PixHawk 2: Is it worth the price

Pixhawk is a popular Hardware platform designed by ETH Zurich students, Pixhawk supports its own autopilot and the popular Ardupilot flight stack. The first commercial version was distributed by 3DR robotics.  3DR produced several versions of pixhawk. The px4 documentation listed hardwares as below

  1. Pixhawk
  2. mRo Pixhawk
  3. mRobotics-X2.1
  4. HKPilot32
  5. Pixfalcon
  6. Dropix
  7. Pixracer
  8. MindPX
  9. MindRacer
  10. Cube (Pixhawk 2)
  11. Pixhawk 3 Pro
  12. Pixhack v3
  13. Pixhawk 4
  14. Pixhawk 4 Mini
  15. Pixhack v5
  16. Pixhawk Mini (Discontinued)

However the Pixhawk 2.1 /2 or Pixhawk Cube from profiCNC is at top of all comparing to price of other hardwares. Its price is around 5 times of the 3DR version of pixhawk. The processor is exactly same and the sensors are equivalent to others. Only difference is the mechanical design and the connectors. The machanical design provide good vabration damping needed for the sensors best performance.

Misleading Feature Advertisements on there website they are counting each multi sensor chip as a single sensor counting 29 sensors which is exactly same in other versions too. They did not published the sensor names although its available on their github page. Now hex aero too uploaded a datasheet.

FMU Main board sensors (Github Page)

• MPU9250 (or ICM 20xxx) integrated accelerometer / gyro.
• MS5611 Baro

IMU Board Sensors (Github Page)

• LSM303D integrated accelerometer / magnetometer.
• L3GD20 gyro.
• MPU9250 (or ICM 20xxx) Gyro / Accel
• MS5611 Baro

So all total 4 Gyro(3 on IMU 1 on Main board) and 2 barometers

Lets see what was pixhawk 1

  • ST Micro L3GD20H 16 bit gyroscope
  • ST Micro LSM303D 14 bit accelerometer / magnetometer
  • Invensense MPU 6000 3-axis accelerometer/gyroscope
  • MEAS MS5611 barometer

CUAV PixHawk v3


  • Accelerometers (3): LS303D, MPU6000, MPU9250/hmc5983
  • Gyroscopes (3): L3GD20, MPU6000, MPU9250
  • Compass (2): LS303D, MPU9250
  • Barometer (2): MS5611 X2


Pixhawk APM Ardupilot: History of Opensource UAV

All these opensource thing started with Chris Anderson CEO of 3DR. Founder of DIY Robocars, DIY Drones, Dronecode, ArduPilot. Formerly Editor of Wired. He started the website diydrones.com while working on lego based UAV. Now founders of both Pixhawk and Ardupilot Joined as Dronecode collaboration, but the ardupilot is still independently running with its own contributers.

Ardupilot and APM

2007: Chris published a video of his UAV. and started diydrones.com website

2008: Jordi Munoz build helicopter based UAV win sparkfun.

2009: Jordi and Chris joined to form 3DR robotics

May 2009 – First ArduPilot board (using thermopiles) released by Jordi/3DRobotics

Nov 2009 – ArduPilot code repository created by Jordi

July 2012 – PX4 released by ETH (Lorenz Meier,MikeS) / 3D Robotics

Jan 2013 Android GCS released(Droidplanner and andropilot)

Nov 2013: PixHawk Hardware released for PX4 by PX4 and 3DR, ArduPilot ported for pixhawk

oct 2014: foundation of Dronecode

March 2016: 3DR ends funding Ardupilot

Pixhawk Hardware and FlightStack

Lorenz Meier a Masters student at the Computer Vision and Geometry Lab at ETH Zurich wanted to enable a drone to fly autonomously using computer vision. But as there was no flight controller so he had to develop the drone before using it for computer vision experiments.

  • After DayNight work for 9 months his students built the drone and won european micro air vehicle competition in 2009.
  • The Platform was named as same as the student team name PixHawk.
  • 3D Robotics, which took over manufacturing and distribution.
  • Pixhawk team collaborated with ArduPilot to enabled them to run Ardupilot flight stack on the PX4 middleware on Pixhawk, so users had more choice.
  • Dronecode founded in 2014, Pixhawk Team joined Dronecode with all their employees.
  • Ardupilot and Dronecode(PX4 Team) separated with a declaration from both sides.

Which is popular PX4 or Ardupilot ? Ardupilot Vs PX4

Hardware Platform: APM is popular among hobbyists as a lowcost Hardware platform. But the APM boards come with 8bit AVR processor which are not first enough for good performance of the codes. Commercially Pixhawk Hardawre platform is used by 80% of manufacturers.

