I’ve just started a new project.
I’m going to use a PS/2 mouse to make a planimeter.
These are used to measure the area of a scale drawings or maps. These are
useful because they can measure irregular shapes. There are several manual
on the web for these that describe the operation.
I thought it might be appropriate to use a mouse because the invention of
the mouse was based on the planimeter.
First I started with mouse communications. I found a library called PS2 that
had routines for reading and writing a mouse. To my dismay, it only worked
on two of the mice I had to play with.
I’ve since written low level code to replace the ones in the library but I regret
that I’m not good enough at C to create a replacement library. I’'ve just
got the code inline.
I did find the data sheet for the Elan EM84510 and the web page:
to be quite useful.
I’ve done some experiments with both an optical and roller ball mouse.
The optical just wasn’t repeatable enough for the task.
The two roller ball mice I have where quite consistent at X and Y counts
when moving the mouse over several inches and back.
I suspect they will work about as good as a commercial planimeter.
I expect to make a polar planimeter. I will make the arms out of thin
oak with the grain aligned. My work with clocks indicates there are few
materials better, short of special materials like fuzzed quarts, invar or Zerodur,
for temperature length stability.
I’ve found some chromed beads at a craft shop for the joints. I can run
a screw through these with a spring for light tension that should keep the
joints from having any play but allow almost frictionless movement.
What I lack now and am looking for suggestions is the user interface.
I have one of the standard LCD 2 line display shield and I’ve been using
a UNO board.
It has 5 user switches. I do have a pot attached that I’ve used for other
projects but don’t think I should need it here.
I expect the minimum functions to include:
- Cumulative count of X
- Reset of count
- Count hold/start ( useful for larger areas that can be divided.
- Perimeter distance total ( may be useful but not usually a planimeter function )
- Inch/centimeter conversion ( possible other ratios like acres, kilometers, miles etc )
- Calibration method
- Entering scale factors ( like from maps scales ratios )
I suspect some should be done with a menu but I do hate things
that have to have one select menus, just for basic operation.
I’d think #3 should be default operation after power reset.
Any suggestions would be appreciated, especially how one could effectively
use the display and switches. I always have a harder time with user interfaces.