ARDUINO BMS

 

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TABLE OF CONTENTS

1. Introduction
2. 3D Renderings
3. Schematics
4. Arduino Code
5. Conclusion / Future changes
6. Download original files

INTRODUCTION

Now this might seem like it was a complete waste of time to try and reinvent the wheel with creating my owm custom BMS solution. You can buy them on ebay or alibaba or banggood for super cheap and it seems like a plug and play solution.

One problem I see with this, at least for me, is that I dont completely trust those cheap BMS system.  I like to buy something that is reasonable as well as trusting that it will safely protect my cells from unbalancing.  Another this is that I like to have flexibility with how I balance my cells or anything else.

Now this is where the custom arduino BMS came into play.  I’ve designed this bms to handle a 4S battery pack so upto 16.8V fully charged and 14.8V nominal.  The balance discharge current can be adjusted by simply replacing the discharge resistor with any value you wish. Just to add this does not have over current or over voltage protection..yet 🙂 I’m currently working on an add on for this so stay tuned for that future update.

Lets get started with all the cool details for this arduino bms.

3D RENDERING

Here i just wanted to show you the 3D rendering images of the final board.  The rendering was created using kicad and its pretty nice actually for an EE cad software.

The heart of this system is the atmega328P running the minicore arduino bootloader[1]. From here you have the 4 balancing passive resistors to the right of the board.  The best part of this project is that you can replace these resistors to any value you want to customize the balance current.

The one thing that this does not have is overvoltage and overcurrent protection but that will be a separate circuit later on ;).

Now we can talk about the main features below in the schematic section.

SCHEMATICS

Below are images of the full schematics for this project:

The first page of the schematic files is a hierarchy block level of the system to help understand how a lot of these subcircuits are linked together.  Below I’ll breakdown all the pages and what exactly they do.

1. Hierarchy Block:

  • This is the overview block level that links the subcircuits on the separate pages.  I normally like to design my projects this way if I have more than 2 subcircuits because its easier to see how things are working together

2. Power Supply

  • This section is just the power supply section to power the arduino.  This is a high differential buck converter.  The input voltage can go up to 36V and output down to 1.8V with an active quiescent current of only 190uA.  Now the most important part is the quiescent current because we are trying to eliminate any wasted current since this is for a battery operated system and we do not want to drain the batteries faster than needed.

3. MCU

  • The MCU page has the Atmega328P and all the corresponding IO related to it.  Im using A0-A3 to measure the batteries via a resistor divider
  • This page also includes the external reference voltage used instead of the built in 1.1V from the atmega328p. Its a 1.25V external voltage reference that has a better tolerance at a range of temperatures.

4. Balancing Circuit

  • This page has the balacing circuit which is incharge of discharging the battery cell that has a higher potentional.  The heart of this is a bidirectional N-channel mosfet that allows current to flow in both directional either during discharge or during charging.

5. Connectors

  • This page has the power pin connectors and the BMS pads that connectors to the lithium cells.

Now that we’ve gone through the schematic lets go into the second most important part and that is the arduino code.

ARDUINO CODE

Now probably the second most important part is the arduino code that will control the mosfets triggering the discharge when a preset voltage difference is hit.

#include "Adafruit_SSD1306.h"

/* Revision: A9
 * Written by: Steven Guzman
 * Date: 7/10/2018
 * Description: This is a customizable BMS system for a 4
 *              cell lithium ion pack.
 */

#include "Wire.h"
#include "avr/wdt.h"<span id="mce_SELREST_start" style="overflow:hidden;line-height:0;"></span>

#define OLED_RESET 4
Adafruit_SSD1306 display(OLED_RESET);

#define NUMFLAKES 10
#define XPOS 0
#define YPOS 1
#define DELTAY 2

//////////////////////////////////////////////
// This variable is used for checking on
// whether the OLED screen is attached or not
//////////////////////////////////////////////
int check = LOW;

//////////////////////////////////////////////
// Sampling number for analog read values.
// Will use this sample size to calculate a
// better estimation of the analog value
//////////////////////////////////////////////
int samples = 100;

//////////////////////////////////////////////
// This is the max difference that the cells
// can achieve in respect to each other
//////////////////////////////////////////////
float tol = 0.03;

//////////////////////////////////////////////
// To temporaly store analog values from the
// cell voltages to average out later with
// the number of samples taken
//////////////////////////////////////////////
float temp_cell[4];

//////////////////////////////////////////////
// Float array to store unconverted cell values
//////////////////////////////////////////////
float cell[4];

//////////////////////////////////////////////
// Variable array to store converted voltage
// values for cell measurement
//////////////////////////////////////////////
float B[4];

//////////////////////////////////////////////
// Variable array to store voltage differences
// between cells
//////////////////////////////////////////////
float diff[4];

/////////////////////////////////////////////////
// Variable used for digital output
// signals
/////////////////////////////////////////////////
int BAT[4];

/////////////////////////////////////////////////
// Variable used for storing the cell pack
/////////////////////////////////////////////////
float PACK = 0.000;

/////////////////////////////////////////////////
// Scaling factor used for converting
// the scaled down analogread values to there
// actual values from the voltage divider
/////////////////////////////////////////////////
float scale0 = 0.25;   // 10k/(30k + 10k)
float scale1 = 0.125;  // 10k/(69.8k + 10k)
float scale2 = 0.083;  // 10k/(110k + 10K)
float scale3 = 0.0625; // 10k/(150k + 10k)

