumption , It's about 50 Days of power .

If you remove MS8607 LED and GPS Pull up resistance , Our electricity consumption will be reduced to 222 uA, That is about 187 Days of electricity consumption , It greatly increases the use time .

1、 First , Recommend from MS8607 Remove LED（ The details are shown in the figure above ）

2、Adafruit GPS The pull-up resistance on the is caused by Adafruit Added by the designer of , bring EN The pin becomes an option . But it also has a disadvantage , When you pull it to the ground （ Ban GPS） when , There are about 500uA The current of is consumed in the pull-up resistor . Since the enabling pin of this design is actively driven , You can remove this resistor （ The details are shown in the figure above ）

3、 Professional Mini modification . Search engine search "Arduino mini low power consumption " Learn more , Basically , You will want to remove the voltage regulator and LED, To reduce power usage . We switch to MS8607 Voltage regulator of （3.3V, Lost in idle time 35-55uA Power ） by pro mini Power supply .

4、 stay pro mini In the picture of , I also removed the crystal oscillator , by 32K The chip of the crystal is ready . Only in 32K In the case of the crystal version, this crystal is removed , And only on pro mini The inner fuse of the is reprogrammed and then removed , It will be explained later .

The first 6 Step ： The firmware

In this step , I have attached nano and 32k Crystal version .hex file （ Both versions apply to pro-mini, If you're not sure which version to use , Just use nano edition ）.

If you want to build your own / Modify the source code , You can visit GitHub：https://github.com/mattwach/epaper_clock

Build yourself .hex Firmware file （ Optional ）

Be careful , This code does not use Arduino library , Because the generated code is too large , Cannot be in Atmega328P Installation on （ And this is my personal preference ）. It is to use C language-written , Used Arduino^[2] Also used AVR Base library as the base . If you want to compile code , You need to install （ Free of charge ）avr-gcc Tools ^[3], clone epaper project ^[4] Source code . Then enter firmware/^[5] Directory and enter .

make

If the code establishes , Can open Makefile^[6], Look at these options .

# This is the Low-power stand alone chip configuration.
CLOCK_MODE ?= USE_32K_CRYSTAL
UART_MODE ?= HARDWARE_UART
F_CPU ?= 8000000

# This is the easy-to-build firmware that is based on an Ardino Nano
#CLOCK_MODE ?= USE_CPU_CRYSTAL
#UART_MODE ?= SOFTWARE_UART
#F_CPU ?= 16000000

If you're building 32k Crystal firmware , The configuration is correct . If you build nano Version of , You need notes 32k Period , uncomment nano That code , Then again, make.

There is also a special debugging mode , Through hardware UART With 9600 Baud's speed dump log information . You can now ignore , But remember it , Because it may be useful in the future .

# Uncomment to activate debug via the UART TX (9600 baud)
#DEBUG_CFLAG := -DDEBUG

Last , You can decide by changing several variables GPS How long should it be activated . Run once a day by default , But if GPS It takes a long time to lock , It will reduce the operating frequency , So as to reduce battery consumption . Please be there. src/gps.c^[7] Read all relevant content in .

This part of the file can be downloaded at the end of the text ！

The first 7 Step ： Use ICSP Upload firmware

This section is for those who upload code to a standalone Atmega328P The little partner of the chip prepared , If you want to upload to Arduino Nano, Please skip to the next step .

You need one ISP（ or ICSP） The programmer . You can use a spare one Aruino Uno/Nano Make one of your own . You can search in search engines "Arduino ISP Programmer" Please note that , Many of these guidelines assume that your real goal is to install a bootstrap , But for us , No bootstrap required , Because we will use ICSP Upload .hex file .

Power off detection

In my Atmega328P On , Power off detection is set to 3.5V（ It looks like an old version ）, So I use this command to disable power-off detection .

/usr/bin/avrdude -patmega328p -cusbasp -Uefuse:w:0xFF:m

Your may be different , It depends on your “ISP programmer”（-c Options ）. It's also possible that you don't need to set , Just in case .

The first 8 Step ： Use Avrdude

We can use one called avrdude Free tools , To upload the hex file it created to your Uno/Nano/. We can also download and use directly from the command line avrdude.

use Arduino IDE Run an upload with the output record open （ Light up demo Or something demo）, Then copy the commands it uses . perhaps
Read the official avrdude file ^[8] perhaps
Read reference online to use avrdude A tutorial for

This is where I am nano Used in version avrdude command （ adopt make Upload ）.

For reference ：

/usr/bin/avrdude \
  -v \
  -patmega328p \
  -carduino \
  -P/dev/ttyUSB0 \
  -b57600 \
  -D \
  -Uflash:w:epaper_firmware_using_arduino_nano.hex:i

This is me in ISP Used in version ：

/usr/bin/avrdude \
  -v \
  -patmega328p \
  -cusbasp \
  -Uflash:w:epaper_firmware_using_32k_crystal.hex:i

What we use here is Linux.Mac and Windows And it works , But like -P Such options will be different （ That is to say Windows It could be -PCOM1）.

