How to Run Arduino Code on 8 PIN ATTiny Microcontroller - Program ATTiny using Arduino UNO

In previous post we've seen how to shrink Arduino Projects by using ATtiny MCU instead of Arduino UNO board.

What's it all about?
In many cases, you need to run Arduino code on smaller devices. You have that large Arduino UNO Board that costs about $14 but you need to use only one or two pins to control something simple as a relay or an LED.

Then why wasting your precious Arduino board you can use for development and research on that simple project?

Instead, you can use that cheaper ATTiny Microcontroller with the same performance.

This can be both cost and size effective solution. And also you saved your beloved Arduino UNO board for more projects to try.

In this post, we'll see how to simply program ATTiny Microcontroller using Arduino UNO board.

Program ATTiny using Arduino UNO
This setup can be used to program any ATTiny Microcontroller ( ATTiny45 or ATTiny85 ).



Components:

- Arduino
- Breadboard
- ATtiny85 (or ATtiny45)
- 10uF electrolytic capacitor
- 220ohm 1/4 watt resistor
- LED

- hookup wire


Circuit Connection:

Connect the Arduino to the ATtiny as follows:

Arduino +5V      ---  ATtiny Pin 8
Arduino Ground ---  ATtiny Pin 4
Arduino Pin 10   ---  ATtiny Pin 1
Arduino Pin 11   ---  ATtiny Pin 5
Arduino Pin 12   ---  ATtiny Pin 6

Arduino Pin 13   ---  ATtiny Pin 7

Prepare the Programmer:

In this step, you start by programming Arduino UNO with code to set it as an ISP programmer.

ATTiny Core Files:

Download files from here
http://hlt.media.mit.edu/?p=1229

Code Upload:

Test:

Conclusion:

And that's concludes this simple circtiut that can be used to program ATTiny using Arduino UNO to run Arduino Code.
Thank you for reading.

Reference:

https://www.instructables.com/id/Program-an-ATtiny-with-Arduino/

New Job Opening at AVELabs - Automotive Software Company in Egypt is now hiring

It's been a long time since we announced a new vacancy on our blog.

Today we proudly announce that AVELabs is hiring

This post is copied from AVELabs page on Facebook:

Avelabs is hiring!

"Back End Software Engineer [BEND-ENG]"

*Job Description:

- Be an active member of the team behind Yonohub (yonohub.com), the first cloud-based system for designing, sharing, and evaluating autonomous vehicle algorithms using just blocks!.
- Design, develop, and test the server-side software components of Yonohub.
- Maintain and improve existing web services.
- Evaluate the technical tradeoffs of every decision.
- Build robust, lasting, and scalable services.
- Iterate quickly without compromising quality.

*Job Requirements:

- Bachelor’s degree in computer engineering, computer science, or a related field.
- Several years of experience in back end web development using Python.
- Hands-on experience developing RESTful microservices and using Docker.
- Experience deploying Python web apps in Gunicorn and uWSGI.
- Strong knowledge of Nginx.
- Strong skills in object-oriented programming, database design, SQL, and caching.
- Knowledge of MongoDB, PostgreSQL, Redis, Kubernetes, AWS highly preferred.
- Experience in C++ highly preferred, but not required.
- Excellent command of English (written and spoken).
- Excellent attitude.

>>To apply, please fill the following form (https://form.jotformeu.com/61532954063354) and select the job with the code [BEND-ENG].

How I Made a Virtual Oscilloscope and Won 1000$ on a Worldwide Contest

Yes. This is an old memory, but remembering good old memories can be a positive act to keep you fresh and motivated.

Here is my story of how I managed to win a prize on a worldwide design contest from Renesas.

At the year of 2008 , I found an advertisement in Appliance magazine about a free kit from a Microcontroller company called Renesas.

I really wanted to get this development kit. It was dedicated to motor control. I registered for this kit but unfortunately it was available only in USA and Canada.

However, my email was added in the company's clients database. Next, the company started a design contest at the same year called Renesas HTS Design Contest 2008.

The company invited me to participate in this design contest. It was a world wide contest which included shipment of free development kit to each eligible participant.

First I was admired by the idea itself of receiving a free development kit for the contest. I wanted to have this kit to learn more about Embedded C programming and to learn the Renesas technology which was new to me until that time.

To be eligible to receive the kit, there was a short demo for the company's other educational boards over a Virtual Lab environment. Then you are asked few questions to qualify for receiving the kit.

I passed through the stages of qualification and waited to receive the kit. When I received it I started to develop my design right away.

The company made a very good idea for improving the challenge through the launch of a forum for the challenge.

Each participant posted the idea of his entry and provided some technical details about it . This idea was very helpful and motivational. Any visitor or another participant can see your posted details and get admired with it or comment on it.

My design was a Multichannel Oscilloscope. The idea was very simple. I made the analog signals read by the analog-to-digital converter of the Microcontroller M16C ( on which the board is based )

The M16C has many A/D inputs but and there were 3 of them available in the challenge board.

The signals values were converted into digital in the Microcontroller and they were sent to a PC based client software which incorporated the display of a virtual Multichannel Oscilloscope.

Brief:

This project is a simple implementation of a 3 input channel oscilloscope. The Neutrino development kit has 3 available A/D inputs (including the photo-resistor).

Description:

The A/D inputs are used as analog signals input port; they are converted into the M16C microcontroller in the AD repeat mode. The host PC then reads the digitized number in the three registers of the each AD channel. The host draws the signals on the virtual oscilloscope interface.

Hardware:

The three A/D inputs are:

1- AN1 ( connected to the photo resistor )

2- AN4 ( connected to the kit ‘s I/O connector )

3- AN5 ( connected to the kit ‘s I/O connector )

The Kit I received form Renesas had i/o ports and some of them are analog input.

You can buy another Renesas Development kit from eBay.

I connected pin headers to the analog input ports.

Firmware:

Addresses of the three registers that contain digitized signals are

AN1 3C2h 962

AN4 3C8h 968

AN5 3CAh 970

Here is part of Firmware code:

Description: Initialization of a AD converter on AN1

*****************************************************************************/

void InitAD( void )

{

// adcon0 = 0x09; /* sw trigger, repeat mode, AN1 */ 

// adcon1 = 0x20; /* vref connected, 8 bit mode */

// adcon2 = 0x01; /* P10 group, sample and hold */

adcon0 = 0x09; /* sw trigger, repeat mode, AN1 */ 

adcon1 = 0x20; /* vref connected, 8 bit mode */

adcon2 = 0x01; /* P10 group, sample and hold */

adst = 1; /* start conversion */

}

Software:

The host PC runs a VB express program which read from the mentioned addresses on the user selection of the desired input port and handles this input data to a virtual oscilloscope class which draws the signal in real-time.

The user selects the input channel by a radio box. The result is loading the analog-to-digital control register 0 (adcon0 Address 982) with one of a three inputs according to the desired input port:

AN1 49h

AN4 4Ch

AN5 4Dh

From the PC based client, the user can choose the input channel to be displayed on the virtual oscilloscope and the rate at which it is displayed.

