View Full Version : Help in a little project

02-06-2013, 09:03 PM
I want to make a project of determining the value of g (acceleration due to gravity) at a given place. So what I plan is that a metallic spherical ball is placed on a capacitive touch sensor connected to a microcontroller. Below this touch sensor, at a fixed vertical disance h there will be another touch sensor. Now both the sensors are connected to the microcontroller. There will be an extrusion on the top sensor using which the user can manually remove the touch sensor. Once the touch sensor is removed, the ball is at free fall. The microcontroller records the time (the top sensor will give this information actually, because there will be change in resistance as soon as the metal ball is not with contact to the sensor). After a small interval of time the ball hits the lower sensor. This time is recorded by the microcontroller. The microcontroller records the time difference, let it be t.
Now the value of t being known, we can calculate the value of g by g= 2h/t^2.

But I am a complete novice in robotics. Can anybody please guide me in the process(i.e. what microcontroller should be used, which touch sensor will be most effective, how to connect the sensor to the microcontroller, what will be the code, etc)?

Please note that I don't want to display this value, but to store it within the microcontroller, since its value will be used later in the same project.

02-07-2013, 05:10 PM
I do not recommend a touch sensor approach , Capacitive sensors need capacitance and do not work instantly. Here is a simple approach. Buy a big diameter PVC pipe , then buy a object which is half it diameter.

Now use a led and a light detector to create a beam which breaks when the object passes by put one paid on top of pipe and another paid somewhere near the bottom , Start timer when the first sensors light beam is obstructed and end when seconds is obstructed. The difference can be used by you.

You may also use laser leds for better results.

02-07-2013, 11:10 PM
Vikas's suggestions are spot on. Capacitive touch sensors are not as fast as you might think and for time critical applications, you are much better off with IR or laser sensing.
Just to add, Vikas means pair wherever you read paid.

02-08-2013, 08:56 PM
Thank you sir. It was very helpful.