Softwares: The prefered flight stack for both commercial, Hobbyists and  researchers is Ardupilot on PX4 middleware running on Pixhawk. APM users too use Ardupilot on APM boards directly without middleware.

Which is actually better ?

For softwares i can’t say, beacause till now i have no experience with the PX4 Autopilot except the middleware used to run Ardupilot on Pixhawk hardware.

  • Comparing Hardware platform Pixhawk with APM is reaaly easy
  • 32bit Processor with More RAM space
  • Backup Processor
  • Higher Processor clock speed so the loop frequency
  • Redundant Sensors and Better sensors.

But if we are using Ardupilot on Navio2(Raspberry) we have high enough processing performance.



  1. Ardupilot History
  2. PX4 Launch News on diydrones
  3. Ardupilot Dronecode Separation Announcement by tridge(One of the top contributers)
  4. Pixhawk hardware and PX4 Flightstack history




DGCA India Drone rules: NPNT

On my last post I explained details of drone policy published on 27th Aug 2018, the policy was in draft for last 3 years. Now they published it but this is still incomplete. Here i am listing some issues which are still not clear.

1.NPNT Compliance

No Permission No Takeoff is a new concept in all over the world for controlling UAV usage and traffic. This is a Part of Digital Sky Platform which is yet to be released by DGCA India. User(pilot) Have to register himself(with UAOP) and the drone(with UIN) and then install a mobile App to get permission for each flight just before flying.

How NPNT works ?

  • User installs the Digital Sky App provided by DGCA.
  • Submit pilot registration number, indirectly all details of pilot.
  • Submit device UIN number, it means all details of the UAV/drone.
  • Before Flying you request for permission.
  • UIN, UAOP and the current location(latitude, longitude) transmitted to server
  • Server checks whether its green zone, yellow zone or red zone
  • Checks for other exceptional entries for no permission
  • and the UIN, UAOP validity
  • if everything is OK then permission sent the UAV directly through the NPNT device and an acknowledgement message to the user app.

But still the user have to report police for each flight which seems weird.

Incomplete How ?

  • When will be the digital sky Platform will be launched ?
  • What will be the API to integrate with drones ?
  • What will be procedure for 2way communication with ATS.(necessary for all drones except nano)

Now none of drone manufacturer know about the API, so it will take time atleast one month after DGCA releases the Digital sky platform API and integration details.

2. No rule for Spraying Drones

From market survey we learned that Indians are more interested in spraying drones compared to the imaging drones. But its clearly mentioned on the documents published by DGCA that spraying is not allowed till now. Indians are not so much aware of the other uses of drone in agriculture except spraying. NDVI scanning or classifier based data extraction from farm fields need good skill in computing.

3. SSR transponder or ADS-B Out

These devices will make the airspace safe but it will increase the cost by 2000 dollars(INR 140000/-) or more. Usually these devices are used in manned air vehicles like helicopter or planes. ADS-B Out system works like a beacon broadcasting its own position heading and other data in a open band. it is bulky for manned vehicles and costly too. uAvionix introduced a cheaper solution for drones. Here is a screenshot from google search.

While it is purely unnecessary for drones flying at 400 ft height if he is 10 km away from an airport, DGCA made this compulsory for all except nano class. No airplane is expected at 400ft in a fly safe zone.

GPS Parameters NMEA and RAW

If you are using a GPS/GNSS module in your project you need to understand the parameters passed through the NMEA sentences. But if you are working on RTK or some precision Location algorithm then you should know the RAW data parameters too. These Raw data are mostly vendor specific like ublox has ubx, trimble T0 T1 T2 format, sirf has its own format  and the universal format taken as input to most softwares is RINEX.

Lets first explore the NMEA data

NMEA stands for National Marine Electronics Association. As NMEA was developed as a communication protocol between marine electronic components. Each sentence starts with $ and ends with CR LFAll standard sentences have prifix of two letters in case of GPS only receivers its GP. Followed by letters that define sentence content. Some vendors add some propietary sentences like garmin PGRM and magellan PMGN. Here is a list of sentence prefixes

AAM – Waypoint Arrival Alarm
ALM – Almanac data
APA – Auto Pilot A sentence
APB – Auto Pilot B sentence
BOD – Bearing Origin to Destination
BWC – Bearing using Great Circle route
DTM – Datum being used.
GGA – Fix information
GLL – Lat/Lon data
GRS – GPS Range Residuals
GSA – Overall Satellite data
GST – GPS Pseudorange Noise Statistics
GSV – Detailed Satellite data
MSK – send control for a beacon receiver
MSS – Beacon receiver status information.
RMA – recommended Loran data
RMB – recommended navigation data for gps
RMC – recommended minimum data for gps
RTE – route message
TRF – Transit Fix Data
STN – Multiple Data ID
VBW – dual Ground / Water Spped
VTG – Vector track an Speed over the Ground
WCV – Waypoint closure velocity (Velocity Made Good)
WPL – Waypoint Location information
XTC – cross track error
XTE – measured cross track error
ZTG – Zulu (UTC) time and time to go (to destination)
ZDA – Date and Time

