Cheap communicating calculator?

From: Dan Clemmensen (
Date: Wed Jan 30 2002 - 16:32:02 MST

This message is almost completely off-topic.

I want to replace the thermostats in my house with
a sophisticated computer-based system. Dedicated
home-control gear is expensive and clunky, but
I've finally found a perfect central controller
(A TINI--java based, ethernet, real-time, free SDK, $50.00)
  and the appropriate thermometers relays, etc. to go with it.

Oddly enough, the expensive part is the human interface:
A plain thermostats, in addition to a temperature sensor and
relay control, also displays the current temperature and the
current setpoint, and allows the user to change the setpoint.

The simplest acceptable purpose-built digital units with
a display, buttons, and wires to communicate to a central unit,
and pretty enough to hang on the wall, cost $50.00 to $100, and
I need at least 5. (I can use my computers for the rest of the rooms.)

However, I can purchase an HP38g graphing calculator for $50.00.
This unit is a fully programmable computer with a free SDK and
a serial interface. It has lots of buttons and a nice graphical
LCD, and would look nice hanging on the wall (OK, we are all techies
in this house!)

Question: are there any cheaper fully programmable calculators with
serial interfaces?

Extropian connections:
    --Well, we were just discussing calculators. :-)
    --This is an extreme example of general-purpose computers
(the calculator, in this instance) becoming so cheap as to displace
even the simplest purpose-built equipment.

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