HOME BREW
TEMPERATURE
CONTROLLER
Neville DeWitt Pierrat
Connor Fiechtner
December 2 nd , 2011
OVERVIEW
 Project Background
 System Description
 Circuit
 Input and Output




Thermocouple Input
Heater Output
Pushbuttons
LCD
 Control Design
 System Model & Simulation
 Controller Development
 Programming
 State Machine
 Interrupts
THE PROJECT
 Implement a control algorithm
using a microcontroller
 Design friendly user interface
 Must be modular and self contained
 Promote saccharification of
various cereal grain starches
 Synthesize a disaccharide
isomaltose solution for organic
conversion to ethanol
THE SYSTEM
Control is achieved through sensing the temperature and changing the duty
cycle of the heater. The slow response of the system allowed a long sampling
time of 10s, permitting the use of interrupts without worr ying about timing.
 Arduino Duemilanove
 ATMEGA328
 16 Mhz clock
 10-bit A/D
 Electric Kettle heater
 1500W
 Thermocouple
 Solid State Relay
 Optically coupled
 LCD display
 Pump
CIRCUIT DIAGRAM
THERMOCOUPLE INPUT
 Thermocouple
 Data sheet included temperature – resistance table
 Exponential was fit to data
 Gives relation between Temperature and resistance
 Voltage Divider
 The board will read the voltage and convert to digital
Voltage:
digitizedvoltage ∗
Resistance:
∗
Temperature:
47.65 ∗ log
517.05
HEATER OUTPUT
 1500W Heater on 120VAC
 Salvaged from thrift-store electric kettle
 Draws
12.5
 Omron G3NA -225B 25A Solid State
Relay
 Allows Arduino to control current to
heater
 Optically Coupled
 Switched by 5VDC
 Cheaper than an otherwise identical 15A
version
TEMPERATURE CONTROL BUTTONS
 SPST Pushbuttons to Increment or
Decrement Temperature Setpoint
 Require 10kΩ Pull-down resistors
 Interrupt-based response
 Software debouncing ignores edges within
100ms of first edge
 Immediate LCD updates
LCD TEMPERATURE DISPLAY
 Common Toshiba HD44780 chipset
 Identical to that used in class




16x2 Character Display
Parallel Signaling
5V Operation
4- or 8-pin Data Bus
SYSTEM IDENTIFICATION
 Run system at steady state and plot the response of step
input (10% duty cycle to 90%)
LEAD COMPENSATOR DESIGN
 A lead compensator controller was designed to achieve and
maintain a temperature set point
 Closed-loop simulation of controller output and temperature
response:
PROGRAMMING
 Identification of two discrete states for PWM led to
development of time-dependent state machine
 Heater On State
 Heater Off State
 Control algorithm evaluated at the end of every PWM
period
 Current temperature display updates every second
 Interrupt routines adjust set point and update set point
display
RECAP
 Project Background
 Brewing beer
 System Description
 Electronic temperature control
 Input and Output
 Sensors and Buttons and a Heater
 Control Design
 Mathin’
 Programming
 State Machine with Interrupts
QUESTIONS?