Here is part of Visual Basic.net code ( Running on PC )

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click

If Button2.Text = "Run" Then

Button2.Text = "Stop"

Button1.Enabled = False

Button4.Enabled = False

Dim D1(2) As Double

' Dim Db As Double

Dim i As Integer

ScopeStarted = True

D1(0) = 0

Do

''''''''''''''''''''''''''''''''''''''''''''

hts.GetMemory2(lBegin, lEnd, lDisplayWidth, vMemData)

outValue = vMemData.GetValue(0)

D1(0) = outValue * 0.01953125

TextBox1.Text = outValue

TextBox2.Text = D1(0)

''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

For i = 0 To 10000 Step 1

'Call ExternalNext(scopehandle, Db)

Call ShowNext(scopehandle, D1(0))

Next i

Loop Until (Not ScopeStarted)

Else

Button2.Text = "Run"

Button1.Enabled = True

Button4.Enabled = True

ScopeStarted = False

End If

End Sub

Before the last day of the deadline of the contest I submitted the source code for the Microcontroller side (written in Embedded C ) and the source code of the PC client (written in Visual Basic.Net) .

The results of the contest were announced on Renesas DevCon 2008.

I've got the 4th honorable mention prize for my entry "Multichannel Oscilloscope".

This contest was very challenging and rewarding. Thanks to Renesas who has helped me through all this contest.

Location for the HTS 2008 projects:

http://renesasrulz.com/design_contest_archives/renesas_2008_hew_target_server_design_contest/m/mediagallery/276.aspx

How to Connect Arduino UNO to USB Keyboard - The Full Length Story

The actual sit and write is the essence of being a writer. Just as in any other discipline, if you do not invest time, mind and effort in doing it, you are treating it to be just a hobby.

The mind you give to the process of writing comes back to you in a form of the Flow. The process of effortlessly create something valuable with ease and timelessness. It’s well known that whatever habit that you devote yourself to is what you can be finally rewarded for.

That's why I've wanted to make this project to concentrate on the process of writing itself.


Today I’m showing you how I’ve made this new project. Of course, it’s about Arduino and it’s about writing.

For some reason I wanted to connect Arduino to my keyboard.

Because I love writing on the keyboard.

It’s that real physical feeling of switches on my fingertips that makes me feeling creative and alive.

But there’s only a small problem. My favorite keyboard is happened to be a USB keyboard.

Yes that’s the new modern technology is about and it’s something I should be happy with.

 

But the only problem I was having when I wanted to connect my keyboard to Arduino (as a host to my keyboard) I found that the standard use of Arduino with a keyboard is the PS/2 connection.

Actually there is a good well written Arduino library for this purpose.

So how could I connect my USB keyboard to Arduino? I only remembered back then when I was looking for a keyboard for my notebook (which had no PS/2 ports in it) is that I wanted to figure out some way to use a PS/2 keyboard with a USB port but I couldn’t found this.

And that’s why I bought the USB keyboard for the first place.

But this search has helped me a lot these days when I wanted to connect my USB keyboard to Arduino.

 

  I only then remembered that although I couldn’t use a normal PS/2 keyboard with a USB port in a notebook because of the different protocol, but the opposite is doable.

I remembered that I’ve found an instructable that described building a USB to PS/2 converter.

The writer mentioned that he has tried it and it worked.

This means that you can use a modern USB keyboard with your old PCs and laptops using only this converter.

It’s just a physical converter for the connection between the keyboard and the host port(not a voltage or protocol converter). That’s because the USB keyboard can be powered from the old PS/2 port, take the CLOCK signal from it and then send DATA signal to it.

And the writer has tried to make this setup and it worked. Now it was my turn. When I looked for some information to connect a USB to an Arduino board I found that in order to do this I need either an Arduino USB shield or an Arduino board with Microcontroller that have the native USB host physical feature. Neither option were available to me.

So I’ve decided to try the physical USB to PS/2 converter - the writer has tried with his PC - between my USB keyboard and Arduino. You know what? This one also worked.

Using the PS/2 Arduino library we can connect the USB keyboard directly to Arduino boards such as Arduino UNO or Arduino Mini.

I had that female USB connector but I had to first test its pin-out with a voltmeter.

Then I made a cross connection between the USB connector and the PS/2 keyboard of the library.

USB Keyboard PS/2 Port

+5 v Vcc +5 v Vcc

Data- Data

Data+ Clock

GND GND

Components

Arduino UNO 

Female USB port

Connection

USB Port Arduino

+5 v Vcc +5 v Vcc

Data- PIN 2

Data+ PIN 3

GND GND

Software
Download and save the latest Arduino PS/2 library from here.

Open Arduino IDE.

On the sketch menu, select library. Add Zip file.

Point to the Arduino PS/2 library Zip file location and then press Enter.

On the File menu select examples.

From PS2keyboard sub-menu select International.

You find the international.ino sketch loaded into the Arduino IDE.

https://github.com/PaulStoffregen/PS2Keyboard

Edit these two lines of code

#include

const int DataPin = 8 ;

const int IRQpin = 5 ;

In this case, I used

DataPin to be Arduino Pin 2

and

IRQpin to be Arduino Pin 3

Open the Serial Monitor and watch try the keyboard as you wish.

Note:

There will be a different response from some keys on the keyboard.

This is caused by difference of Arduino response to the keyboard than the standard PC.

 

ATmega Hub Motor controller for Electric Bike

In this post I'll show you how this author used ATmega to control the HUB Motor for his electric bike.

Parts:

Schematics:

Circuit:

Source:

https://www.instructables.com/id/DC-Motor-Controller-for-Electric-Bicycle/

Check our books on Amazon:

Learn By Making: Embedded Systems Tutorial for Students and Beginners

Embedded Systems, Electronics: My Projects Collection From Instructables

DIY Arduino Quadcopter - Open Source Arduino Controlled Quadcopter

In this post we'll see how this guy has managed to build an Arduino controlled Quadcopter that successfully flied.

This Quadcopter is built around the DJI 450 Quadcopter frame and controlled using Arduino Nano and MPU-6050 Gyroscope Accelerometer unit.

Software is tailored upon the MultiWii Flight Controller code.


Schematics:

Arduino Nano

MPU-6050 Accelerometer Gyroscope Unit

Code: 

#include "Arduino.h"
#include "config.h"
#include "def.h"
#include "types.h"
#include "GPS.h"
#include "Serial.h"
#include "Sensors.h"
#include "MultiWii.h"
#include "EEPROM.h"
#include 

#if GPS

//Function prototypes for other GPS functions
//These perhaps could go to the gps.h file, however these are local to the gps.cpp  
static void GPS_bearing(int32_t* lat1, int32_t* lon1, int32_t* lat2, int32_t* lon2, int32_t* bearing);
static void GPS_distance_cm(int32_t* lat1, int32_t* lon1, int32_t* lat2, int32_t* lon2,uint32_t* dist);
static void GPS_calc_velocity(void);
static void GPS_calc_location_error( int32_t* target_lat, int32_t* target_lng, int32_t* gps_lat, int32_t* gps_lng );
static void GPS_calc_poshold(void);
static uint16_t GPS_calc_desired_speed(uint16_t max_speed, bool _slow);
static void GPS_calc_nav_rate(uint16_t max_speed);
int32_t wrap_18000(int32_t ang);
static bool check_missed_wp(void);
void GPS_calc_longitude_scaling(int32_t lat);
static void GPS_update_crosstrack(void);
int32_t wrap_36000(int32_t ang);


