Parallel port dynamometer with Python
Cremona, around 200000 BC.
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I just found in a corner of my garage this dynamometer prototype.
It works by reading the state of a potentiometer via a parallel port, using python.
The goal was measuring the thrust generated by some small candy rockets.
I was probably a freshman in engineering school back then, and you can guess I had
not much aquaintance with data acquisition systems!
If you need to measure rockets thrust I'd suggest you of course to use load cells.
Check out this document HERE
for a homemade load cell and
HERE
for a tri-axial load cells calibration.
The idea is that the force will be proportional to the displacement (there are two
springs at the bottom), and we probe this displacement by connecting a potentiometer.
The potentiometer is put as a branch of a NE555 monostable timer:
- The current time is saved in a variable;
- The monostable 555 is started with a pulse from the parallel port.
The 555 output will be on for a duration that depends on the potentiometer;
- When the 555 output goes down, the time is probed again;
- The resistance of the potentiometer is found by checking how much time has
passed (in the order of ms).
In the following pictures you can see the system (sorry, I have no schematic at the moment),
the python script and an image output (produced by the script).
CLICK TO OPEN THE IMAGES
Cheers!
Stefano
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