For last two months i have studied lots of literatures related to Ballistic Chronograph and have done various R&D to test various logics practically,
I think this is the time to explain little ,to elaborate the principals logics and many other things about Ballistic Chronograph
Lets start with the basic principle, with simple wordings to make it understandable to all members, to make the technology more lucid
How Chronograph works
In ballistic chronograph the bullet or pellet travels from one end to other through a predefined distance..the entry end exit of the projectile
Is trapped in sensors, then the entry and exit time is captured and by subtracting one from another the elapsed time in milliseconds(as projectiles are very fast for example 800 fps) .As the distance is small so minimum unit is required to capture the appropriate time elapsed. then the processor divide the predefined distance by elapsed time and calculate the velocity, then the display circuitry is engaged to show its in readable form, often lcd or seven segment leds are used to display circuitry
What about Sensors
Sensors are device that react to specific physical activity and convert the change into electrical signals. The sensors reacting time should be fast enough to capture the projectile motion otherwise it will remain idle while the projectile passes both the end..
So what I discovered by various R&D process that the reaction time of both the sensors should be lesser than the projectiles passing time.Imagine a moving target which is moving at 1000 FPS and you are shooting with a 10 fps rifle..can u hit it..
![Smile :)](./images/smilies/icon_smile.gif)
On the other hand if you are having a 1000 FPS rifle and shooting a target moving at 10 fps,you will be able to hit it easily……This simple logic applies in sensors sensitivity.
In my prototype I have used IR sensors and further Amplified its signals by advance electronic circuit to enhance their effectiveness.
Sensing area and sensitivity responsiveness are others two factors which should be taken into consideration to build a chrony…if sensors are using light beams of 5 mm and pellet of 4.5 mm is passing through it it will be hard for the sensors to react promptly as beams are partially broken…So, after much R&D ,I have incorporated sensitivity adjustment mechanism in my chronograph so that each time and every time its detects the pellet.
What happens if the sensors are Slow?.....
If both the sensors are slow by say X millisecond. Then time taken will be with error of X milliseconds
Say First sensors time=t1+X and Second sensors time =t2+X,
So the elapsed time T=(t2+X)-(t1+X)= t2-t1
So you can notice that the delay is cancelled in the equation, So delay does not play any role if it is equal for each sensors.
The Processing Unit
Processing unit is a chip that interprets the input signals sent by the sensors and interpret the result and send data to display unit.
I have used Atmega 328 for this Purpose…
These Arduino Boards are having Crystal oscillators to keep track of time of various frequency..In my circuit its 16 Mhz,In Pratikjis Circuit its
8 Mhz,
Higher the number higher the resolution..16 Mhz ossilarators can take pulse in every 4Milisecons,Events in between can not be trapped by the device….
So the time elapsed will be always in the multiples of 4 in case of 16 Mhz and 8 in case of 8 Mhz,
So if elapsed time is actually 350 Milliseconds for 6 Inch or 0.5 foot ,Actual velocity=(0.5*1000000/350)=1428.57;
But the chrony will take the time in multiple of 4 =352 Milliseconds so Calculate velocity=(0.5*1000000/352)=1420.45;
So the deviation is ofvious in case of chronographs..More the mhz of oscillator more the accuracy….
Rest of the Things will be explained in further posts…
Thank You