// Leadig filter - TODO: rewrite to normal C instead of C++

// Set up gps lag
#if defined(UBLOX) || defined (MTK_BINARY19)
#define GPS_LAG 0.5f                          //UBLOX GPS has a smaller lag than MTK and other
#else
#define GPS_LAG 1.0f                          //We assumes that MTK GPS has a 1 sec lag
#endif  

static int32_t  GPS_coord_lead[2];              // Lead filtered gps coordinates

class LeadFilter {
public:
    LeadFilter() :
        _last_velocity(0) {
    }

    // setup min and max radio values in CLI
    int32_t         get_position(int32_t pos, int16_t vel, float lag_in_seconds = 1.0);
    void            clear() { _last_velocity = 0; }

private:
    int16_t         _last_velocity;

};

int32_t LeadFilter::get_position(int32_t pos, int16_t vel, float lag_in_seconds)
{
    int16_t accel_contribution = (vel - _last_velocity) * lag_in_seconds * lag_in_seconds;
    int16_t vel_contribution = vel * lag_in_seconds;

    // store velocity for next iteration
    _last_velocity = vel;

    return pos + vel_contribution + accel_contribution;
}


LeadFilter xLeadFilter;      // Long GPS lag filter 
LeadFilter yLeadFilter;      // Lat  GPS lag filter 

typedef struct PID_PARAM_ {
  float kP;
  float kI;
  float kD;
  float Imax;
  } PID_PARAM;
  
PID_PARAM posholdPID_PARAM;
PID_PARAM poshold_ratePID_PARAM;
PID_PARAM navPID_PARAM;

typedef struct PID_ {
  float   integrator; // integrator value
  int32_t last_input; // last input for derivative
  float   lastderivative; // last derivative for low-pass filter
  float   output;
  float   derivative;
} PID;
PID posholdPID[2];
PID poshold_ratePID[2];
PID navPID[2];

int32_t get_P(int32_t error, struct PID_PARAM_* pid) {
  return (float)error * pid->kP;
}

int32_t get_I(int32_t error, float* dt, struct PID_* pid, struct PID_PARAM_* pid_param) {
  pid->integrator += ((float)error * pid_param->kI) * *dt;
  pid->integrator = constrain(pid->integrator,-pid_param->Imax,pid_param->Imax);
  return pid->integrator;
}
  
int32_t get_D(int32_t input, float* dt, struct PID_* pid, struct PID_PARAM_* pid_param) { // dt in milliseconds
  pid->derivative = (input - pid->last_input) / *dt;

  /// Low pass filter cut frequency for derivative calculation.
  float filter = 7.9577e-3; // Set to  "1 / ( 2 * PI * f_cut )";
  // Examples for _filter:
  // f_cut = 10 Hz -> _filter = 15.9155e-3
  // f_cut = 15 Hz -> _filter = 10.6103e-3
  // f_cut = 20 Hz -> _filter =  7.9577e-3
  // f_cut = 25 Hz -> _filter =  6.3662e-3
  // f_cut = 30 Hz -> _filter =  5.3052e-3

  // discrete low pass filter, cuts out the
  // high frequency noise that can drive the controller crazy
  pid->derivative = pid->lastderivative + (*dt / ( filter + *dt)) * (pid->derivative - pid->lastderivative);
  // update state
  pid->last_input = input;
  pid->lastderivative    = pid->derivative;
  // add in derivative component
  return pid_param->kD * pid->derivative;
}

void reset_PID(struct PID_* pid) {
  pid->integrator = 0;
  pid->last_input = 0;
  pid->lastderivative = 0;
}

#define _X 1
#define _Y 0

#define RADX100                    0.000174532925  

uint8_t land_detect;                 //Detect land (extern)
static uint32_t land_settle_timer;
uint8_t GPS_Frame;            // a valid GPS_Frame was detected, and data is ready for nav computation

static float  dTnav;            // Delta Time in milliseconds for navigation computations, updated with every good GPS read
static int16_t actual_speed[2] = {0,0};
static float GPS_scaleLonDown; // this is used to offset the shrinking longitude as we go towards the poles

// The difference between the desired rate of travel and the actual rate of travel
// updated after GPS read - 5-10hz
static int16_t rate_error[2];
static int32_t error[2];

static int32_t GPS_WP[2];   //Currently used WP
static int32_t GPS_FROM[2]; //the pervious waypoint for precise track following
int32_t target_bearing;     // This is the angle from the copter to the "next_WP" location in degrees * 100
static int32_t original_target_bearing;  // deg * 100, The original angle to the next_WP when the next_WP was set, Also used to check when we pass a WP
static int16_t crosstrack_error;     // The amount of angle correction applied to target_bearing to bring the copter back on its optimum path
uint32_t wp_distance;                // distance between plane and next_WP in cm
static uint16_t waypoint_speed_gov;  // used for slow speed wind up when start navigation;


////////////////////////////////////////////////////////////////////////////////////
// moving average filter variables
//

#define GPS_FILTER_VECTOR_LENGTH 5

static uint8_t GPS_filter_index = 0;
static int32_t GPS_filter[2][GPS_FILTER_VECTOR_LENGTH];
static int32_t GPS_filter_sum[2];
static int32_t GPS_read[2];
static int32_t GPS_filtered[2];
static int32_t GPS_degree[2];    //the lat lon degree without any decimals (lat/10 000 000)
static uint16_t fraction3[2];

static int16_t nav_takeoff_bearing;  // saves the bearing at takeof (1deg = 1) used to rotate to takeoff direction when arrives at home



//Main navigation processor and state engine
// TODO: add proceesing states to ease processing burden 
uint8_t GPS_Compute(void) {
  unsigned char axis;
  uint32_t dist;        //temp variable to store dist to copter
  int32_t  dir;         //temp variable to store dir to copter
  static uint32_t nav_loopTimer;

  //check that we have a valid frame, if not then return immediatly
  if (GPS_Frame == 0) return 0; else GPS_Frame = 0;

  //check home position and set it if it was not set
  if (f.GPS_FIX && GPS_numSat >= 5) {
    #if !defined(DONT_RESET_HOME_AT_ARM)
       if (!f.ARMED) {f.GPS_FIX_HOME = 0;}
    #endif
    if (!f.GPS_FIX_HOME && f.ARMED) {
      GPS_reset_home_position();
    }
    //Apply moving average filter to GPS data
    if (GPS_conf.filtering) {
      GPS_filter_index = (GPS_filter_index+1) % GPS_FILTER_VECTOR_LENGTH;
      for (axis = 0; axis< 2; axis++) {
        GPS_read[axis] = GPS_coord[axis]; //latest unfiltered data is in GPS_latitude and GPS_longitude
        GPS_degree[axis] = GPS_read[axis] / 10000000;  // get the degree to assure the sum fits to the int32_t

        // How close we are to a degree line ? its the first three digits from the fractions of degree
        // later we use it to Check if we are close to a degree line, if yes, disable averaging,
        fraction3[axis] = (GPS_read[axis]- GPS_degree[axis]*10000000) / 10000;