Again , This part of the document can be found in Download at the end of the article ！

The first 9 Step ：32K Crystal oscillator

If you are making " Simple and easy " edition , Please skip this step . If you're using 32k Crystal firmware , You need to install crystals to make the firmware work .

First （！） You also need to configure ATMega328P Internal fuse of , To use internal 8Mhz Crystal .

It's important to do this first , because 32K The crystal will replace any existing crystal . If you don't change these fuses , The chip will become unresponsive , Until you reconnect one 8 or 16Mhz The oscillator .

as far as I am concerned ,Arduino pro mini Also needed ISP To change the inner fuse （ But I could be wrong ）. I looked it up "Arduino ISP", To get the correct pin mapping , So that ISP Connection between connector and bread board （ As shown in the figure above ）.

Connected to my ISP programmer after , You can use this command to check the current internal fuse configuration .

$ avrdude -patmega328p -cusbasp
...
avrdude: safemode: Fuses OK (E:FF, H:DE, L:E2)

L:E2 It's the interior we want 8mhz Set up . If your values are different , You can update it with a command like this .

/usr/bin/avrdude -patmega328p -cusbasp -Ulfuse:w:0xE2:m

And then check again .

After the internal fuse is set , You can weld the crystal . It is recommended to connect the crystal directly to the microcontroller pin , To reduce stray capacitance . Too much capacitance will make the crystal take longer to start oscillation （ Or failed to start ）.

The first 10 Step ：（ Optional ） The first step

Refer to step 1、 step 2 Or steps 3 The design schematic you selected in .

You can verify the situation so far on the bread board , Just put one LED/Resistor from D5 Connect to the ground , Then upload the firmware . If everything goes well ,LED Will flash briefly once per second ;
Next , You can add EPaper display . The data on the monitor will not be correct , But it should show some data ;
then , add to PHT modular , And verify that it works ;
And finally GPS modular .

If the test is normal , We can move everything to a more “ permanent ” On the fixture of .

The first 11 Step ： Circuit board assembly

You can choose to use perf plate , use CNC Cut the board , Or send the design to the factory for manufacturing .

Kicad Design documents can be found in schematic/ Catalog ^[9] Find . There are three hardware options （ Are shown from the back , Because this is the way you wire by hand ）.

I use my CNC Machine made ATMega328P edition . If you don't CNC Cut PCB And interested , You can try to search on the search engine "3018 PCB", You will find many videos and articles on this topic .

Gap setting 0.4 mm , But you can be narrower （ It may not be wider ）. I use Flatcam take Kicad Of Gerber The output is converted to G Code .

Relevant documents can be found in Download at the end of the article To .

The first 12 Step ： Case design

You can design any kind of look you want , We encourage you to be creative !

Here's how I made it （ All design documents can be found in Download at the end of the article To ）.

My design uses a 3D Printed support structure and two CNC parts ： A top cover and front panel . CNC components are made of wood , Because I think it looks more beautiful than plastic . I am here OpenSCAD The whole thing is designed in advance .

I use 0.2 The main structure is printed with a layer height of mm . In my 3D On the printer , Printing took 5 A little over an hour .

I use OpenSCAD Of "projection"^[10] function , Created for the top cover and front panel 2D DXF file .

I usually use a name called "Carbide Create"^[11] Free program for , Made for CNC machine tools G Code . But the panel has a 45 Degree chamfer , and Carbide Create Is a very basic program , Can't handle this problem well （ At least I Google the forums on their website , I came to this conclusion ）. So I tried a different program , be called "CamBam"^[12], It works very well .（CamBam It's not free , But it's free to use 40 Time ）

The first 13 Step ： appendix A： Clock drift correction （ Optional ）

Yours 32k/CPU Crystals are not perfect . When GPS On , It will correct the drift . But if the drift is bad or your GPS The signal is not good , You can also apply a correction to the firmware . Currently this requires building code . stay main.c At the top of the , There are some definitions that have been commented out .

// Clock drift correction
// If your clock runs too fast or too slow, then you can enable these
//#define CORRECT_CLOCK_DRIFT
// number of seconds that a second should be added or removed
//#define CLOCK_DRIFT_SECONDS_PER_CORRECT 1800
// define this if the clock is too slow, otherwise leave it commented out
//#define CLOCK_DRIFT_TOO_SLOW

You can cancel the above two #define Remarks of statements , To enable calibration .

Just cancel the CLOCK_DRIFT_TOO_SLOW Notes （ If your clock is already slow ）.

If your clock is too fast , Don't comment . The only thing to do is set up CLOCK_DRIFT_SECONDS_PER_CORRECT...

Mathematical methods

Waited about a day , Then see how much the clock has drifted . for example , You may have to wait 23 Hours . If you see the clock slow 10 second , Then your revision will be .

(3600 * 23) / 10 = 8280 second , Each correction .

#define CORRECT_CLOCK_DRIFT
#define CLOCK_DRIFT_SECONDS_PER_CORRECT 8280
#define CLOCK_DRIFT_TOO_SLOW

Non mathematical methods

Just try one like 5000 Numbers like this , And perfect the clock when you notice that it is still too fast or too slow . Or too slow ？ try 2,500. It's too fast ？ try 10,000. Keep records , And repeatedly improve to an acceptable value , Just like the number guessing game you may have played at some time .