GGA this is the most simplest way to get the cordinates from the NMEA


     GGA          Global Positioning System Fix Data
     223211       Fix taken at 22:32:11 UTC
     4807.234,S   Latitude 48 deg 07.234' S
     02243.050,W  Longitude 22 deg 43.050' W
     1            Fix quality: 0 = invalid
                               1 = GPS fix (SPS)
                               2 = DGPS fix
                               3 = PPS fix
			       4 = Real Time Kinematic
			       5 = Float RTK
                               6 = estimated (dead reckoning) (2.3 feature)
			       7 = Manual input mode
			       8 = Simulation mode
     08           Number of satellites being tracked
     0.9          Horizontal dilution of position
     545.4,M      Altitude, Meters, above mean sea level
     46.9,M       Height of geoid (mean sea level) above WGS84
     (empty field) time in seconds since last DGPS update
     (empty field) DGPS station ID number
     *47          the checksum data, always begins with *

GSA or GPGSA (Satellites Active)

This provides the satellite numbers and precision accuracy of location


     GSA      Satellite status
     A        Auto selection of 2D or 3D fix (M = manual) 
     3        3D fix - values include: 1 = no fix
                                       2 = 2D fix
                                       3 = 3D fix
     04,05... PRNs of satellites used for fix (space for 12) 
     2.5      PDOP (dilution of precision) 
     1.3      Horizontal dilution of precision (HDOP) 
     2.1      Vertical dilution of precision (VDOP)
     *39      the checksum data, always begins with *

GSV (Satelites in view)

One GSV sentence can provide data fro 4 sattellites so multiple sentences required for all staelites in view. GSV includes all satelites in view whether its used for localising or not.


      GSV          Satellites in view
      2            Number of sentences for full data
      1            sentence 1 of 2
      08           Number of satellites in view

      01           Satellite PRN number
      40           Elevation, degrees
      083          Azimuth, degrees
      46           SNR - higher is better
           for up to 4 satellites per sentence
      *75          the checksum data, always begins with *

GLL (Geographic Latitude and Longitude)


     GLL          Geographic position, Latitude and Longitude
     4916.46,N    Latitude 49 deg. 16.45 min. North
     12311.12,W   Longitude 123 deg. 11.12 min. West
     225444       Fix taken at 22:54:44 UTC
     A            Data Active or V (void)
     *iD          checksum data

RMC (Recomonded Minimum)


     RMC          Recommended Minimum sentence C
     123519       Fix taken at 12:35:19 UTC
     A            Status A=active or V=Void.
     4807.038,N   Latitude 48 deg 07.038' N
     01131.000,E  Longitude 11 deg 31.000' E
     022.4        Speed over the ground in knots
     084.4        Track angle in degrees True
     230394       Date - 23rd of March 1994
     003.1,W      Magnetic Variation
     *6A          The checksum data, always begins with *


Ublox GPS Fake and Original

Earlier i have written a blog about RTK, where i have used ublox modules for RTKlib. Ublox GPS(GNSS actually) modules are famous for their cost to performance ratio. Another reason is RAW code phase data from GNSS receivers, although they don’t  support RAW output feature officially for their non-premium modules. Most of the opensource and commercial drones too started using ublox for low cost and better performance. This is the only GPS modules with Binary output in such low price range.

Now ublox modules are available every online electronics component supplier and amazon ebay flipkart too. But most of them seems to be fake.

  1. Module name written on enclosure is M8N but just over the TIN Casing something else M6 or M7(models with compass used for drones).
  2. Sometimes users peel of the sticker on the tin casing it shows a sticker/label with lower version M6 or M7
  3. The U-Center catch different name when queried for software and hardware version
  4. User complain about up-gradation failure
  5. Some users complain they are not getting Galileo Reception
  6. Some users fail to store the configurations they have changed
  7. Few people peeped whats under the tin case found few things missing
  8. Ublox M8 and M7 doesn’t support I2C memory but boards have I2C EEPROM

Well every case is different we will discuss every case,


M8Q or M8M as M8N

They have supplied a M8Q or M8M both are 30-40% cheaper than the M8N, they miss few things like 1.Low Noise amplifier, 2.Saw filter, 3.Flash Memory for multiple use(Firmware upgrade, configuration store..). They just change the sticker and sell it as a M8N. These are some times written as not upgradable as the firmware is in ROM. Here is one available at ublox m8n



M6/M7 stickers changed

its all M6( Neo-M6) they just change the sticker and sell it as M8N, they still perform good as they are atleast Neo-m6 or m7. User can easily find it through U-center application.