#if (SSD1306_LCDHEIGHT != 32)
#error("Height incorrect, please fix Adafruit_SSD1306.h!");
#endif

void setup()
{

  Serial.begin(9600);
  analogReference(EXTERNAL); // Configure reference voltage for
                             // external 1.25V

  //////////////////////////////////////////////
  // After switching to external reference you
  // need to read a value a couple times before
  // the reference has stabalized.
  //////////////////////////////////////////////
  analogRead(A0);
  analogRead(A0);
  analogRead(A0);
  delay(20);

  // Setup up watchdog timer to reset
  // after 4 seconds
  wdt_enable(WDTO_4S);

  ///////////////////////////////////////////////
  // Variables to set the digital output
  // pins 1-4
  ///////////////////////////////////////////////
  BAT[0] = 5;
  BAT[1] = 6;
  BAT[2] = 7;
  BAT[3] = 8;

  ///////////////////////////////////////////////
  // Setting digital pins to output configuration
  ///////////////////////////////////////////////
  pinMode(BAT[0], OUTPUT);
  pinMode(BAT[1], OUTPUT);
  pinMode(BAT[2], OUTPUT);
  pinMode(BAT[3], OUTPUT);

  ///////////////////////////////////////////////
  // Sets the digital outputs to an initial low
  // state
  ///////////////////////////////////////////////

  digitalWrite(BAT[0],LOW);
  digitalWrite(BAT[1],LOW);
  digitalWrite(BAT[2],LOW);
  digitalWrite(BAT[3],LOW);

}

void loop()
{

  Wire.requestFrom(0x3C, 1); // Pings OLED screen

  ///////////////////////////////////////////////
  // If OLED pings back and check statement
  // equals 1, then initiate the OLED screen
  // and reset the check value to 0 so it will
  // not continue to re-initiate. It needs to
  // initiate another request one last time
  ///////////////////////////////////////////////
  if (Wire.available() &amp;&amp; check == HIGH )
  {
    display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
    check = 0;
    Wire.requestFrom(0x3C, 1);
  }
  if ( Wire.available() &amp;&amp; check == LOW)
  {
    // Leave blank
  }
  else if (!Wire.available())
  {
    check = 1;
  }

  ///////////////////////////////////////////////
  // Sets the temp variable array back to zero
  ///////////////////////////////////////////////
  for (int x = 0; x &lt;4; x++)
  {
    temp_cell[x] = 0.00;
    diff[x] = 0.00;
    cell[x] = 0.00;
  }
  ///////////////////////////////////////////////
  // For loop used to record battery cell voltage
  // information and used later to average out
  // the readings
  ///////////////////////////////////////////////
  delay(100);

  ////////////////////////////////////////////////
  // Using true RMS calculation for computing a
  // better average estimate for multiple samples.
  ////////////////////////////////////////////////
  for (int i = 0; i &lt; samples; i++)
  {
    temp_cell[0] = temp_cell[0] + sq((analogRead(A0)/scale0)* (1.249 / 1024));
    delay(1);
    temp_cell[1] = temp_cell[1] + sq((analogRead(A1)/scale1) * (1.249 / 1024));
    delay(1);
    temp_cell[2] = temp_cell[2] + sq((analogRead(A2)/scale2) * (1.249 / 1024));
    delay(1);
    temp_cell[3] = temp_cell[3] + sq((analogRead(A3)/scale3) * (1.249 / 1024));
    delay(1);
  }
  cell[0] = sqrt(temp_cell[0] / samples);
  cell[1] = sqrt(temp_cell[1] / samples);
  cell[2] = sqrt(temp_cell[2] / samples);
  cell[3] = sqrt(temp_cell[3] / samples);

  ////////////////////////////////////////////////
  // Scale up the cell values and then convert to
  // to voltage values
  ////////////////////////////////////////////////
  B[0] = (cell[0]);
  B[1] = ((cell[1] - cell[0]));
  B[2] = ((cell[2] - cell[1] ));
  B[3] = ((cell[3] - cell[2] ));
  PACK = B[3] + B[2] + B[1] + B[0];

  ///////////////////////////////////////////////////////////////////
  // Compares each cell voltage to each other and then finds the
  // lowest cell value.  Then it stores the difference between the
  // lowest cell and the remaining cells for comparison
  ///////////////////////////////////////////////////////////////////
  if ( (B[0] &lt;= B[1]) &amp;&amp; (B[0] &lt;= B[2]) &amp;&amp; (B[0] &lt;= B[3]))
  {
  diff[1] = B[1] - B[0];
  diff[2] = B[2] - B[0];
  diff[3] = B[3] - B[0];
  }
  else if ((B[1] &lt;= B[0]) &amp;&amp; (B[1] &lt;= B[2]) &amp;&amp; (B[1] &lt;= B[3]))
  {
  diff[0] = B[0] - B[1];
  diff[2] = B[2] - B[1];
  diff[3] = B[3] - B[1];
  }
  else if ((B[2] &lt;= B[0]) &amp;&amp; (B[2] &lt;= B[1]) &amp;&amp; (B[2] &lt;= B[3]))
  {
  diff[0] = B[0] - B[2];
  diff[1] = B[1] - B[2];
  diff[3] = B[3] - B[2];
  }
  else
  {
  diff[0] = B[0] - B[3];
  diff[1] = B[1] - B[3];
  diff[2] = B[2] - B[3];
  }

