Brew Controller - Specification

The aim for the new brew controller is to control the brew day. This could be built to varying budgets (probably around £200 in what I'm building) primarily determined by the power rating. I am of the view two elements is better than one but haven't actually specified the elements for the boiler yet- the HLT elements are standard kettle elements ~ 11amps each. I'm taking a view that things which can't easily be replaced should aim for 20A - but to keep control on the cost intiially some easily replaced switches are only good for 15A.

In the garage I'm likely to have 1 x 30amp feed and 1 x 13amp feed, two 15A zones is an improvement over the current ATC800+ based temperature controller which is only good for a single 13A zone.

Specifications

• 2 x Diverse - Power Zones
• Control of HLT for heating the mash water, and sparge water. 
• Control of Boil control
• Control of fermentation (to replace existing ATC800+), and provide graph of fermentation temperature
• Automatic control of extractor fan
• Manual control of 1 Pump
• Ability to drive the functions from the brew controller, with (perhaps) of remote triggering of functions over a network interface.
• Base settings for a given receipes should be set from a network interface to avoid manually setting values
• Ability for real-time status to be seen over the network (web interface, android app) 
• Allow future expansion to RIMS/HERMS
• Hardware wise additional pumps may be required and control would move to software

Basic Equipment

• RaspberryPi for control. 
• In the previous temperature controller there was stability issues with running two DS18B20 probes. In hindsight this may have been a hardware wiring issue. Since I have a spare RPi two will be used to spread the load. (Testing will determine if refactoring onto a single RPi has any downsides).
• DS18B20 probes for temperature control
• HD44780 20x4 LCD screen 
• previously used a 16x2 which was a little too limiting
• SSR's for controlling element (1 per zone)
• Mechanical Relays to protect element sockets 
• Mechanical Relays to control low-power devices (fridge, heater, extractor fan, pump).
• Lot's of switches, buttons, wire, sockets and plugs, resistors, transistors
• MCP23017 I2C switch for providing extra GPIO ports.
• Old computer case to house it all in.

Parts gathered so far