They used only the Core Chip M8030 from ublox


in this case they use it in several ways some vendors try to add up everything as in ublox M8N module. The flash memory, The SAW filter and the LNA on the module board. On board LNA is an extra for higher gain there is a LNA already inside the chip which obvious for GNSS Chips.  Here is a link of such a module available at Self Assembled m8n. These modules will perform same as ublox original module iff components are good.

HolyBro Uses LNA Chip MAX2659ELT+ , no flash, no SAW filter

RadioLink uses LNA Chip MMIC BGA715L7 from infineon and Murrata SAW filter(only on SE100 no in TS100)

Radiolink modules seems cheaper than holybro modules and with additional features.

Case 3.2

But this is not same for all cases. Most manufacturers just use the the core IC and other components except the flash memory LNA and SAW filter. These cases user cant detect through u-center because they put the original firmware. Sometimes it shows as the core chip only. Because of no LNA filter it can’t perform as good as the original module.


Modules with unnecessary chips and battery on board

For several reasons a memory chip is useless with M8N, and the battery too

  • M8N has inbiult flash memory for firmware and config
  • M8N doesn’t support I2C EEPROM as most of them use I2C AT24C512C EEPROM
  • Battery was earlier used for battery backed RAM storage in M6 and M7 modules, now its stored in flash

there are more possible cases of fraud, if you are going to use it for drone(with a inbuilt compass) then beware of communication modes available. Some manufacturers even create a fake I2C adress for the Non HCM58 compass chip, they use AK97 chip instead.

How to detect a fake M8N module ?

Memory Chip(Exception SQI Flash) or battery on board means its fake

Where can i Buy a genuine ublox m8n module

  • Directly from ublox, or try the
  • holibro m8n module from banggood
  • Here GPS( for indians purchase from indronesolutions they are certified distributer for proficnc products)
  • Navio2 board for raspiberry pi



Drone 1.0 from DGCA

Flying drones(UAS) in controlled or uncontrolled Airspace is prohibited for public in India and it will be same till 1st Dec 2018.  DGCA, the authority responsible for controlling air traffic in Indian airspace drafted a set of rule in 2016 and again in 2017 modified and published as a draft only.  On 27th August 2018 they published the first set of rules for controlling drones  allowing public to fly drones with permission.They have published 3 document related to this. These rule will be effective from 1st December 2018. Here i am listing the major points.

  • No rule for Hobby, DIY, Self-made drones seems not allowed. Getting clearance for DIY or non branded drone will be complex or near to impossible.
  • Currently none of the drones available in market compliant with the NPNT , the OEM need to integrate these things. NPNT is necessary for all drones which need UIN. Nano drones are exempted from UIN but still with conditions.
  • If you flying Inside a building still you need permission
  • For agriculture scanning/imaging is OK but spraying is not allowed till now.
  • Delivery is not allowed, so don’t expect amazon will send their drones to you.
  • Flying a nano drone in your friends marriage is not easy. You can fly it in your garden without any licences but not in a marriage.
  • Pilot licenses are valid for 5 years costs 25000/- and all other papers
  • UIN registraion is like RC not transferable costs
  • RPA operated by NTRO, ARC, and Central Intelligence Agencies are all free they can do whatever they want without or with permit.
  • NPNT compliant drone will not fly until it gets permission via digital sky platform app. Once flying request accepted it will be transmitted to drone via GSM will enabled for the requested flight.

Drone Classification

  1. Nano Drone : Less than equal to 250 gram
  2. Micro Drone : Greater than 250 gram less than or equal to 2 kg
  3. Small Drone : Greater than 2 K.G. less than or equal to 25 kg
  4. Medium Drone : Greater than 25 KG less than or equal to 150 kg
  5. Large Drone : Greater than 150 kg


UIN(Unique Identification Number) is equivalent to vehicle number in normal vehicles. Its needed for all drone above Nano. But in some case you need UIN for Nano too. If you are flying nano drone in a friends party then you need UIN. The UIN need to engraved on the vehicle or attached to vehicle and should be clearly visible. UIN fee is INR1000/-


Unmanned Aircraft Operator permit is needed for flying all drones except nano and micro drones in uncontrolled airspace(or inside a building) with a limit of 50 feet and 200 feet respectively.  Getting UAOP for first time costs INR 25000/- valid for 5 years and renewal costs INR 10000/-