  //////////////////////////////////////////////////////////////////
  // It enables the balancing protocol for a given cell that has a
  // greater voltage difference from the lowest cell and the set
  // tolerance.
  //////////////////////////////////////////////////////////////////
  delay(1);
  for ( int x = 0; x  tol )
    {
      digitalWrite(BAT[x], HIGH);
      delay(1);
    }
    else
    {
      digitalWrite(BAT[x], LOW);
      delay(1);
    }
    delay(1);
  }

  // text display tests
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.setCursor(0,0);
  display.print(&quot;V1:&quot;);
  display.print(B[0]);
  display.println(&quot;V&quot;);
  display.print(&quot;V2:&quot;);
  display.print(B[1]);
  display.println(&quot;V&quot;);
  display.print(&quot;V3:&quot;);
  display.print(B[2]);
  display.println(&quot;V&quot;);
  display.print(&quot;V4:&quot;);
  display.print(B[3]);
  display.println(&quot;V&quot;);

  display.setCursor(70,0);
  display.print(&quot;VP:&quot;);
  display.print(PACK);
  display.print(&quot;V&quot;);

  display.setCursor(70,8);
  display.print(&quot;Config:&quot;);
  display.print(&quot;4S&quot;);
  display.display();
  delay(1);
  display.clearDisplay();
  wdt_reset();
}

Lets break down this code in order to understand my thought process behind this.arduino_code_sampling_section

  1. The samples variable is used to create an average sampling of the battery cells to eliminate any noise issues.  The averaging technique I used in this project is a little different than most but I will explain later on
  2. The next variable is the tol variable.  This variable is the maximum voltage different between the lowest cell and the rest of the cells in the 4S pack.  Currently its set to a maximum of 30mV difference but this can be set to a minimum of 10mV because of the 8-bit adc on the arduino.

arduino_code_voltage_divider_section

  1. Here is the scaling factor for the adc from the cell measurements.  We have different values because in order to get the best accuracy measuring in reference to ground, different values were needed for measuring cell 1 which has a max of 4.2V and cell 4 which measures a max of 16.8V.

arduino_code_oled_section

  1. This portion of the code is mainly for the OLED screen.  It allows for the screen to be removed and re attached without having to reset the arduino.  Before you had to initialize it in the setup but with this loop it is initialized in the main loop when it detects the screen.

arduino_code_average_section

  1. Now this section is averaging the adc values from all 4 cells to get a best measurement of the cell voltage values.  Instead of using the traditional sample 25 and take the average, I’m using a true RMS calculation that will give you a slightly better voltage measurement that just taking the average.  It will be at a closer measurement to your multimeter than using average sample.

 

CONCLUSION / ISSUES

Here is the final PCB:

I’m pretty excited to do more testing on this and I will post my technical review later on that includes current consumption, maybe a mini manual on how to use it or change values for your own build.

Again this does not include an over voltage or over current protection circuit but I decided to make that a separate board with its own controller in order to make the board as small as I could and isolate the two circuits as a redundancy.  I’m still making some tweaks and might make another revision but all in all I’m very happy about it.

Some current issues that I know off.

  1. You might have to calibrate with a known good multimeter.  The arduinos ADC has some weird issues with analogPin A2 measuring higher than the rest.  I added a calibration value in the code to help with that.

 

DOWNLOAD ORIGINAL FILES

Download here.

For the Bill of Materials, I’ve embedded the datasheets for some of the major components in case you wondered why the file is larger than it should.

 

Footnotes

1. Minicore bootloader

Electronics: FTDI USB TO UART

Donations

Anything would help really. My goal is to have this website ad free and so you can enjoy my content without having to look at ads. Thank you

$1.00

 

 

TABLE OF CONTENTS

1. Introduction
2. Bill of Materials
3. Schematic
4. Oshpark
5. Final Thoughts
6. Download Original files

INTRODUCTION

With the Arduino mini, there is a need for a USB to UART controller to upload your sketches and this could also be used for the ESP8266.

This project is inspired and based off the Sparkfun’s FT231X breakout board design.  I’ve created this project because 1. I like designing and soldering electronics 2. Try to create a cheaper alternative to the popular FT232RL and also add 1 or 2 features to the current FT231X breakout board.

BILL OF MATERIALS

For the bill of materials, its pretty straight forward.  I’ve attached links to digikey for each component as I find them easier to order from but you could also get the parts from arrow or mouser as well.

 

 

Component Description Part number Quantity Link
47pF, 0603, 50V C1608C0G1H470J080AA 2 Digikey
0.1uF, 0603, 25V CGA3E2X7R1E104K080AA 4 Digikey
10uF, 0805, 6.3V TCJN106M006R0250 1 Digikey
Micro B Connector 10118192-0001LF 1 Digikey
6-pin Header M20-7910642R 1 Digikey
N-Channel FET BSS84-FDICT-ND 1 Digikey
27 ohm, 1206 RC1206JR-0727RL 2 Digikey
10k, 0603 RT0603DRD0710KL 2 Digikey
FT231X, SSOP-20 FT231XS-U 1 Digikey

SCHEMATIC

Below I’ve attached an image of the schematic but i’ve also attached the original kicad files and a PDF version of the schematic at the end of the post.

OSHPARK

If you feel like you want to get this board made, I’ve attached a link to my oshpark project.  With oshpark, I find they make great quality boards at a great price for small sized boards.

Order from OSH Park

FINAL THOUGHTS

I know this was a short post and project but I found it important to share another option for those’s who want to find a cheaper solution and want to learn along the way.  You can find a lot cheaper solutions on amazon that are china made but i’ve read stories in some cases that they were not genuine FT232RL ICs.  If you wish to build your own, its very easy and rewarding at the same time.