        GPS_filter_sum[axis] -= GPS_filter[axis][GPS_filter_index];
        GPS_filter[axis][GPS_filter_index] = GPS_read[axis] - (GPS_degree[axis]*10000000); 
        GPS_filter_sum[axis] += GPS_filter[axis][GPS_filter_index];
        GPS_filtered[axis] = GPS_filter_sum[axis] / GPS_FILTER_VECTOR_LENGTH + (GPS_degree[axis]*10000000);
        if ( NAV_state == NAV_STATE_HOLD_INFINIT || NAV_state == NAV_STATE_HOLD_TIMED) {      //we use gps averaging only in poshold mode...
          if ( fraction3[axis]>1 && fraction3[axis]<999 ) GPS_coord[axis] = GPS_filtered[axis];
        }
      }
    }

    //dTnav calculation
    //Time for calculating x,y speed and navigation pids
    dTnav = (float)(millis() - nav_loopTimer)/ 1000.0;
    nav_loopTimer = millis();

    // prevent runup from bad GPS
    dTnav = min(dTnav, 1.0);  

    //calculate distance and bearings for gui and other stuff continously - From home to copter
    GPS_bearing(&GPS_coord[LAT],&GPS_coord[LON],&GPS_home[LAT],&GPS_home[LON],&dir);
    GPS_distance_cm(&GPS_coord[LAT],&GPS_coord[LON],&GPS_home[LAT],&GPS_home[LON],&dist);
    GPS_distanceToHome = dist/100;
    GPS_directionToHome = dir/100;

    if (!f.GPS_FIX_HOME) {     //If we don't have home set, do not display anything
      GPS_distanceToHome = 0;
      GPS_directionToHome = 0;
    }

    //Check fence setting and execute RTH if neccessary
    //TODO: autolanding
    if ((GPS_conf.fence > 0) && (GPS_conf.fence < GPS_distanceToHome) && (f.GPS_mode != GPS_MODE_RTH) ) {
      init_RTH();
    }

    //calculate the current velocity based on gps coordinates continously to get a valid speed at the moment when we start navigating
    GPS_calc_velocity();        

    //Navigation state engine
    if (f.GPS_mode != GPS_MODE_NONE) {   //ok we are navigating ###0002 
      //do gps nav calculations here, these are common for nav and poshold  
      GPS_bearing(&GPS_coord[LAT],&GPS_coord[LON],&GPS_WP[LAT],&GPS_WP[LON],&target_bearing);
      if (GPS_conf.lead_filter) {
        GPS_distance_cm(&GPS_coord_lead[LAT],&GPS_coord_lead[LON],&GPS_WP[LAT],&GPS_WP[LON],&wp_distance);
        GPS_calc_location_error(&GPS_WP[LAT],&GPS_WP[LON],&GPS_coord_lead[LAT],&GPS_coord_lead[LON]);
      } else {
        GPS_distance_cm(&GPS_coord[LAT],&GPS_coord[LON],&GPS_WP[LAT],&GPS_WP[LON],&wp_distance);
        GPS_calc_location_error(&GPS_WP[LAT],&GPS_WP[LON],&GPS_coord[LAT],&GPS_coord[LON]);
      }

      // Adjust altitude 
      // if we are holding position and reached target altitude, then ignore altitude nav, and let the user trim alt
      if ( !((NAV_state == NAV_STATE_HOLD_INFINIT) && (alt_change_flag == REACHED_ALT))) {
        if (!f.LAND_IN_PROGRESS) {
          alt_to_hold = get_new_altitude();
          AltHold = alt_to_hold;
        }
      }

      int16_t speed = 0;                   //Desired navigation speed

      switch(NAV_state)                    //Navigation state machine
        {
        case NAV_STATE_NONE:               //Just for clarity, do nothing when nav_state is none
          break;

        case NAV_STATE_LAND_START:
          GPS_calc_poshold();              //Land in position hold
          land_settle_timer = millis();
          NAV_state = NAV_STATE_LAND_SETTLE;
          break;

        case NAV_STATE_LAND_SETTLE:
          GPS_calc_poshold();
          if (millis()-land_settle_timer > 5000)
            NAV_state = NAV_STATE_LAND_START_DESCENT;
          break;

        case NAV_STATE_LAND_START_DESCENT:
          GPS_calc_poshold();                //Land in position hold
          f.THROTTLE_IGNORED = 1;            //Ignore Throtte stick input
          f.GPS_BARO_MODE    = 1;            //Take control of BARO mode
          land_detect = 0;                   //Reset land detector
          f.LAND_COMPLETED = 0;
          f.LAND_IN_PROGRESS = 1;            // Flag land process
          NAV_state = NAV_STATE_LAND_IN_PROGRESS;
          break;

        case NAV_STATE_LAND_IN_PROGRESS:
          GPS_calc_poshold();
          check_land();  //Call land detector
          if (f.LAND_COMPLETED) {
            nav_timer_stop = millis() + 5000;
            NAV_state = NAV_STATE_LANDED;
          }
          break;

        case NAV_STATE_LANDED:
          // Disarm if THROTTLE stick is at minimum or 5sec past after land detected
          if (rcData[THROTTLE]<MINCHECK || nav_timer_stop <= millis()) { //Throttle at minimum or 5sec passed.
            go_disarm();
            f.OK_TO_ARM = 0;                //Prevent rearming
            NAV_state = NAV_STATE_NONE;     //Disable position holding.... prevent flippover
            f.GPS_BARO_MODE = 0;
            f.LAND_COMPLETED = 0;
            f.LAND_IN_PROGRESS = 0;
            land_detect = 0;
            f.THROTTLE_IGNORED = 0;
            GPS_reset_nav();
          }
          break;

        case NAV_STATE_HOLD_INFINIT:        //Constant position hold, no timer. Only an rcOption change can exit from this
          GPS_calc_poshold();
          break;

        case NAV_STATE_HOLD_TIMED:
          if (nav_timer_stop == 0) {                         //We are start a timed poshold
            nav_timer_stop = millis() + 1000*nav_hold_time;  //Set when we will continue
          } else if (nav_timer_stop <= millis()) {           //did we reach our time limit ?
            if (mission_step.flag != MISSION_FLAG_END) {
              NAV_state = NAV_STATE_PROCESS_NEXT;            //if yes then process next mission step
            }
            NAV_error = NAV_ERROR_TIMEWAIT;
          }
          GPS_calc_poshold();                                //BTW hold position till next command
          break;

        case NAV_STATE_RTH_START:
          if ((alt_change_flag == REACHED_ALT) || (!GPS_conf.wait_for_rth_alt)) {             //Wait until we reach RTH altitude
            GPS_set_next_wp(&GPS_home[LAT],&GPS_home[LON], &GPS_coord[LAT], &GPS_coord[LON]); //If we reached then change mode and start RTH
            NAV_state = NAV_STATE_RTH_ENROUTE;
            NAV_error = NAV_ERROR_NONE;
          } else {
            GPS_calc_poshold();                                                               //hold position till we reach RTH alt
            NAV_error = NAV_ERROR_WAIT_FOR_RTH_ALT;
          }
          break;

