
  12 September 1993           MGJ


INTRODUCTION
------------

This .tar format archive contains hardware construction plans, and operating
software, for a simple data-logging thermometer that connects to a Sun
SPARC workstation via the audio input jack.  It is simple -- 3 chips --
and remarkably cheap to build {neglecting the $5000+ you already paid
for the computer!}.  It allows you to make very formidable, official
looking plots of temperature vs time, with 0.5 degree F accuracy.

   (This was its original purpose; I wanted to show the building
    manager exactly how warm my work area gets on summer afternoons)

But of course it is also a working example of a simple way to build an
A/D interface between external hardware widgets and your SPARCstation.
Because the data goes into the computer's audio input jack, you don't
need to open the cabinet of your workstation.  This is a good thing;
your sysadmin would probably freak out if s/he saw you meddling with
the innards of your box.


CONTENTS
--------

    README                  - this text file
    calc_farenheit.c        - source code in C that performs A-to-D
    experts_only.txt        - how to build it even cheaper (for EXPERTS only)
    how_to_calibrate.txt    - a text file on calibrating the finished unit
    hints_and_tips.txt      - a text file that tries to help you along
    parts_list.txt          - a text file of the hardware parts needed
    schematic.ps            - PostScript schematic of the hardware
    thermometer_script      - a skeleton "csh" script for 24 hour operation


LIMITATIONS
-----------

1.  The device is powered from the wall socket, via a cheap AC
    adapter/transformer purchased surplus or from Radio Shack.
    So it needs to be near a 120VAC jack.  On the other hand,
    your SPARCstation does too :-).

2.  After you build it, you have to calibrate it.  Which means
    you gotta find a _reference_ thermometer.  Pain in the butt.
    But, once calibrated, you're set to go for life, AND, unlike
    a reference thermometer, this one continuously datalogs into
    a file.  Even at night and over the weekend.

3.  (I'm not kidding:) your coworkers will insist that you make
    one for them.  You get to hear joyful remarks like "Waaaah,
    it's hot in MY office toooooo.  You have to make one for MEEE
    so IIII can show the boss how miserable III am tooooo.  Waaah!"


GUARANTEE
---------

Before complaining, please count to five while you reflect upon
the price you paid for this information.

Then please carefully re-read the following:

   ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
   +                                                                  +
   +   UNCONDITIONAL GUARANTEE OF COMPLETE AND TOTAL SATISFACTION     +
   +  *************************************************************   +
   +                                                                  +
   +     If, for any reason, you are not completely satisfied,        +
   +     I am very sorry.                                             +
   +                                                                  +
   ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


  --- Mark Johnson