In the next revision I will add LEDS for TX and RX indication as for this version I eliminated to save some cost and space.

Hope you enjoyed this post, THANK YOU 🙂

DOWNLOAD ORIGINAL FILES

https://app.box.com/s/50ap9obq89ucydbqqn54tye6ae3xiu34

 

CNC: CNC CONTROL BOX

Donations

Anything would help really. My goal is to have this website ad free and so you can enjoy my content without having to look at ads. Thank you

$1.00

 

SUMMARY

1. Introduction
2. Bill of Materials
3. Block Diagram
4. Schematics/CAD DESIGN
5. Assembly
6. Final Thoughts/ Improvements
7. Download Original Files

 

INTRODUCTION

Arduino and the implementation of GRBL has allow for amazing things to be created.  One of those things are low cost CNC machines that enable us to create anything we want.

I bought myself a low cost CNC engraver from amazon and after modifying it, it has been one of my best investments because as en electrical engineer I can create PCB boards to test my designs here at home and verify before getting them sent out. One problem I usually have is that I use my laptop to run the gcode software and my laptop is really big and sometimes a hassle to keep on my desk.

My solution was to create this project and make a standalone CNC machine controller to run the gcode software in a compact package.  I tried fiddling around with using a raspberry pi 2 as my main PC but I’m still a beginner with raspberry pi’s and I had issues getting the settings right.  My next option was to use a windows based machine and luckily I found just the solution.

In this tutorial I will explain how I put this together and what improvements could be made.

BILL OF MATERIALS

Component Quantity Link
Windows computer stick 1 Amazon
Wireless keyboard/mouse 1 Amazon
DIY HDMI male adapter angled 1 Adafruit
DIY HDMI female adapter 1 Adafruit
DIY HDMI Ribbon cable 20cm 1 Adafruit
3.5 inch Screen 1 Amazon
Left angled micro usb cable 1 Amazon
Top angled usb 3.0 extension 1 Amazon
USB Board
USB Female Connector 2 Sparkfun
5VWM TVS Diode 1 Digikey
0.1uF 50V X7R 1206 1 Digikey
1uF 25V X7R 0805 1 Digikey
10uF 16V X5R 0805 1 Digikey
100 OHM 0.1% 1/8W 0805 2 Digikey
TERM BLOCK 5MM 2POS 2 Digikey

BLOCK DIAGRAM

Visio_blog - block diagram

Here is the block diagram for how this project is wired.  With the exception of the enclosure itself and the usb power board, everything was bought ready to go.  I’ve added a fan as a just in case because the computer stick does generate some heat so the fan will prevent the system from over heating but so far it does not seem to be an issue with heat and therefore is an option.

The 5V and 12V supply are coming from my 24V power supply that powers my Arduino GRBL shield.  What I did was use two step down converters 1) For 5V step down and 2) For 12V step down.  I realized this might not be idle but it is my first revision of this project.

SCHEMATICS/ CAD DESIGN

The only schematics I have is for the USB power board and I created that using Kicad.  The board was basic, since both the screen and the windows computer stick ran on 5V via micro USB, I needed to distribute power from one source into two loads.  To add some safety, I did add a TVS 5VWM diode to prevent over voltage spikes from destroying the devices along with some filtering capacitors.

Electronics_pdf - cnc usb power board-1

If its a little blurry don’t worry because all original files will be included in a download link at the end.

Now for the enclosure, I designed it using Fusion 360.  Honestly, I am not a Mechanical engineer/Designer so this was my first attempt at designing something in a CAD software.  Mine you its really just a box but Fusion 360 makes it really easy to design for someone who had no prior experience.

I designed this in two pieces:

  1. The bottom portion of the enclosure:CAD_pdf - Enclosure Drawings-1
  2. The Lid for the enclosure:CAD_pdf - Lid Drawings-1

For material used for making this enclosure, I used my Maker Select V2 3D printer with PETG filament for the temperature resistance and flexibility.

I will include the STL files so you guys can 3D print this yourself.

ASSEMBLY

Now for the fun part, putting this thing together and hoping everything works without the magic white smoke lol jk.  This was actually very easy to put together though there were a couple of design hick ups.

Since I wanted to get the print out as fast as possible, I sacrificed quality of the print which is why it looks the way it does but its very function.

As I mentioned I did have some design issues after I was putting this thing together.  If you look at image 3, you can see that the usb power board is tilted up and thats because I placed the cooling fan to close.  The board was able to fit but I could not connect anything because the fan was blocking the connectors.

I decided to use hot glue to hold everything down because it wouldn’t be a DIY project if hot glue wasn’t involved.

In image 4, you can see I used some basic terminal block connectors to attach my 5V and 12V supply.  You can also see the USB port to connect the arduino grbl controller board.

FINAL THOUGHTS/IMPROVEMENTS

Overall I enjoyed putting this project together.  It’s made my project efficiency increase dramatically because I don’t have to take it out and set it up every time I want to make a board.

With anything we do, there’s always room for improvements.  In a future version of this project I plan to improve the way I connect my external 5V and 12V supply instead of using the terminal blocks.  I might possibly use some type of molex connector that can easily detach.  To reduce the amount of external connectors, I could switch out the 12V fan with a 5V fan and run it with only one step down converter.  I’m going to also move the fan placement so that I do not have to angle the usb power board.

DOWNLOAD ORIGINAL FILES

Bill of Materials

KiCad files

3D STL files

PDF Documents

Thank you for visiting and I hope you enjoyed this project.