Flying drone upto 400 ft. AGL and visual line of sight are allowed. However, you need to have the following equipment installed on your drones:

  • GNSS (GPS) for horizontal and vertical position fixing
  • Autonomous Flight Termination System or Return Home (RH) option
  • Flashing anti-collision strobe lights
  • RFID and GSM SIM Card/ NPNT compliant for APP based real time tracking
  • Fire resistant identification plate inscribed with UIN
  • Flight Controller with flight data logging capacity.
  • SSR transponder (Mode ‘C’ or ‘S’) or ADS-B OUT equipment h) Barometric equipment with capability for remote sub-scale setting i) Geo-fencing capability j) Detect and Avoid capability (compulsory for indian manufacturers)


Here they have mentioned the upper limit but didn’t mentioned limit at which one can fly without these equipments. NPNT device is neceassary as per their policy that is clear but the SSR transponder will be costly. They have specified manufacturers are permitted only if they mount all of these devices.


The DGCA Documents

  2. Do’s and Don’ts
  3. REquirements for manufacturer pilot and done

Fake URL with Non-Ascii domain names.

Two year ago there was a viral whats-app message with text “Spin the wheel to win Exciting gifts spin.amaᴢon.com ” The user checks the link address thinks its authenticated message and if i click here it will land me to an authenticated page. Here i am adding one more rule, whatsapp does not support hyperlink if you write a web url it will automatically translate to the link same as the text. So only way is some kind of software hack. As the meassage was spread through whatsapp i tried to debug through whatsapp web and DNS requests going out from my PC.

When I saw it on source code it was something different although the script used to send the message are writing exact message with correct link spin.amaᴢon.com (original link) The source on whatsapp web showing a different name spin.xn--amaon–x59a.com .
cyrillic domainSo here confusion is whatsapp does not accept user created hyperlink and these messages contain which suspected to be a manipulated deceptive link.

Now after two years again i received similar messages.5b62535f-7756-41de-a60a-36ed3d42184c

Hey ! Big Bazaar is giving FREE INR5000 shopping voucher to celebrate it’s 17th anniversary, Go here to get yours : http://www.bıgbazaar.com/anniversary Enjoy and thanks me later!.

this time the domain name was suspicious, the letter i is actually missing a dot above it. What we know is only ASCII characters are allowed in domain names so we cant expect a non ascii character.

But yes it is actually non-ascii. 3 year ago some name servers started distributing domain names with non-ascii characters. These non-ascii(mostly cyrillic) domain names when entered on a browser it automatically translated to ascii names like the one above.

Cyrillic/NONASCII —————— -|————- ——– ASCII Translation
——————- ——————– ———|———- ———————– ————————
spin.amaᴢon.com ——————–|———— spin.xn--amaon–x59a.com
bıgbazaar.com ————————-|——— xn--bgbazaar-tkbg.com
indiaसरकार.com ———————–|———- xn--india-10k6nb3e2c.com

So now its better to verify web links properly and still there is possibility as some Cyrillic characters looks exactly same. if site is added with a valid https/SSL certificate with the same name as its displaying then we can say the link is authenticated. Ignore SSL certficates issued by letsencypt or similar SSL providers.

Building a QuadCopter or MultiCopter

First of all lets get all the terminologies associated with QuadCopters.

What is the difference between RTF, BNF, PNP and ARF ?

  • RTF stands for Ready-to-Fly and it means the model you are buying comes complete with everything you need to get started – straight from the box! Have look at our ready to fly drones.
  • RTR stands for Ready-to-Run and it means that the RC car or boat comes with the transmitter, battery and charger. You can start racing without requiring any extra component.
  • BNF stands for Bind-N-Fly. Bind-N-Fly products come with everything you need except for a transmitter. With BNF products you can use the transmitter of your choice and bind it to the receiver included with the model.
  • PNP stands for Plug-N-Play. Plug-N-Play products come with everything you need except for a transmitter, receiver battery and charger. It does contain servos, motor and ESC.
  • ARF stands for Almost-Ready-to-Fly, this means the model needs some additional “need to complete” items before you can start flying. Common additional items include servo’s, motor, electronics, batteries and even glue.

What are the Components of a quad-copter ?

