Specifications

AVR064

2529A–AVR–11/02

Application Overview This application note describes how to get started with the ATmega169 microcontroller

(MCU), the first AVR that has a built in LCD controller/driver. This application is a tem-

perature control application, including a Real Time Clock. It will monitor the temperature

through a sensor, and regulate the temperature if a heating/cooling unit is attached.

Figure 1. Application Overview

The LCD starts with scrolling the text: “STK502 example application for ATmega169”. It

is required that the example code is programmed into the ATmega169 and the hardware

is set up according to the section “Hardware Configuration” on page 6.

Select a desired temperature set point. When the temperature goes below this set point

value, the Heater I/O pin will go high, and a LED on STK500 will flash. When the tem-

perature goes above the set point value, the Cooler I/O pin will go high, and another

LED on the STK500 will flash. The duty cycle of the LED flashing will vary with the actual

temperature deviation from the set point (the greater the deviation is, the brighter the

LEDs will shine) The LCD will display time and temperature information. All data that is

presented on the LCD will also be sent through the UART-interface and can be received

by etc a standard terminal.

Pressing a button on the STK500 will toggle the different information on the LCD. This

information is:

• CLOCK: RTC running on the ATmega169

• DATE: Calculated from the RTC

• SET POINT: Selected temperature

• TEMPERATURE: Measured temperature

• OFFSET: Difference between the measured temperature and the set point

• CONTRAST: Shows all the segments available with the default hardware strapping.

Adjusting the CLOCK, DATE, SET POINT, or the CONTRAST can be done by using

three of the SWITCHES on the STK500. Since these switches are used for different

functions, there is a need for a menu system. See Figure 2 for an overview of how the

menus are arranged in this application.

ATmega169

ADC

I/O

STK500

SWITCHES

Heating/

Cooling

Unit

STK500

LEDS

NTC

Thermistor

Timer2

32 kHz