Please leave a comment and let me know about your thoughts, improvements or any issues you see with this post.  All comments are welcomed 🙂

Arduino: WiFi Temperature Data Logger

Introduction

Lets build a WiFi temperature data logger!!  The reason this project came to mind was because I needed to monitor the temperature of an outside enclosure box that will eventually house a couple of lithium ion batteries.  Can’t have the box get too hot or else we will end up having a nice backyard campfire.

This temperature data logger consist of three sections:

  1. The WiFi web server
  2. The temperature sensor
  3. The sleep controller

Lets get into the project now 🙂

Schematics, PCB, Arduino Libraries can be downloaded Here

Bill of Materials

  • x1 ESP8266 – Link
  • x1 Barometric (BMP180) – Link
  • x1 Atmega328P-PU – Link
  • x1 FTDI to Serial Converter – Link
  • x1 2N7002 – Link
  • x1 DMG2305UX-7 – Link
  • x7 10k Resistor 1206 – Link
  • x3 0.1uF Capacitor 1206 – Link
  • Female Headers – Link
  • x1 28 pin DIP Socket – Link
  • x1 PCB Terminal block – Link
  • x1 3.3V Boost Converter – Link

Hardware/Schematic/Assembly

I’ve designed this project to consist of two microcontrollers.  Its not the most efficient way of doing it but it is effective.  The heart of this project is the ESP8266-ESP01 IC.  It will take in the data from the BMP180 sensor over I2C and send the data over to a web hosting site Thingspeak.com

Schematic:

Webserver - Schematic

The schematic is not that all complicated but it is very effective at trying to save as much battery as possible and deliver my data for viewing purposes.

In order to have this be powered by 2x AA batteries and last longer then a couple of days or weeks, I needed a couple of things to make this possible which is where the second microcontroller comes into play.

First, we need to make sure we have a stable power supply that can provide up to at least 0.3A and have a minimum quiescent current in the low uA range.

Thingspeak.com

Before we get started into writing the code on the ESP8266 we need to set up an account at thingspeak.

Blog - Thingspeak

Click on the signup and fill out the information:

Blog - Thingspeak_2

Click on new channel:

Blog - Thingspeak_3

The most important information to fill out is the fields, in our case we will fill out field 1 and type in temperature.  The name could be any name you want, for this purpose we will write Temperature Data Logger. Once finish, scroll down and click save.

Blog - Thingspeak_4Blog - Thingspeak_5

The final piece of information we need is the API key, for this just click on the API Keys button and copy the Write API Key.

Blog - Thingspeak_6

Now we can move on to the code.

Click here for step by step on installing the ESP8266 arduino addon.[3]

ESP8266 Code

//////////////////////////////////////////////////////////////////////////////////
// Name: Steven Guzman                                                          //
// Date: 4/4/2017                                                               //
// Description: Temperature webserver that will update every 30 minutes to      //
//              thinkspeak with data that shows the temperature of the inside   //
//              of the enclosure.                                               //
//////////////////////////////////////////////////////////////////////////////////

#include <ESP8266WiFi.h&>
#include <Wire.h>
#include <SFE_BMP180.h>

SFE_BMP180 pressure;

char status;
double t, tf;

// Replace with your channel's thingspeak API key
String apiKey = "";

// Enter your wifi information below
const char* ssid = "";
const char* password  = "";

const char* server = "api.thingspeak.com";

WiFiClient client;
void setup()
{
Serial.begin(115200);
delay(10);
// Pin 0 = SDA
// Pin 2 = SCL
Wire.begin(0,2);

WiFi.begin(ssid,password);

Serial.println();
Serial.println();
Serial.print("Connecting to ");

while (WiFi.status() != WL_CONNECTED)
{
delay(500);
Serial.print(".");
}

Serial.println("");
Serial.println("WiFi Connected");

// Initialize the sensor
if (pressure.begin())
{
Serial.println("BMP180 init success");
}
else
{
Serial.println("BMP180 init fail\n\n");
//while(1);
}

// Print the IP address
Serial.print("Use this URL to connect: ");
Serial.print("http://");
Serial.print(WiFi.localIP());
Serial.println("/");
}

void loop()
{
// This starts the BMP180 sensor and takes a reading
status = pressure.startTemperature();
if (status !=0)
{
delay(status);
status = pressure.getTemperature(t);
}
// Converts Celsius into Farenheid
tf = (9.0/5.0)*t+32.0,2;
if(client.connect(server,80))
{
char t_buffer[10];

// This will convert the double variable into a string
String temp=dtostrf(tf,0,5,t_buffer);
String postStr = apiKey;
postStr +="&field1=";
postStr += String(temp);
postStr +="\r\n\r\n";

client.print("POST /update HTTP/1.1\n");
client.print("Host: api.thingspeak.com\n");
client.print("Connection: close\n");
client.print("X-THINGSPEAKapiKey: "+apiKey+"\n");
client.print("Content-Type: application/x-www-form-urlencoded\n");
client.print("Content-Length: ");
client.print(postStr.length());
client.print("\n\n");
client.print(postStr);

Serial.print("Temperature: ");
Serial.println(t);
Serial.println((9.0/5.0)*t+32.0);
Serial.println(temp);
}

client.stop();