  • Frame
  • Motors
  • Propellers
  • ESCs
  • Battery
  • Flight Controllers
  • Receiver
  • Remote Control
  • Gimbal

Lets discuss about each of the components needed to build a quadcopter

Frame: Frames mostly designed of glass fiber or carbon fiber making them crash-worthy. There are different types of frame available in market starting from INR 1000/-($13) to INR 6000/- . Most frames come with a set of bolts needed to fix it. You may use quadcopter frame or a hexcopter frame the arms are same if you are using DJI ARF KIT, Only the center PCB shape changes.QWinOut-DIY-24G-6CH-KK-V23-F450-Flamewheel-RC-Quadcopter-4-Axle-UFO-Unassembly-Kit-RTFARF-Basic-Drone-0-6














Motors: Motors come in different varieties with different parameters for speed or RPM (1000KV i.e. 1000 Kilo Rev per second) and the turns of coil like 6T/10T/13T. What voltage it will support is also need to be checked while purchasing motors. Battery mostly support 2S to 4S (4S means 4 lipo cells)4 cells x 3.7v = 14.8v.

  2. WEIGHT & DIMENSIONS: 48g & Dia27.5 x 30mm
  3. MATERIAL & COLOUR: NA & Orange
  4. KV: 2200
  5. Max Efficiency: 80%
  6. Max Efficiency Current: 4-10A (>75%)
  7. Current Capacity: 12A/60s
  8. No Load Current @ 10V: 0.5A
  9. No. Of Cells: 2-3 Li-Poly
  10. Shaft Diameter: 3.17mm
  11. s-l500












Tracking whatsapp without coding

You can hide the “Last Seen” in whatsapp but the Online status is shown to strangers to and this can be used to monitor your sleeping pattern and can correlated with other persons online activity. A lot of data can be mined from this simple 1 bit data Online or offline.






If you want to track whatsapp with coding you may try WhatsSpy Public, the code repo is available on github the developer published it as a proof of concept. Now the repo admin says its no more working but you can use it with some modification to adopt with the new changes in communication protocol. Anyway its time consuming frustrating to update code which i don’t understand. So i tried my own method with minimal or no coding.

A screenshot from Whatspy Public, Showing online time of two different persons which may be a online meeting between both users.




The easyway is whatsapp web version, the UI shows user online or not(even from non friends/strangers). So here you just need a way to log the text in a specific node of the HTML  code rendered on the screen. That is very easy with Chrome Devtools. Open the Devtools (CTRL+SHIFT+I) find the ID of the element showing online status with selector tool. Now try the element on console whether you got the right name



So this is the right element, now write the script to repeat this with logging. i have added exceptions to avoid the error lines


setInterval(function() {
var dt = new Date();
var time = dt.getHours() + “:” + dt.getMinutes() + “:” + dt.getSeconds();
try {
var lastSeen = document.getElementsByClassName(“emojitext O90ur”)[0].innerText;
console.log(time +’ ‘+lastSeen);
catch(err) {

}, 5000);



Now for whatsapp web its necessary the phone client should be online too. Keeping a phone online always is not easy. Run it with Nox player(bluestack will not work). Now Connect the in web client, for this you need a camera on the nox. you may use a webcam or an android remote cam(droid cam) for this. Once both clients logged in run the script there. when you want to store the data right click on console to save the data collected.

But still if you have time try WhatsAPI or ChatAPI, you may extend that to very good revenue making Android/iphone App. All the Best.


Imaging for research

We are working on phenomics plants since 2014 although we are not directly involved in design of the systems still we have learnt things that matter in this type of imaging. here i am going list out few terms that used in imaging:

File:Lens aperture side.jpg

Lense Characteristics:

Chromatic aberration (abbreviated CA; also called chromatic distortion and spherochromatism) is an effect resulting from dispersion in which there is a failure of a lens to focus all colors to the same convergence point. It occurs because lenses have different refractive indices for different wavelengths of light. The refractive index of transparent materials decreases with increasing wavelength in degrees unique to each.

Spherical aberration is an optical effect observed in an optical device (lens, mirror, etc.) that occurs due to the increased refraction of light rays when they strike a lens or a reflection of light rays when they strike a mirror near its edge, in comparison with those that strike nearer the centre. It signifies a deviation of the device from the norm, i.e., it results in an imperfection of the produced image.

Defocus is the aberration in which an image is simply out of focus. This aberration is familiar to anyone who has used a camera, videocamera, microscope, telescope, or binoculars. Optically, defocus refers to a translation along the optical axis away from the plane or surface of best focus. In general, defocus reduces the sharpness and contrast of the image. What should be sharp, high-contrast edges in a scene become gradual transitions. Fine detail in the scene is blurred or even becomes invisible. Nearly all image-forming optical devices incorporate some form of focus adjustment to minimize defocus and maximize image quality.

The degree of image blurring for a given amount of focus shift depends inversely on the lens f-number. Low f-numbers, such as f/1.4 to f/2.8, are very sensitive to defocus and have very shallow depths of focus. High f-numbers, in the f/16 to f/32 range, are highly tolerant of defocus, and consequently have large depths of focus. The limiting case in f-number is the pinhole camera, operating at perhaps f/100 to f/1000, in which case all objects are in focus almost regardless of their distance from the pinhole aperture. The penalty for achieving this extreme depth of focus is very dim illumination at the imaging film or sensor, limited resolution due to diffraction, and very long exposure time, which introduces the potential for image degradation due to motion blur.

