Interia Dyno Project/Speed Sensor and other bits

Projects General Guidance
1

Hey there,

A friend and i are planning on creating an inertia dyno. With me doing the electronics probabaly with a UNO.

The plan at the moment is to use a hall effect device to measure the revloutions per minute of a rolling drum. Probabaly this http://www.jaycar.co.nz/productView.asp?ID=ZD1900&keywords=hall+effect&form=KEYWORD
Which will be a analog input (or digital) with the resistances going to inifnite with every rotation of the drum.

I could just datalog straight onto a SD card a millis() stamp everytime the sensor has something going past it.
However this would cause a extra step as i would then have to load the SD card in and import the txt file into the program which calculates the rpm etc

What would be the best way to automatically create a txt file on my PC's harddrive without going through the extra step of logging to a SD card?
I have read good things about GoBetWino.
Does the ArduIno software create a pretend COM port which you can then use a VB program to get the information into a txt file?

Any help would be great!

EDIT: To make a little more sense.

2

You can have the Arduino count the wheel rotations and calculate the speed at regular intervals e.g. 100ms and print it out over the serial port. The Arduino application software includes a USB driver which presents the Arduino's serial port as a virtual COM port that can be read by any application. For prototyping purposes you could just use the serial port monitor provided by the IDE, or anything else you can find that can read a COM port (older version of WIndows used to include a terminal application that could do it). Which one is best for you really depends what you want to do with the data. If you only want to load it into a spreadsheet and do your acceleration and torque calcs, using Gobetwino to log to a CSV format file would do that easily enough.

3

Thanks for that. I thought that was the case but its good to confirm it.

Not sure about getting it to calculate the rpm etc as then a minimum required speed of the roller would be required before it passed useful information across. 100ms being 10 revs per second or 600rpm which is about half the actual final speed, so alot of information would be missing (2000rpm would be the very maximum speed).
So in saying that perhaps i would need more than one reference point on my roller to determine the RPM. Which is easy to do.

On a side note realistically how long does it take for a Arduino Microcontroller (do they have higher clock speeds on some variants?) to read a analog or digital input and output it to a serial. 2000RPM is only 33.3HZ (30ms)
Thanks! I'm a complete newbie... I have only built one other arduino project, being a basic datalogger. But have a background in some electronics and programming!

4

For your free dyno progrma check here.
Only needs a reflective optocoupler with voltage devider to the MIC jack of a windows PC.

Let me know if this suites your request without the UNO.

Paco