Serial.println("Waiting...");
delay(20000);
}

Arduino Code

///////////////////////////////////////////////////////////////////////////////////////////
/// Title:  Auto Garden Project                                                          //
/// Author: Steven Guzman                                                                //
/// Date:   4/6/17                                                                      //
/// Description: This project will automatically water a plant when the sensor reads low //
///              water levels in the soil.  If sensor reads low water, it will turn on   //
///              boost converter that controls the solenoid valve and then turn on the   //
///              solenoid valve control circuit to allow water to flow into the soil.    //
///////////////////////////////////////////////////////////////////////////////////////////

#include <LowPower.h>

int ESP1 = 2;          // Turns on sensor; set to low for battery consumption purposes (Active High)

void setup()
{

pinMode(ESP1,OUTPUT);     // Configure sensor control as output
digitalWrite(ESP1,LOW);   // Setup as low output
delay(100);
}

void loop()
{

digitalWrite(ESP1,HIGH);  // Turns on the ESP8266
delay(15000);             // 15 second delay
digitalWrite(ESP1,LOW);   // Turns off the ESP8266

// Loops the 8 second internal to extend the sleep state
// 15 = 2 minutes
// 37 = 5 minutes
// 75 = 10 minutes
// 112 = 15 minutes
// 255 = 30 minutes

for(int x = 0; x <= 255; x++)
{
LowPower.powerDown(SLEEP_8S,ADC_OFF,BOD_OFF);
}

}

Programming

ESP8266-ESP01

First things first, we will upload the code to the ESP8266-ESP01.  This one is a little bit tricky but after awhile you’ll get the hang of it.

You need to make sure your settings are correct under the Arduino IDE.

See image below:

Arduino ESP8266 settings

Here’s the wiring diagram for connecting the FTDI programmer to the ESP8266:

Blog - ESP8266_WIRING

Now that your settings are correct, this is were it gets a little tricky to upload the code, you need to follow the steps below in order to upload correctly and successfully

Before hitting upload:

  1. Ground GPIO0 (hold down the push button JP2)
  2. Reset by pulling RST pin to ground (Press and release JP1 button)
  3. Once it restarts, hit the upload sketch icon
  4. When you see compiling sketch switch to uploading, then release the GPIO0 pin
  5. uploading should begin
ATMEGA328P-PU (ARDUINO LILYPAD)

Next, we will upload the second code into the ATmega328 which has the lilypad bootloader installed ( Click HERE [2] for tutorial on flashing ATMEGA328P-PU with bootloader).

See image below for settings:

Blog - ESP8266

Final Thoughts and Future updates

And now the final product:

Blog - Thingspeak_graph

Its not the most elegant but I actually used my CNC machine to make these boards, in the future I might get them professionally made but for now its perfect for me.

Future Updates:

  1. Replace the ATMEGA328P-PU IC with a smaller ATTINY85 which can also be flashed with the Arduino bootloader
  2. Connect the Arduino to the I2C communication lines to expand its data logging capability
  3. Since this is running on 2x AA NiMH batteries, it would be great to monitor battery capacity.  We can use one of the analog pins on the arduino to read the data and send it over I2C to the ESP8266

1. Arduinesp
2. ATMEGA328 Bootloader
3. ESP8266 installation

Boost Converter – 3.3V@ 0.4A

Its time to show you my 3.3V output boost Converter design. In one of my earlier post I showed you step by step on how to design your own boost converter and if you haven’t read that yet then click here.

You can purchase this board fully assembled by clicking here. 🙂

Lets get started:

Intro.

First of all, why do we even need this converter? Well every sensor, microcontroller, arduino, ESP8266, and various other digital components need a constant voltage.  A constant voltage is necessary to maintain proper operation of these components.

Here we will see the advantage of this boost converter.

Specifications.

Below are the operating specs for this converter

\Huge \bold V_\text{IN} = 1.8V - 2.4V

\Huge \bold V_\text{OUT} = 3.3V 

\Huge \bold I_\text{OUT} = 0.4A 

  • Note: Different Vin voltages gives you different max power output
    • \Huge \bold V_\text{IN} = 1.8V @ I_\text{OUT}: 0.2A
    • \Huge \bold V_\text{IN}: 2.0V @ Iout: 0.3A
    • \Huge \bold V_\text{IN}: 2.4V @ Iout: 0.4A

\Huge \bold V_\text{P-P} = 80mV 

Bill of Materials.

Here is a screenshot of the bill of materials.  I added the suppliers on the spreadsheet because I’ve found that some sites have better pricing than others.

Using octopart.com, you can actually find the best value for the component you’re looking for.  I highly suggest you go look at the site.

BOM - L6920

Schematic.

Attached here is the schematic for this project.  All the original files are available for download at the bottom of the page.

L6920.Rev.5

Layout.

I figure I’d help you guys out a bit if I added the layout for this board.  My approach for this layout was to minimize the overall size in order to get a better price for manufacturing the board.

L6920.PCB.Rev.5

Testing.

Here comes the fun part, actually testing what you designed.  Now one thing that took me awhile to learn was that design and theory never really match reality.  There are a lot of different parameters that are not accounted for when designing in theory.

A couple of the major issues that could make or break your design is parasitic elements.  One of the biggest parasitic elements is ESR for output capacitors.  This is the equivalent series resistance of the capacitor that is not taking into account when designing.  In my post that covers the design of a boost converter, I emphasizes this topic to make you aware of this parasitic element.

Now, my design parameters consisted of loading the converter at 3 different voltage inputs (1.8V, 2.0V, and 2.4V).  Each input voltage was loaded starting at 0.1A and ending at 0.4A.  This load all depended on which input voltage was tested because the lower input voltage cannot provide the max output power.

First test – Vin: 1.8V @ 0.2A

Will add soon.