        case NAV_STATE_RTH_ENROUTE:                                                  //Doing RTH navigation
          speed = GPS_calc_desired_speed(GPS_conf.nav_speed_max, GPS_conf.slow_nav); 
          GPS_calc_nav_rate(speed);
          GPS_adjust_heading();
          if ((wp_distance <= GPS_conf.wp_radius) || check_missed_wp()) {            //if yes switch to poshold mode
            if (mission_step.parameter1 == 0) NAV_state = NAV_STATE_HOLD_INFINIT;
            else NAV_state = NAV_STATE_LAND_START;                                   // if parameter 1 in RTH step is non 0 then land at home
            if (GPS_conf.nav_rth_takeoff_heading) { magHold = nav_takeoff_bearing; }
          } 
          break;

        case NAV_STATE_WP_ENROUTE:
          speed = GPS_calc_desired_speed(GPS_conf.nav_speed_max, GPS_conf.slow_nav); 
          GPS_calc_nav_rate(speed);
          GPS_adjust_heading();

          if ((wp_distance <= GPS_conf.wp_radius) || check_missed_wp()) {               //This decides what happen when we reached the WP coordinates 
            if (mission_step.action == MISSION_LAND) {                                  //Autoland
              NAV_state = NAV_STATE_LAND_START;                                         //Start landing
              set_new_altitude(alt.EstAlt);                                             //Stop any altitude changes
            } else if (mission_step.flag == MISSION_FLAG_END) {                         //If this was the last mission step (flag set by the mission planner), then switch to poshold
              NAV_state = NAV_STATE_HOLD_INFINIT;
              NAV_error = NAV_ERROR_FINISH;
            } else if (mission_step.action == MISSION_HOLD_UNLIM) {                     //If mission_step was POSHOLD_UNLIM and we reached the position then switch to poshold unlimited
              NAV_state = NAV_STATE_HOLD_INFINIT;
              NAV_error = NAV_ERROR_FINISH;
            } else if (mission_step.action == MISSION_HOLD_TIME) {                      //If mission_step was a timed poshold then initiate timed poshold
              nav_hold_time = mission_step.parameter1;
              nav_timer_stop = 0;                                                       //This indicates that we are starting a timed poshold
              NAV_state = NAV_STATE_HOLD_TIMED;
            } else {
              NAV_state = NAV_STATE_PROCESS_NEXT;                                       //Otherwise process next step
            }
          }
          break;

        case NAV_STATE_DO_JUMP:
          if (jump_times < 0) {                                  //Jump unconditionally (supposed to be -1) -10 should not be here
            next_step = mission_step.parameter1;
            NAV_state = NAV_STATE_PROCESS_NEXT;
          }
          if (jump_times == 0) {
            jump_times = -10;                                    //reset jump counter
            if (mission_step.flag == MISSION_FLAG_END) {         //If this was the last mission step (flag set by the mission planner), then switch to poshold
              NAV_state = NAV_STATE_HOLD_INFINIT;
              NAV_error = NAV_ERROR_FINISH;
            } else
              NAV_state = NAV_STATE_PROCESS_NEXT;
          }

          if (jump_times > 0) {                                  //if zero not reached do a jump
            next_step = mission_step.parameter1;
            NAV_state = NAV_STATE_PROCESS_NEXT;
            jump_times--;
          }
          break;

        case NAV_STATE_PROCESS_NEXT:                             //Processing next mission step
          NAV_error = NAV_ERROR_NONE;
          if (!recallWP(next_step)) { 
            abort_mission(NAV_ERROR_WP_CRC);
          } else {
            switch(mission_step.action)
              {
              //Waypoiny and hold commands all starts with an enroute status it includes the LAND command too
              case MISSION_WAYPOINT:
              case MISSION_HOLD_TIME:
              case MISSION_HOLD_UNLIM:
              case MISSION_LAND:
                set_new_altitude(mission_step.altitude);
                GPS_set_next_wp(&mission_step.pos[LAT], &mission_step.pos[LON], &GPS_prev[LAT], &GPS_prev[LON]);
                if ((wp_distance/100) >= GPS_conf.safe_wp_distance)  abort_mission(NAV_ERROR_TOOFAR);
                else NAV_state = NAV_STATE_WP_ENROUTE;
                GPS_prev[LAT] = mission_step.pos[LAT];  //Save wp coordinates for precise route calc
                GPS_prev[LON] = mission_step.pos[LON];
                break;
              case MISSION_RTH:
                f.GPS_head_set = 0;
                if (GPS_conf.rth_altitude == 0 && mission_step.altitude == 0) //if config and mission_step alt is zero 
                  set_new_altitude(alt.EstAlt);     // RTH returns at the actual altitude 
                else {
                  uint32_t rth_alt;
                  if (mission_step.altitude == 0) rth_alt = GPS_conf.rth_altitude * 100;   //altitude in mission step has priority
                  else rth_alt = mission_step.altitude;

                  if (alt.EstAlt < rth_alt) set_new_altitude(rth_alt);                     //BUt only if we are below it.
                  else set_new_altitude(alt.EstAlt);
                }
                NAV_state = NAV_STATE_RTH_START;
                break;
              case MISSION_JUMP:
                if (jump_times == -10) jump_times = mission_step.parameter2;
                if (mission_step.parameter1 > 0 && mission_step.parameter1 < mission_step.number)
                  NAV_state = NAV_STATE_DO_JUMP;
                else //Error situation, invalid jump target
                  abort_mission(NAV_ERROR_INVALID_JUMP);
                break;
              case MISSION_SET_HEADING:
                GPS_poi[LAT] = 0; GPS_poi[LON] = 0; // zeroing this out clears the possible pervious set_poi
                if (mission_step.parameter1 < 0) f.GPS_head_set = 0;
                else {
                  f.GPS_head_set = 1;
                  GPS_directionToPoi = mission_step.parameter1;
                } 
                break;
              case MISSION_SET_POI:
                GPS_poi[LAT] = mission_step.pos[LAT];
                GPS_poi[LON] = mission_step.pos[LON];
                f.GPS_head_set = 1;
                break;
              default:                                  //if we got an unknown action code abort mission and hold position
                abort_mission(NAV_ERROR_INVALID_DATA);
                break;
              }
            next_step++; //Prepare for the next step
          }
          break;
        } // switch end
    } //end of gps calcs ###0002 
  }
  return 1;
} // End of GPS_compute

// Abort current mission with the given error code (switch to poshold_infinit)
void abort_mission(unsigned char error_code) {
  GPS_set_next_wp(&GPS_coord[LAT], &GPS_coord[LON],&GPS_coord[LAT], &GPS_coord[LON]);
  NAV_error = error_code;
  NAV_state = NAV_STATE_HOLD_INFINIT;
}

//Adjusting heading according to settings - MAG mode must be enabled
void GPS_adjust_heading() {
  //TODO: Add slow windup for large heading change
  //This controls the heading
  if (f.GPS_head_set) { // We have seen a SET_POI or a SET_HEADING command
    if (GPS_poi[LAT] == 0)
      magHold = wrap_18000((GPS_directionToPoi*100))/100;
    else {
      GPS_bearing(&GPS_coord[LAT],&GPS_coord[LON],&GPS_poi[LAT],&GPS_poi[LON],&GPS_directionToPoi);
      GPS_distance_cm(&GPS_coord[LAT],&GPS_coord[LON],&GPS_poi[LAT],&GPS_poi[LON],&wp_distance);
      magHold = GPS_directionToPoi /100;
    }
  } else {                                // heading controlled by the standard defines
    if (GPS_conf.nav_controls_heading) {
      if (GPS_conf.nav_tail_first) {
        magHold = wrap_18000(target_bearing-18000)/100;
      } else {
        magHold = wrap_18000(target_bearing)/100;
      }
    }
  }
}

#define LAND_DETECT_THRESHOLD 40      //Counts of land situation
#define BAROPIDMIN           -180     //BaroPID reach this if we landed.....