The first 14 Step ： appendix B： cheap GPS Power control （ About BS170 N-MOSFET）

Go over Step four " cheap GPS " The power control circuit described in , The above power cut-off circuit is called "low side switch". Its advantage is that it is easier to understand , And the number of parts is small . For all that , There are still some design problems .

GPS The ground wire of is not connected to GND Connected to a , But with MOSFET Connected to a . This means from GPS To the microcontroller UART The signal will have MOSFET The pressure drop is added to it （Vds）, Increased noise sensitivity , And may cause errors .
If your microcontroller input is specified as 3.3V The maximum of , You wouldn't want to use this design （ I choose the ATMega328P There is no such restriction ）.
3.3V（ above EN Pin ） For each MOSFET It's not a very strong starting voltage .

however ,UART It's a digital signal , The difference between the ground wires is not great , So maybe it will work anyway ？ I tried , And it works very well ...... At first , But over time , I gradually found it unreliable . To understand why , Let's refer to my original choice BS170 As my N-MOSFET Characteristic curve of ^[13].

stay X The shaft 3.3V when , We will sit on the 3.0 and 4.0V Between lines . therefore , Maybe we'll get 100mA？ Maybe enough ？

The multimeter tells me ,GPS Consume 40-60mA, But I think this is an average . according to GPS Trying to do something , It just needs more current than a transistor can allow , therefore GPS Land （MOSFET Drain electrode ） The voltage will rise . This has resulted in UART error , Lowers the GPS The overall voltage of the device , and GPS Sometimes the device still works , Sometimes it will enter the reset cycle .

One solution is to use a "high side" Power circuit , Add one to it P-MOSFET To achieve this goal . See the schematic diagram above . This eliminates the problem of separate grounding , And provide a complete 5V（ The battery ） Grid voltage fluctuation , This will make it relevant P-MOSFET Fully open .

here ^[14] yes falstad A high side design example in .

At present, I have ordered one with low-end cabling PCB, So my secondary solution is to give up BS170, While using FQP30N06L Instead of . This higher current MOSFET（ Maximum 30A！） There seems to be a serious surplus , And it does , But the curve looks much better . stay 3.3V Under voltage , There are about 10A The current margin of , Than BS170 Improved 100 times , It should be enough now ; And there is no return to instability .

Reference material

[1]

falstad: http://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWcMBMcUHYMGZIA4UA2ATmIxAUgoqoQFMBaMMAKADMLiUQUAWKwvx5Ds3MNCQwELAEoUMhEIIphuyqlSGSoUCSwBOSoczVCUfHZRYAPJQnJpeIDJAeuQTiwHEACgGUWACMlfHAUPGcwRRQwJ0gWAHd5RWVBATjEo3Ss8FUoFgBzHJQEFJFIOPzDBC5hTWJooSoweFkPZT5NUTqdTSpsaGxe3WkAZ3bPIV4GnuaQNgBDABtRugMPGc6NxVENZHg4Qu2QXePsbEUNFiA

[2]

Arduino: https://www.arduino.cc/

[3]

avr-gcc Tools : https://www.pololu.com/docs/0J61/6.3

[4]

epaper project : https://github.com/mattwach/epaper_clock

[5]

firmware Catalog : https://github.com/mattwach/epaper_clock/tree/main/firmware

[6]

Makefile: https://github.com/mattwach/epaper_clock/blob/main/src/Makefile

[7]

src/gps.c: https://github.com/mattwach/epaper_clock/blob/main/src/gps.c

[8]

https://www.nongnu.org/avrdude/: https://www.nongnu.org/avrdude/

[9]

schematic/: https://github.com/mattwach/epaper_clock/tree/main/schematic

[10]

projection function : https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Using_the_2D_Subsystem#3D_to_2D_Projection

[11]

Carbide Create: https://carbide3d.com/carbidecreate/

[12]

CamBam: http://www.cambam.info/

[13]

N-MOSFET Characteristic curve of : https://www.onsemi.com/pdf/datasheet/mmbf170-d.pdf

[14]

falstad A high side design example in : http://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWcMBMcUHYMGZIA4UA2ATmIxAUgoqoQFMBaMMAKADMLiUQUAWKwvx5Ds3MNCQxIKdiEFUwGQnKFgUeELwjjJsGQCcVCpRULHlC+JBYB3OX3DrTCp9bsIzjjR-NQWAJWcvTWJlNQ0qKiFJKCgJFkMMNHATJKp1CJoWAA8QHHIiDQw8AowIXmEQAHEABQBlFgAjOTwNMC480J5ivwBzPOSMgapRSL87Qg9gtOC3YenkxQtbIxTleR4Ha36NlCmN3ArIhM5uPiiu89iweADNQWEo0UfYqJHobFe4hBYAZ3uKldeJchAoQGwAIYAG1+dBYQA

Link to the original text ：https://www.instructables.com/E-Paper-Clock/

Original author ：mattwach

First translation ：DF Maker community

For reprint, please indicate the original author and source