Next test – Vin: 2.0V @ 0.3A

2.0V_0.3A_3.13.17

Last test – Vin: 2.4V @ 0.4A

2.4V_0.4A_3.13.17

After completely the voltage ripple test, I also conducted a load regulation test at max load for each input voltage.  I got a 1.5% voltage drop from calculated voltage meaning at full load, my output voltage was 3.25V at the lowest.

Downloads.

Order from OSH Park

All files available here – Click

How-to: Design a Boost Converter

image-boost-converter
Figure 1: Basic Boost Converter Circuit

Designing a boost converter sounds complicated and intimidating, well that was always my impression when it came to this topic in school.  In reality, the design and testing of a boost converter is a lot easier than meets the eye.

Here I will walk you step by step on designing your first boost converter and how the datasheet is your best friend when designing.  For this tutorial we will be using the L6920DC IC Boost converter from skyworks.[1]

Download the Boost Converter excel spredsheet from the Resources page.

This information was referenced from TI reference report.[2]

First and foremost, download the highlighted datasheet, datasheet-l6920dc. This has all the highlighted paremeters that you will need when designing a boost converter.

Step 1:

You need to decide what are your specifications.  These are the key parameters:

  • Vin(min)
  • Vin(max)
  • Vout
  • Iout
  • n = efficiency; Most boost converters average around 85 to 90% under medium load and up to 95% on heavy load.  We will use the lowest percentage to be safe.

Example:

  • Vin(min): 1.8V
  • Vin(max): 2.4V
  • Vout: 3.3V
  • Iout: 0.4A
  • n = 87% or 0.87

Step 2:

With your specifications, next step is to find your DUTY CYCLE:

\bf \Huge D= 1 - \cfrac{(V_{\text{IN}}*n)}{V_{\text{OUT}}}

We calculated the duty cycle for both lowest input voltage and highest input voltage.

  • Lowest input voltage gives you the highest switching current you will see
  • Highest input voltage gives you the highest output current your converter can produce

Example:

\bf \Huge V_{\text{IN-MIN}}

\Huge D = 1 - \cfrac{1.8V*0.85}{3.3V} = 0.52

\bf \Huge V_{\text{IN-MAX}}

\Huge D = 1 - \cfrac{2.4V*0.85}{3.3V} = 0.36

Step 3:

Next we will estimate the switching current or CURRENT RIPPLE of the Inductor:

ΔIL = (0.3) * I_\text{OUTmax} * \cfrac{(V_\text{OUT})}{(V_\text{IN})}

Example:

\bf \Huge V_{\text{IN-MIN}}

ΔIL = \Huge  (0.3) * 0.4A * \cfrac{3.3V}{1.8V} = 0.22A

\bf \Huge V_{\text{IN-MAX}}

ΔIL = \Huge  (0.3) * 0.4A * \cfrac{3.3V}{2.4V} = 0.165A

Step 4:

Next we calculate the minimum INDUCTANCE we need:

\bf \Huge L_\text{MIN} = \cfrac{(V_\text{IN})*(V_\text{OUT} - V_\text{IN})}{\Delta I_\text{L}*f_\text{S}*V_\text{OUT}}

\bf \Huge f_\text{S} – This is the switching frequency that the converter will operate at.

Example:

\bf \Huge V_{\text{IN-MIN}}

\Huge L_\text{MIN} = \cfrac{(1.8V)*(3.3V - 1.8V)}{0.22A*1MHz*3.3V} = 3.72uH

\bf \Huge V_{\text{IN-MAX}}

\Huge L_\text{MIN} = \cfrac{(2.4V)*(3.3V - 2.4V)}{0.165A*1MHz*3.3V} = 3.97uH

We would select the highest inductance value to meet our input voltage rage of 1.8V-2.4V

When selecting the inductor, the key parameters you need to look for is low DCR, package size, and max current the inductor can handle.

DCR – Is the resistance in the coil because at the end of the day, an inductor is still a wire. When you keep this value at a minimum, it will increase your effieciency and the ability to provide a higher output power.

In step 7 , you will calculate the maximum current the inductor will see and there you will have all the necessary parameters needed to chose the inductor.

Step 5:

Now that we have our inductor value, we can calculate the actual CURRENT RIPPLE of the Inductor:

ΔIL = \bf \Huge \cfrac{V_{IN}*D}{f_\text{S}*L}

Example:

\bf \Huge V_{\text{IN-MIN}}

ΔIL = \Huge \cfrac{1.8V*0.525}{1MHz*3.72uH} = 0.19A

\bf \Huge V_{\text{IN-MAX}}

ΔIL = \Huge \cfrac{2.4V*0.36}{1MHz*3.97uH} = 0.18A

Step 6:

Next we need to calculate the MAX OUTPUT CURRENT the boost converter can output:

\bf \Huge I_\text{MAXOUT} = \bf  \Huge (I_\text{LIM} - \cfrac{\Delta I_\text{L}}{2}) * (1 - D)

I_\text{LIM} – This is the current switch limit of the boost converter.

