T
[email protected]
- Jan 1, 1970
- 0
I need to measure a 1cm diameter ball traveling at arround 300m/s.
Measure it to find out how fast it exactly moves.
I am considering using two laser pointers which each shine on a light
sensitive diode.
The diodes would be connected in series between the 5v bias and the
signal lead on a pc soundcard. The input lead will also be connected
to the ground lead over a high resistance resistor to pull down the
signal.
The idea is that when both diodes are lit, the signal wil be high and
a simply 44kHz wave recoding wil show a constant high level. When the
first beam is blocked, the signal goes to zero and high again when the
beam is again not obstructed. A little later it will again drop low
and go up.
I should now be able to measure the distance between the two falling
flanks and calculate the time.
Given that the ball will move through a beam in 0.03ms that is 1.4
sample (at 44kHz) where the signal will go low. That is not a lot. Can
I coult on a light sensitive diode to respond quickly enough for this
signal to be detected, or should I consider something else?
I can, if needed, place two mirrors and let the laser beam bounce
between them in such a way that the light is off the diode while the
bounding beam is blocked anywhere along its path. That could for
example give me a 10cm distance over which the light is off.
The readon I want to use a sound card and not just program my tructy
old atmel 8515 mcu, is that it will be so much more simple than having
to fiddle with displaying the measured time output from the
controller visually or by transmitting it to pc. Right now the project
is not about making a cool speed measurer, but only to be able to
measure the speed for other purposes.
Measure it to find out how fast it exactly moves.
I am considering using two laser pointers which each shine on a light
sensitive diode.
The diodes would be connected in series between the 5v bias and the
signal lead on a pc soundcard. The input lead will also be connected
to the ground lead over a high resistance resistor to pull down the
signal.
The idea is that when both diodes are lit, the signal wil be high and
a simply 44kHz wave recoding wil show a constant high level. When the
first beam is blocked, the signal goes to zero and high again when the
beam is again not obstructed. A little later it will again drop low
and go up.
I should now be able to measure the distance between the two falling
flanks and calculate the time.
Given that the ball will move through a beam in 0.03ms that is 1.4
sample (at 44kHz) where the signal will go low. That is not a lot. Can
I coult on a light sensitive diode to respond quickly enough for this
signal to be detected, or should I consider something else?
I can, if needed, place two mirrors and let the laser beam bounce
between them in such a way that the light is off the diode while the
bounding beam is blocked anywhere along its path. That could for
example give me a 10cm distance over which the light is off.
The readon I want to use a sound card and not just program my tructy
old atmel 8515 mcu, is that it will be so much more simple than having
to fiddle with displaying the measured time output from the
controller visually or by transmitting it to pc. Right now the project
is not about making a cool speed measurer, but only to be able to
measure the speed for other purposes.