//Check if we landed or not
void check_land() {
  // detect whether we have landed by watching for low climb rate and throttle control
  if ( (abs(alt.vario) < 20) && (BaroPID < BAROPIDMIN)) {
    if (!f.LAND_COMPLETED) {
      if( land_detect < LAND_DETECT_THRESHOLD) {
        land_detect++;
      } else {
        f.LAND_COMPLETED = 1;
        land_detect = 0;
      }
    }
  } else {
    // we've detected movement up or down so reset land_detector
    land_detect = 0;
    if(f.LAND_COMPLETED) {
      f.LAND_COMPLETED = 0;
    }
  }
}

int32_t get_altitude_error() {
  return alt_to_hold - alt.EstAlt;
}

void clear_new_altitude() {
  alt_change_flag = REACHED_ALT;
}

void force_new_altitude(int32_t _new_alt) {
  alt_to_hold     = _new_alt;
  target_altitude = _new_alt;
  alt_change_flag = REACHED_ALT;
}

void set_new_altitude(int32_t _new_alt) {
  //Limit maximum altitude command
  if(_new_alt > GPS_conf.nav_max_altitude*100) _new_alt = GPS_conf.nav_max_altitude * 100;
  if(_new_alt == alt.EstAlt){
    force_new_altitude(_new_alt);
    return;
  }
  // We start at the current location altitude and gradually change alt
  alt_to_hold = alt.EstAlt;
  // for calculating the delta time
  alt_change_timer = millis();
  // save the target altitude
  target_altitude = _new_alt;
  // reset our altitude integrator
  alt_change = 0;
  // save the original altitude
  original_altitude = alt.EstAlt;
  // to decide if we have reached the target altitude
  if(target_altitude > original_altitude){
    // we are below, going up
    alt_change_flag = ASCENDING;
  } else if(target_altitude < original_altitude){
    // we are above, going down
    alt_change_flag = DESCENDING;
  } else {
    // No Change
    alt_change_flag = REACHED_ALT;
  }
}

int32_t get_new_altitude() {
  // returns a new altitude which feeded into the alt.hold controller
  if(alt_change_flag == ASCENDING) {
    // we are below, going up
    if(alt.EstAlt >=  target_altitude) alt_change_flag = REACHED_ALT; 
    // we shouldn't command past our target
    if(alt_to_hold >=  target_altitude) return target_altitude; 
  } else if (alt_change_flag == DESCENDING) {
    // we are above, going down
    if(alt.EstAlt <=  target_altitude) alt_change_flag = REACHED_ALT;
    // we shouldn't command past our target
    if(alt_to_hold <=  target_altitude) return target_altitude;
  }
  // if we have reached our target altitude, return the target alt
  if(alt_change_flag == REACHED_ALT) return target_altitude;

  int32_t diff  = abs(alt_to_hold - target_altitude);
  // scale is how we generate a desired rate from the elapsed time
  // a smaller scale means faster rates
  int8_t _scale = 4;

  if (alt_to_hold < target_altitude) {
    // we are below the target alt
    if(diff < 200) _scale = 4;
    else _scale = 3;
  } else {
    // we are above the target, going down
    if(diff < 400) _scale = 5;  //Slow down if only 4meters above
    if(diff < 100) _scale = 6;  //Slow down further if within 1meter
  }

  // we use the elapsed time as our altitude offset
  // 1000 = 1 sec
  // 1000 >> 4 = 64cm/s descent by default
  int32_t change = (millis() - alt_change_timer) >> _scale;

  if(alt_change_flag == ASCENDING){
    alt_change += change;
  } else {
     alt_change -= change;
  }
  // for generating delta time
  alt_change_timer = millis();

  return original_altitude + alt_change;
}

////////////////////////////////////////////////////////////////////////////////////
//PID based GPS navigation functions
//Author : EOSBandi
//Based on code and ideas from the Arducopter team: Jason Short,Randy Mackay, Pat Hickey, Jose Julio, Jani Hirvinen
//Andrew Tridgell, Justin Beech, Adam Rivera, Jean-Louis Naudin, Roberto Navoni

//original constraint does not work with variables
int16_t constrain_int16(int16_t amt, int16_t low, int16_t high) {
  return ((amt)<(low)?(low):((amt)>(high)?(high):(amt)));
}
////////////////////////////////////////////////////////////////////////////////////
// this is used to offset the shrinking longitude as we go towards the poles
// It's ok to calculate this once per waypoint setting, since it changes a little within the reach of a multicopter
//
void GPS_calc_longitude_scaling(int32_t lat) {
  GPS_scaleLonDown = cos(lat * 1.0e-7f * 0.01745329251f);
}

////////////////////////////////////////////////////////////////////////////////////
// Sets the waypoint to navigate, reset neccessary variables and calculate initial values
//
void GPS_set_next_wp(int32_t* lat_to, int32_t* lon_to, int32_t* lat_from, int32_t* lon_from) {
  GPS_WP[LAT] = *lat_to;
  GPS_WP[LON] = *lon_to;

  GPS_FROM[LAT] = *lat_from;
  GPS_FROM[LON] = *lon_from;

  GPS_calc_longitude_scaling(*lat_to);

  GPS_bearing(&GPS_FROM[LAT],&GPS_FROM[LON],&GPS_WP[LAT],&GPS_WP[LON],&target_bearing);
  GPS_distance_cm(&GPS_FROM[LAT],&GPS_FROM[LON],&GPS_WP[LAT],&GPS_WP[LON],&wp_distance);
  GPS_calc_location_error(&GPS_WP[LAT],&GPS_WP[LON],&GPS_FROM[LAT],&GPS_FROM[LON]);
  waypoint_speed_gov = GPS_conf.nav_speed_min;
  original_target_bearing = target_bearing;

}

////////////////////////////////////////////////////////////////////////////////////
// Check if we missed the destination somehow
//
static bool check_missed_wp(void) {
  int32_t temp;
  temp = target_bearing - original_target_bearing;
  temp = wrap_18000(temp);
  return (abs(temp) > 10000);   // we passed the waypoint by 100 degrees
}

////////////////////////////////////////////////////////////////////////////////////
// Get distance between two points in cm
// Get bearing from pos1 to pos2, returns an 1deg = 100 precision

void GPS_bearing(int32_t* lat1, int32_t* lon1, int32_t* lat2, int32_t* lon2, int32_t* bearing) {
  int32_t off_x = *lon2 - *lon1;
  int32_t off_y = (*lat2 - *lat1) / GPS_scaleLonDown;

