INTRODUCTION:
=============
THERMYv3 is a continuation of the thermy project into a third design
phase, as the previous two designs were insufficient electrically
and in general. Hopefully, THERMYv3 will be the final design in the
thermy series, and I can wrap this project up. :)

THERMY PURPOSE:
===============
The thermy project's intent is to create a standalone electronic device
that is capable of digitally displaying the ambient temperature. The
thermy design is unique in that is uses a completely digital pathway
between its sensor (The Maxim IC DS18B20+) and the microcontroller
(The Atmel AVR ATmega8).

ERRATA ADDRESSED BY THERMYv3:
=============================
As is probably clear by this time, previous designs of the thermy
device have failed to produce a working proof-of-concept, so this
third revision was specifically designed to address these issues:

  1. COMPONENT AVAILABILITY: The first two thermy designs required parts
     from digikey, sparkfun electronics, and radioshack. THERMYv3 only
     requires parts (excluding the PCB from batchpcb) from digikey.

  2. ELECTRONIC DESIGN ERRORS: Serious errors in the thermy schematics
     of v1 and v2 are present which will limit or inhibit proper electric
     functionality:
       a. Improper Anode/Cathode for LEDs: v1 and v2 used a common-cathode
          seven-segment led display, but the schematics were made for the
          common-anode type.
       b. Absense of Proper Resistors: v1 was completely devoid of any
          pull-up or current-limiting resistors on AVR ports and the
          sensor bus, and v2 lacked a 4.7k pull-up resistor on the
          sensor one-wire bus.
       c. Absence of a required Capacitor: v3 finally adds a crucial
          0.10u capacitor between the GND and VCC pins of the AVR
          that will provide current at times when the AVR pulls more
          than provided by the LM7805 regulator.
       d. Absence of a Physical RESET: v3 provides an external reset
          switch, just in case. :)

  3. PHYSICAL DESIGN ERRORS: Previous designs lacked various finishing
     touches which either reduced usability or completely blocked
     functionality:
       a. Incorrect ISP Header: Previous designs features a 10-pin
          In-System Programming (ISP) header, which is not directly
          compatible with the 6-pin programming header of the STK500v2.
       b. Wrong Resistor Footprints: v2 used a very small footprint
          for all of the resistors, which forced all resistors to be
          soldered at precarious angles.
       c. Proximity of Sensor and Regulator: In the v2 design, the
          LM7805 regulator was relatively close to the DS18B20
          temperature sensor, meaning any increase in temperature
          due to the VREG would show up.
       d. Size of LED Displays: v1 and v2 both used the LITE-ON
          HD-A103, which is a 0.8" display. v3 uses an HD-F101,
          which is a 1.0" display.
       e. Incorrect Sensor Pinout: The hacked pinout of the DS18B20
          in the v1 and v2 designs did not match the actual pinout
          of the device, requiring further external wiring.

FUNCTIONALITY WALKTHROUGH:
==========================
When thermy boots it initializes the 1-Wire Bus and sets up the LED
displays. During the control loop, the AVR polls the DS18B20+ sensor
for temperature values and updates the displays with the previous
value during the 750ms required by the sensor to collect a new
measurement. For more details, see the thermy source code.

PARTS MANIFEST:
===============
Here's the components manifest for the THERMYv3 design. All parts are
available from digikey, which simplifies component orders and also
makes the entire design cheaper to build.

The "Req" column tells the number of each component a design requires,
the "Min" column tells the minimum order quantity of each component,
the "Buy" column tells the number of each component purchased to meet
both the previous requirements, and the "Part Number" column is obvious.

 +--------------------------------------+
 | ** DIGIKEY:                          |
 +--------------------------------------+
 | Req Min Buy   Part Number            |
 +--------------------------------------+
 | 1   1   1     ATMEGA8-16PU-ND        |
 | 1   1   1     CTX082-ND              |
 | 1   1   1     SAM1030-03-ND          |
 | 1   1   1     LM7805CT-ND            |
 | 4   1   4     PN2907ABUFS-ND         |
 | 4   1   4     160-1578-5-ND          |
 | 2   1   2     399-4344-ND            |
 | 2   1   2     399-3507-ND            |
 | 1   1   1     399-4408-ND            |
 | 8   5   10    220H-ND                |
 | 5   5   5     4.7KH-ND               |
 | 1   5   5     10KH-ND                |
 | 1   1   1     DS18B20+-ND            |
 | 1   1   1     CKN6012-ND             |
 | 1   1   1     SW404-ND               |
 | 1   1   1     AE10286-ND             |
 |                                      |
 +--------------------------------------+