# 1024 PPR or 200 PPR - Help deciding

my question is:

I am trying to purchase a quadrature from sparkfun. My device will be a homemade string pot that will measure velocity of string movement and direction.

I have a spool installed on the sensor axle to generate a line length of 10-12 ft. I am approximating here but lets say max speed of line pull is 2 m/s.

At a spool circumference of .2794 m (so .2794 m/rev) and a max velocity of 2 m/s.

My math is showing 1.37 seconds for 2.74 m of line travel (10 ft) at 2 m/s which is 9.82 revolutions. Math comes out to be 7.16 rev/s or 429.6 RPM.

Can the arduino uno handle the 1024 without interrupts or is the 200 a better option. need to be accurate down to speeds of .01 m/s +/- .01.

Thanks!

my math differs

10 ft = 304.8 cm @ 2m/sec => 1.53 second
12 ft = 365.8 cm @ 2m/sec => 1.83 second

spool O = 27.94 cm

10 ft = 304.8 cm => 10.90 revolutions
12 ft = 365.8 cm => 13.09 revolutions

If your goal is to measure the speed +- 0.01 m/s you need to be able to make at least 200 samples in the time it does 2 m. 200 cm / sec => 7.16 revolutions /sec

From accuracy point of view 200 samples per second is the absolute minimum and will only work of you can measure time exact. As this latter is not possible you have to go for the 1024.

If the Arduino has nothing else to do you can do this in a polling fashion. Otherwise interrupts are almost mandatory.

robtillaart:
my math differs

10 ft = 304.8 cm @ 2m/sec => 1.53 second
12 ft = 365.8 cm @ 2m/sec => 1.83 second

spool O = 27.94 cm

10 ft = 304.8 cm => 10.90 revolutions
12 ft = 365.8 cm => 13.09 revolutions

If your goal is to measure the speed +- 0.01 m/s you need to be able to make at least 200 samples in the time it does 2 m. 200 cm / sec => 7.16 revolutions /sec

From accuracy point of view 200 samples per second is the absolute minimum and will only work of you can measure time exact. As this latter is not possible you have to go for the 1024.

If the Arduino has nothing else to do you can do this in a polling fashion. Otherwise interrupts are almost mandatory.

Thank you! so a 1024 is almost a must??. will have a display and IR, so most likely need an interrupt.

...
so a 1024 is almost a must??. will have a display and IR, so most likely need an interrupt.

Yes