  *bearing = 9000 + atan2(-off_y, off_x) * 5729.57795f;      //Convert the output redians to 100xdeg
  if (*bearing < 0) *bearing += 36000;
}

void GPS_distance_cm(int32_t* lat1, int32_t* lon1, int32_t* lat2, int32_t* lon2,uint32_t* dist) {
  float dLat = (float)(*lat2 - *lat1);                                    // difference of latitude in 1/10 000 000 degrees
  float dLon = (float)(*lon2 - *lon1) * GPS_scaleLonDown; //x
  *dist = sqrt(sq(dLat) + sq(dLon)) * 1.11318845f;
}

//*******************************************************************************************************
// calc_velocity_and_filtered_position - velocity in lon and lat directions calculated from GPS position
//       and accelerometer data
// lon_speed expressed in cm/s.  positive numbers mean moving east
// lat_speed expressed in cm/s.  positive numbers when moving north
// Note: we use gps locations directly to calculate velocity instead of asking gps for velocity because
//       this is more accurate below 1.5m/s
// Note: even though the positions are projected using a lead filter, the velocities are calculated
//       from the unaltered gps locations.  We do not want noise from our lead filter affecting velocity
//*******************************************************************************************************
static void GPS_calc_velocity(void){
  static int16_t speed_old[2] = {0,0};
  static int32_t last[2] = {0,0};
  static uint8_t init = 0;

  if (init) {
    float tmp = 1.0/dTnav;
    actual_speed[_X] = (float)(GPS_coord[LON] - last[LON]) *  GPS_scaleLonDown * tmp;
    actual_speed[_Y] = (float)(GPS_coord[LAT]  - last[LAT])  * tmp;

    //TODO: Check unrealistic speed changes and signal navigation about posibble gps signal degradation
    if (!GPS_conf.lead_filter) {
      actual_speed[_X] = (actual_speed[_X] + speed_old[_X]) / 2;
      actual_speed[_Y] = (actual_speed[_Y] + speed_old[_Y]) / 2;

      speed_old[_X] = actual_speed[_X];
      speed_old[_Y] = actual_speed[_Y];
    }
  }
  init=1;

  last[LON] = GPS_coord[LON];
  last[LAT] = GPS_coord[LAT];

  if (GPS_conf.lead_filter) {
    GPS_coord_lead[LON] = xLeadFilter.get_position(GPS_coord[LON], actual_speed[_X], GPS_LAG);
    GPS_coord_lead[LAT] = yLeadFilter.get_position(GPS_coord[LAT], actual_speed[_Y], GPS_LAG);
  }
}

////////////////////////////////////////////////////////////////////////////////////
// Calculate a location error between two gps coordinates
// Because we are using lat and lon to do our distance errors here's a quick chart:
//   100  = 1m
//  1000  = 11m    = 36 feet
//  1800  = 19.80m = 60 feet
//  3000  = 33m
// 10000  = 111m
//
static void GPS_calc_location_error( int32_t* target_lat, int32_t* target_lng, int32_t* gps_lat, int32_t* gps_lng ) {
  error[LON] = (float)(*target_lng - *gps_lng) * GPS_scaleLonDown;  // X Error
  error[LAT] = *target_lat - *gps_lat; // Y Error
}

////////////////////////////////////////////////////////////////////////////////////
// Calculate nav_lat and nav_lon from the x and y error and the speed
//
// TODO: check that the poshold target speed constraint can be increased for snappier poshold lock
static void GPS_calc_poshold(void) {
  int32_t d;
  int32_t target_speed;
  uint8_t axis;
  
  for (axis=0;axis<2;axis++) {
    target_speed = get_P(error[axis], &posholdPID_PARAM); // calculate desired speed from lat/lon error
    target_speed = constrain(target_speed,-100,100);      // Constrain the target speed in poshold mode to 1m/s it helps avoid runaways..
    rate_error[axis] = target_speed - actual_speed[axis]; // calc the speed error

    nav[axis]      =
        get_P(rate_error[axis],                                               &poshold_ratePID_PARAM)
       +get_I(rate_error[axis] + error[axis], &dTnav, &poshold_ratePID[axis], &poshold_ratePID_PARAM);

    d = get_D(error[axis],                    &dTnav, &poshold_ratePID[axis], &poshold_ratePID_PARAM);

    d = constrain(d, -2000, 2000);

    // get rid of noise
    if(abs(actual_speed[axis]) < 50) d = 0;

    nav[axis] +=d;
    // nav[axis]  = constrain(nav[axis], -NAV_BANK_MAX, NAV_BANK_MAX);
    nav[axis]  = constrain_int16(nav[axis], -GPS_conf.nav_bank_max, GPS_conf.nav_bank_max);
    navPID[axis].integrator = poshold_ratePID[axis].integrator;
  }
}

////////////////////////////////////////////////////////////////////////////////////
// Calculate the desired nav_lat and nav_lon for distance flying such as RTH and WP
//
static void GPS_calc_nav_rate( uint16_t max_speed) {
  float trig[2];
  int32_t target_speed[2];
  int32_t tilt;
  uint8_t axis;

  GPS_update_crosstrack();
  int16_t cross_speed = crosstrack_error * (GPS_conf.crosstrack_gain / 100.0);  //check is it ok ?
  cross_speed = constrain(cross_speed,-200,200);
  cross_speed = -cross_speed;

  float temp = (9000l - target_bearing) * RADX100;
  trig[_X] = cos(temp);
  trig[_Y] = sin(temp);

  target_speed[_X] = max_speed * trig[_X] - cross_speed * trig[_Y];
  target_speed[_Y] = cross_speed * trig[_X] + max_speed * trig[_Y];

  for (axis=0;axis<2;axis++) {
    rate_error[axis] = target_speed[axis] - actual_speed[axis];
    rate_error[axis] = constrain(rate_error[axis],-1000,1000);
    nav[axis]      =
        get_P(rate_error[axis],                        &navPID_PARAM)
       +get_I(rate_error[axis], &dTnav, &navPID[axis], &navPID_PARAM)
       +get_D(rate_error[axis], &dTnav, &navPID[axis], &navPID_PARAM);

    // nav[axis] = constrain(nav[axis],-NAV_BANK_MAX,NAV_BANK_MAX);
    nav[axis]  = constrain_int16(nav[axis], -GPS_conf.nav_bank_max, GPS_conf.nav_bank_max);
    poshold_ratePID[axis].integrator = navPID[axis].integrator;
  }
}

static void GPS_update_crosstrack(void) {
  // Crosstrack Error
  // ----------------
  // If we are too far off or too close we don't do track following
  float temp = (target_bearing - original_target_bearing) * RADX100;
  crosstrack_error = sin(temp) * wp_distance; // Meters we are off track line
}

