This sketch uses a DS18B10 temperature sensor in conjunction with
a heating element and fountain pump to provide a precise water bath
controller for C-41 and E-6 color film processing.

Additionally, it drives a SainSmart 1602 LCD Display with Keypad
to allow the user to select processing chemistry and act as a timer
for the various steps involved (presoak, developer, blix, etc.)

It currently supports:

- Unicolor C-41 powder kit at 96F.  This is a lower temperature
  than usual to allow a color developer time greater than
  5 minutes (times under 5 minutes can cause unevenness in tank
  processing).

- Tetenal E-6 liquid kit at standard temps and times.

- Partial support for B&W

- "Emulsion mode" which keeps the water bath at 120F for making
  homebrew gelatin emulsions.

------------------
 EQUIPMENT NEEDED
------------------

- Arduino UNO or equivalent

- SainSmart 1602 LCD Display

- A suitably waterproofed DS18B10 temperature sensor such as 
  this one from Sparkfun: https://www.sparkfun.com/products/11050
  
- 4.7K pullup resistor for the DS18B10

- Relay rated for 5 amps or more at 120/240VAC depending
  on your country.  I used one from my junk box, but the SainSmart
  HL-52S should work.

- 300W coffee cup heater (aka 'electric immersion heater') such as
  this one from Amazon

  https://www.amazon.com/Norpro-Instant-Electric-Immersion-Heater/dp/B01M0Q84BR
  
- Small submersible fountain pump, such as this one:

  https://www.amazon.com/American-Pond-Fountain-2-4Watt-APJR150/dp/B00MKKWZVK/
  

------------------
     WIRING
------------------

The SainSmart LCD is plugged in normally.

The fountain pump is always ON; plug it into an AC outlet when
using the water bath controller. If you're handy with AC wiring
you can wire up a duplex outlet to have one always ON socket for
the pump and connect the other socket to the heater element relay.

Wiring the temperature sensor:

+5V ---------------> DS18B20 V+
                        |
                   4.7K resistor
                        |
Arduino pin 12 ----> DS18B20 DATA


GND ---------------> DS18B20 GND


Wiring the relay module:

=5V ----------------> Relay module V+

Arduino pin 13 -----> Relay module control pin

GND ----------------> Relay module GND


Wiring the heater element:

RELAY_NC (normally closed)  Not connected
RELAY_NO (normally open)    One wire of heater's AC cord
RELAY_COMMON (contact arm)  AC hot wire

Connect the AC neutral wire to the other wire of the heater's AC cord.


------------------
    OPERATING
------------------

WARNING: do NOT apply power to the Arduino until both the
heating element and temperature sensor are immersed in
the water bath!

1. Fill up a shallow plastic tub with water.  This tub
   should be large enough to hold your chemistry and
   your film tank.  Chemistry should be pre-measured
   and poured into Ziploc bags or pint jars.  Make
   sure to heat up your presoak water as well!
   
2. Place the fountain pump in the water bath and turn it
   on.  Position it so water circulates nicely around the
   entire bath.
   
3. Place the heater in the water bath immediately in the
   path of water coming out of the pump.
   
4. Place the temperature sensor in the water bath.

5. Turn on the Arduino and select your film process and
   push/pull stops.
   
6. Allow the water bath to come to temperature (it may take
   15 minutes or so).  Once at process temp, allow another
   15 minutes to ensure the chemistry is at the correct
   temperature as well.
   
7. Pour your presoak water into your tank and click NEXT. The
   LCD will show times for each of your process steps.