The amount of allowable defocus is related to the resolution of the imaging medium. A lower-resolution imaging chip or film is more tolerant of defocus and other aberrations. To take full advantage of a higher resolution medium, defocus and other aberrations must be minimized.

f-number/focal ratio/f-ratio/f-stop of an optical system such as a camera lens is the ratio of the system’s focal length to the diameter of the entrance pupil. It is a dimensionless number that is a quantitative measure of lens speed, and an important concept in photography.  It is the reciprocal of the relative aperture. The f-number is commonly indicated using a hooked f with the format f/N, where N is the f-number.

Diaphragm(IRIS is a type of diaphgragm) is a thin opaque structure with an opening (aperture) at its center. The role of the diaphragm is to stop the passage of light, except for the light passing through the aperture. Thus it is also called a stop (an aperture stop, if it limits the brightness of light reaching the focal plane, or a field stop or flare stop for other uses of diaphragms in lenses). The diaphragm is placed in the light path of a lens or objective, and the size of the aperture regulates the amount of light that passes through the lens. The centre of the diaphragm’s aperture coincides with the optical axis of the lens system.

Lens speed refers to the maximum aperture diameter, or minimum f-number, of a photographic lens. A lens with a larger maximum aperture (that is, a smaller minimum f-number) is called a “fast lens” because it can achieve the same exposure with a faster shutter speed. Conversely, a smaller maximum aperture (larger minimum f-number) is “slow” because it delivers less light intensity and requires a slower (longer) shutter speed.

A fast lens speed is desirable in taking pictures in dim light, or with long telephoto lenses and for controlling depth of field and bokeh, especially in portrait photography,[1] and for sports photography and photojournalism.

Lenses may also be referred to as being “faster” or “slower” than one another; so an f/3.5 lens can be described as faster than an f/5.6.

Prime lens is either a photographic lens whose focal length is fixed, as opposed to a zoom lens, or it is the primary lens in a combination lens system.

Confusion can sometimes result due to the two meanings of the term if the context does not make the interpretation clear. Alternative terms primary focal length, fixed focal length, and FFL are sometimes used to avoid ambiguity.

For 35mm film and full frame digital cameras (in which the image area is 36 by 24 millimeters) prime lenses can be categorized by focal length as follows:

  • 14 to 21mm: Ultra-Wide — Because these lenses are usually used at very close subject distances the resulting perspective can provide a dramatic, often extreme image that can be used to selectively distort a scene’s natural proportions.
  • 24 to 35mm: Wide — these lenses capture a wider field of view than a standard lens. Because they tend to be used at shorter distances the resulting perspective can show some distortion.
  • 50 mm: Standard — with a focal length near the 44mm image diagonal.
  • 85 mm: Portrait — A short telephoto lens that allows a longer subject to camera distance, to produce pleasing perspective effects, while maintaining useful image framing.
  • 135 mm: Telephoto — these lenses are used by action and sports photographers to capture faraway objects.
  • 200 to 500 mm: Super Telephoto — these are specialized, bulky lenses for sports, action, and wildlife photography.

A zoom lens is a mechanical assembly of lens elements for which the focal length (and thus angle of view) can be varied, as opposed to a fixed focal length (FFL) lens (see prime lens).

A true zoom lens, also called a parfocal lens, is one that maintains focus when its focal length changes.[1] A lens that loses focus during zooming is more properly called a varifocal lens. Despite being marketed as zoom lenses, virtually all consumer lenses with variable focal lengths use varifocal design.

The convenience of variable focal length comes at the cost of complexity – and some compromises on image quality, weight, dimensions, aperture, autofocus performance, and cost. For example, all zoom lenses suffer from at least slight, if not considerable, loss of image resolution at their maximum aperture, especially at the extremes of their focal length range. This effect is evident in the corners of the image, when displayed in a large format or high resolution. The greater the range of focal length a zoom lens offers, the more exaggerated these compromises must become.

A varifocal lens is a camera lens with variable focal length in which focus changes as focal length (and magnification) changes, as compared to parfocal (“true”) zoom lens, which remains in focus as the lens zooms (focal length and magnification change). Many so-called “zoom” lenses, particularly in the case of fixed lens cameras, are actually varifocal lenses,[1] which give lens designers more flexibility in optical design trade-offs (focal length range, maximum aperture, size, weight, cost) than parfocal zoom. These are practical because of auto-focus, and because the camera processor can automatically adjust the lens to keep it in focus while changing focal length (“zooming”) making operation practically indistinguishable from a parfocal zoom.