Example:

\bf \Huge V_{\text{IN-MIN}}

\Huge I_\text{MAXOUT} = \bf  \Huge (0.8A - \cfrac{0.19A}{2}) * (1 - 0.52) = 0.33A

\bf \Huge V_{\text{IN-MAX}}

\Huge I_\text{MAXOUT} = \bf  \Huge (0.8A - \cfrac{0.18A}{2}) * (1 - 0.36) = 0.45A

Step 7:

Next we will calculate the MAX SWITCHING CURRENT, I_\text{SW} the Inductor will see.  This value cannot exceed the ILIM value of the boost converter:

\bf \Huge I_\text{SW-MAX} = \cfrac{\Delta I_\text{L}}{2} + \cfrac{I_\text{OUT}}{1 - D}

Example:

\bf \Huge V_{\text{IN-MIN}}

\Huge I_\text{SW-MAX} =  \cfrac{0.19A}{2} + \cfrac{0.4A}{1 - 0.525} = 0.94A

\bf \Huge V_{\text{IN-MAX}}

\Huge I_\text{SW-MIN} =  \cfrac{0.18A}{2} + \cfrac{0.4A}{1 - 0.36} = 0.72A

Note: \Huge I_\text{SW-MAX} value cannot exceed \Huge I_\text{LIM} which can be found in the datasheet.  In this example we see that with a low input voltage, the switching current exceeds the limit in the datasheet.  The boost converter might still be able to output the desired current at that low input voltage because \Huge I_\text{LIM} is the minimum switching current it can handle.  But better to be safe than sorry.

Here you can see the inductor will see a max of 0.94A at its lowest input voltage. Now we can chose the inductor for our design.

For this design I went with,MSS5131-472MLB, a 4.7uH inductor from coilcraft.[3]

Since I chose an inductor that has a higher value than previous calculated, the inductor current ripple and output power will be slightly lower but it will not effect your design negatively.

Step 8:

This step is only if your boost converter has an adjustable output voltage.

(This boost converter is a fixed output and does not require these resistors.  Step 8 values are dummy values but the process )

Here we will find R1 AND R2 values for the feedback network:

\bf \Huge I_\text{R0.5} >= 100 * I_\text{FB}

\bf \Huge I_\text{FB} – This is the current that the feedback resistor draws.

\bf \Huge R_2 = \cfrac{V_\text{FB}}{I_\text{R0.5}}

\bf \Huge V_\text{FB} – This is the feedback reference voltage

\bf \Huge R_1 =  R_2 * (\cfrac{V_\text{OUT}}{V_\text{FB}}-1)

Example:

\Huge I_\text{R0.5} >= 100 * 350nA = 35mA

\Huge R_2 = \cfrac{1.24V}{35mA} = 35.4kΩ

\Huge R_1 =  35.4k \Omega * (\cfrac{3.3V}{1.24V}-1) = 58.74kΩ

Step 9:

Next l, we will calculate the INPUT CAPACITOR and OUTPUT CAPACITOR needed to minimize the ripple going in and out of the system:

First, you find your input capacitor:

\bf \Huge C_\text{IN}: Typically this value is 4.7uF to 10uF

Next, we need to first to look at these two equations below[6]:

\bf \Huge \Delta V_\text{OUT}= \cfrac{I_\text{OUT} *T_\text{ONmax}}{ C_\text{OUT}}

\bf \Huge T_\text{ONmax} – This is the maximum on time of the boost converter.  It is also written as

\bf \Huge D * T_\text{S}

Were \bf \Huge T_\text{S} = \cfrac{1}{f_\text{S}}

\bf \Huge \Delta V_\text{OUTesr} = ESR* I_\text{SW-MAX}

ESR – All capacitors are not ideal capacitors and therefore have what is known as Equivalent Series Resistance. This is an important parameter that you need to consider when choosing the right output capacitor.

Example:

Cin = 10uF

First, we need to choose a voltage ripple that we can live with. Here I chose 50mV, and if we rearrange the first equation, we get:

 \Huge \Delta C_\text{OUTmin}= \cfrac{0.4 *6.25us}{50mV} = 50uF

Now we have a couple of options to choose from when it comes to materials for capacitors.

Most common are ceramic and electrolytic capacitors.  Each have there own pro and con.

Ceramic capacitors offer lower ESR for lower ripple but they typically do not have the bulk capacitance.

Electrolytic capacitors have bulk capacitance but generally have a high ESR that adds to ripple.

In this case I decided to go with both, getting the benefit of bulk capacitance and low ESR.

I went with a 1206 package, 10uF ceramic capacitor and a 47uF Electrolytic in parallel. For the electrolytic, they also have an aluminum polymer that has high capacitance with the added benefit of low ESR. I went with a 47uF that has an ESR of 40mΩ.

Now we plug in the values we got back into the equations and we get:Special Note: For ceramic capacitors, you need to be careful of which class and package size you choose because you only see a certain percentage of your nominal value (ex. 1206 10uF X7R will see 73% of 10uF)[4]. Click here for more info. I generally go with 1206 or 1210 with capacitors.

\Huge \Delta V_\text{OUT}= \cfrac{0.4A * 6.25us}{50uF} = 50mV

\Huge \Delta V_\text{OUTesr} = 40m\Omega*0.94A = 37mV

\Huge \Delta V_\text{OUT} = 87mV
Always refer to the datasheet and compare recommended value vs calculated[1]

You’ve now designed your own boost converter regulator.  See it wasnt too hard :).

I will post this project soon that has the schematic and bill of materials, it’ll be under the projects menu bar, stay tuned!!

Feel free to comment below and correct me if anything seems incorrect to you.

References:

1. L6920 Datasheet

2. TI Basic Calculations of a Boost Converter Power Stage

3. Coilcraft Inductor

4. Temperature and Voltage Variation of Ceramic Capacitors

5. Ceramic or electrolytic output capacitors
in DC/DC converters—Why not both?

6. Boost Converter Output Capacitor Selection