////////////////////////////////////////////////////////////////////////////////////
// Determine desired speed when navigating towards a waypoint, also implement slow 
// speed rampup when starting a navigation
//
//      |< WP Radius
//      0  1   2   3   4   5   6   7   8m
//      ...|...|...|...|...|...|...|...|
//                100  |  200     300     400cm/s
//                 |                                        +|+
//                 |< we should slow to 1 m/s as we hit the target
//
static uint16_t GPS_calc_desired_speed(uint16_t max_speed, bool _slow) {
  if(_slow){
    max_speed = min(max_speed, wp_distance / 2);
  } else {
    max_speed = min(max_speed, wp_distance);
    max_speed = max(max_speed, GPS_conf.nav_speed_min);  // go at least nav_speed_min
  }
  // limit the ramp up of the speed
  // waypoint_speed_gov is reset to 0 at each new WP command
  if(max_speed > waypoint_speed_gov){
    waypoint_speed_gov += (int)(100.0 * dTnav); // increase at .5/ms
    max_speed = waypoint_speed_gov;
  }
  return max_speed;
}

////////////////////////////////////////////////////////////////////////////////////
// Utilities
//

int32_t wrap_36000(int32_t ang) {
  if (ang > 36000) ang -= 36000;
  if (ang < 0)     ang += 36000;
  return ang;
}


/*
 * EOS increased the precision here, even if we think that the gps is not precise enough, with 10e5 precision it has 76cm resolution
 * with 10e7 it's around 1 cm now. Increasing it further is irrelevant, since even 1cm resolution is unrealistic, however increased 
 * resolution also increased precision of nav calculations
*/

#define DIGIT_TO_VAL(_x)        (_x - '0')
uint32_t GPS_coord_to_degrees(char* s) {
  char *p, *q;
  uint8_t deg = 0, min = 0;
  unsigned int frac_min = 0;
  uint8_t i;

  // scan for decimal point or end of field
  for (p = s; isdigit(*p); p++) ;
  q = s;

  // convert degrees
  while ((p - q) > 2) {
    if (deg)
      deg *= 10;
    deg += DIGIT_TO_VAL(*q++);
  }
  // convert minutes
  while (p > q) {
    if (min)
      min *= 10;
    min += DIGIT_TO_VAL(*q++);
  }
  // convert fractional minutes
  // expect up to four digits, result is in
  // ten-thousandths of a minute
  if (*p == '.') {
    q = p + 1;
    for (i = 0; i < 4; i++) {
      frac_min *= 10;
      if (isdigit(*q))
        frac_min += *q++ - '0';
    }
  }
  return deg * 10000000UL + (min * 1000000UL + frac_min*100UL) / 6;
}

// helper functions 
uint16_t grab_fields(char* src, uint8_t mult) {  // convert string to uint16
  uint8_t i;
  uint16_t tmp = 0;

  for(i=0; src[i]!=0; i++) {
    if(src[i] == '.') {
      i++;
      if(mult==0)   break;
      else  src[i+mult] = 0;
    }
    tmp *= 10;
    if(src[i] >='0' && src[i] <='9') tmp += src[i]-'0';
  }
  return tmp;
}

uint8_t hex_c(uint8_t n) {    // convert '0'..'9','A'..'F' to 0..15
  n -= '0';
  if(n>9)  n -= 7;
  n &= 0x0F;
  return n;
} 

//************************************************************************
// Common GPS functions 
//
void init_RTH() {
  f.GPS_mode = GPS_MODE_RTH;           // Set GPS_mode to RTH
  f.GPS_BARO_MODE = true;
  GPS_hold[LAT] = GPS_coord[LAT];      //All RTH starts with a poshold 
  GPS_hold[LON] = GPS_coord[LON];      //This allows to raise to rth altitude
  GPS_set_next_wp(&GPS_hold[LAT],&GPS_hold[LON], &GPS_hold[LAT], &GPS_hold[LON]);
  NAV_paused_at = 0;
  if (GPS_conf.rth_altitude == 0) set_new_altitude(alt.EstAlt);     //Return at actual altitude
  else {                                                            // RTH altitude is defined, but we use it only if we are below it
    if (alt.EstAlt < GPS_conf.rth_altitude * 100) 
      set_new_altitude(GPS_conf.rth_altitude * 100);
    else set_new_altitude(alt.EstAlt);
  }
  f.GPS_head_set = 0;                                               //Allow the RTH ti handle heading
  NAV_state = NAV_STATE_RTH_START;                                  //NAV engine status is Starting RTH.
}

void GPS_reset_home_position(void) {
  if (f.GPS_FIX && GPS_numSat >= 5) {
    GPS_home[LAT] = GPS_coord[LAT];
    GPS_home[LON] = GPS_coord[LON];
    GPS_calc_longitude_scaling(GPS_coord[LAT]);    //need an initial value for distance and bearing calc
    nav_takeoff_bearing = att.heading;             //save takeoff heading
    //TODO: Set ground altitude
    f.GPS_FIX_HOME = 1;
  }
}

//reset navigation (stop the navigation processor, and clear nav)
void GPS_reset_nav(void) {
  uint8_t i;

  for(i=0;i<2;i++) {
    nav[i] = 0;
    reset_PID(&posholdPID[i]);
    reset_PID(&poshold_ratePID[i]);
    reset_PID(&navPID[i]);
    NAV_state = NAV_STATE_NONE;
    //invalidate JUMP counter
    jump_times = -10;
    //reset next step counter
    next_step = 1;
    //Clear poi
    GPS_poi[LAT] = 0; GPS_poi[LON] = 0;
    f.GPS_head_set = 0;
  }
}

//Get the relevant P I D values and set the PID controllers 
void GPS_set_pids(void) {
  posholdPID_PARAM.kP   = (float)conf.pid[PIDPOS].P8/100.0;
  posholdPID_PARAM.kI   = (float)conf.pid[PIDPOS].I8/100.0;
  posholdPID_PARAM.Imax = POSHOLD_RATE_IMAX * 100;

  poshold_ratePID_PARAM.kP   = (float)conf.pid[PIDPOSR].P8/10.0;
  poshold_ratePID_PARAM.kI   = (float)conf.pid[PIDPOSR].I8/100.0;
  poshold_ratePID_PARAM.kD   = (float)conf.pid[PIDPOSR].D8/1000.0;
  poshold_ratePID_PARAM.Imax = POSHOLD_RATE_IMAX * 100;

  navPID_PARAM.kP   = (float)conf.pid[PIDNAVR].P8/10.0;
  navPID_PARAM.kI   = (float)conf.pid[PIDNAVR].I8/100.0;
  navPID_PARAM.kD   = (float)conf.pid[PIDNAVR].D8/1000.0;
  navPID_PARAM.Imax = POSHOLD_RATE_IMAX * 100;
  }
//It was moved here since even i2cgps code needs it
int32_t wrap_18000(int32_t ang) {
  if (ang > 18000)  ang -= 36000;
  if (ang < -18000) ang += 36000;
  return ang;
}













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/**************************************************************************************/
...

Testing:

Conclusion:

You can build your own Quadcopter flight controller using ready made open source code from open controllers such as this one MultiWii and using easy embedded systems platform like Arduino.

You can then make use of the ease of code and the less expensive components.

And this is sure an educational experience that makes you aware of all Quadcopter principals.

Source:

https://www.hackster.io/robocircuits/arduino-quadcopter-e618c6

Check our books on Amazon:

Learn By Making: Embedded Systems Tutorial for Students and Beginners

Embedded Systems, Electronics: My Projects Collection From Instructables