A parfocal lens is a lens that stays in focus when magnification/focal length is changed. There is inevitably some amount of focus error, but small enough to be considered insignificant.

Zoom lenses used for moviemaking applications must have the parfocal ability in order to be of practical use. It is almost impossible to stay in correct focus (as done manually by the focus puller) while zooming.

A lens mount is an interface – mechanical and often also electrical – between a photographic camera body and a lens. It is confined to cameras where the body allows interchangeable lenses, most usually the rangefinder camera, single lens reflex type or any movie camera of 16 mm or higher gauge. Lens mounts are also used to connect optical components in instrumentation that may not involve a camera, such as the modular components used in optical laboratory prototyping which join via C-mount or T-mount elements. Read more at wikipedia





Bokeh  is the aesthetic quality of the blur produced in the out-of-focus parts of an image produced by a lens. Bokeh has been defined as “the way the lens renders out-of-focus points of light”. Differences in lens aberrations and aperture shape cause some lens designs to blur the image in a way that is pleasing to the eye, while others produce blurring that is unpleasant or distracting—”good” and “bad” bokeh, respectively. Bokeh occurs for parts of the scene that lie outside the depth of field. Photographers sometimes deliberately use a shallow focus technique to create images with prominent out-of-focus regions.

An aspheric lens or asphere is a lens whose surface profiles are not portions of a sphere or cylinder. In photography, a lens assembly that includes an aspheric element is often called an aspherical lens.

The asphere’s more complex surface profile can reduce or eliminate spherical aberration and also reduce other optical aberrations such as astigmatism, compared to a simple lens. A single aspheric lens can often replace a much more complex multi-lens system. The resulting device is smaller and lighter, and sometimes cheaper than the multi-lens design.[1] Aspheric elements are used in the design of multi-element wide-angle and fast normal lenses to reduce aberrations. They are also used in combination with reflective elements (catadioptric systems) such as the aspherical Schmidt corrector plate used in the Schmidt cameras and the Schmidt-Cassegrain telescopes. Small molded aspheres are often used for collimating diode lasers.

Aspheric lenses are also sometimes used for eyeglasses. Aspheric eyeglass lenses allow for crisper vision than standard “best form” lenses, mostly when looking in other directions than the lens optical center.

Metering mode refers to the way in which a camera determines the exposure. Cameras generally allow the user to select between spot, center-weighted average, or multi-zone metering modes. Various metering modes are provided to allow the user to select the most appropriate one for use in a variety of lighting conditions.

With spot metering, the camera will only measure a very small area of the scene (between 1-5% of the viewfinder area). This will by default be the very centre of the scene. The user can select a different off-centre spot, or to recompose by moving the camera after metering.

Depth of field (DOF), also called focus range or effective focus range, is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. Although a lens can precisely focus at only one distance at a time, the decrease in sharpness is gradual on each side of the focused distance, so that within the DOF, the unsharpness is imperceptible under normal viewing conditions.

In some cases, it may be desirable to have the entire image sharp, and a large DOF is appropriate. In other cases, a small DOF may be more effective, emphasizing the subject while de-emphasizing the foreground and background. In cinematography, a large DOF is often called deep focus, and a small DOF is often called shallow focus.

Several other factors, such as subject matter, movement, camera-to-subject distance, lens focal length, selected lens f-number, format size, and circle of confusion criteria also influence when a given defocus becomes noticeable. The combination of focal length, subject distance, and format size defines magnification at the film / sensor plane.

DOF is determined by subject magnification at the film / sensor plane and the selected lens aperture or f-number. For a given f-number, increasing the magnification, either by moving closer to the subject or using a lens of greater focal length, decreases the DOF; decreasing magnification increases DOF. For a given subject magnification, increasing the f-number (decreasing the aperture diameter) increases the DOF; decreasing f-number decreases DOF.

Hyperfocal distance is a distance beyond which all objects can be brought into an “acceptable” focus. As the hyperfocal distance is the focus distance giving the maximum depth of field, it is the most desirable distance to set the focus of a fixed-focus camera. The hyperfocal distance is entirely dependent upon what level of sharpness is considered to be acceptable.

Focus stacking (also known as focal plane merging and z-stacking[1] or focus blending) is a digital image processing technique which combines multiple images taken at different focus distances to give a resulting image with a greater depth of field (DOF) than any of the individual source images.[2][3] Focus stacking can be used in any situation where individual images have a very shallow depth of field; macro photography and optical microscopy are two typical examples. Focus stacking can also be useful in landscape photography.