Chris Wallau ECE5330 November 17, 2008 Remote Thermometer and Display

Overview Key Features Two AVR units: Thermometer controller Display Controller Thermometer I 2 C Interface Digital 9-bit readout Display Four digit seven segment LED display BOMQuantity Atmel Mega16 AVR/STK 5002 DS1621 IC Thermometer1 LTC-4627JR LED 7 Segment Display1 DC327 PNP Tansistors4 4.7Kohm Resistors4 220 Ohm Resistors7 10Kohm Reistors2 2

Block Diagram AVR1AVR2 SPI Interface I 2 C Interface AVR Ports Direct Connection 4 Digit LED Display External Display Control Logic DS1621 Thermometer 3

Hardware: Thermometer DS1621 Digital Thermometer from Maxim IC Connected as I 2 C interface to PD1 and PD0 Temperature range: -55˚C to +125˚C Outputs 9-bit digital value Open Drain Interface requires 10KOhm pullup resistors on SDA and SCL 4

Hardware: Display LTC-4627 Quadruple Seven Segment Display from Lite-On Electronics Common Anode Design Decimal points and clock colon will not be used in this application. Requires each segment to be driven separately by time multiplexing which will be controlled through PNP transistors at the common anode points. Current limiting resistors required at the cathode points and then connected to I/O ports on the AVR. 5

Software: SPI Interface 6 Both AVRs will be tied together through the SPI port: PB[7:4] The AVR with the display attached will be defined as the master. The AVR with the thermometer will be defined as the slave. The Master will shift All 1’s pattern to the Slave to indicate that it is ready for updated information. The Slave will place upper 8 bits of the thermometer output in the outgoing register. The Master will then shift the data in. This loop will be continuous and be contained in interrupt service routines.

Software: Thermometer 7 The thermometer IC that has been chosen utilizes Inter-Integrated Circuit communication (I 2 C) I 2 C is a protocol-based communications system. CodeWizard provides specific library functions for the DS1621 thermometer IC. These functions will be utilized. After initialization, a timer interrupt service routine will prompt the DS1621 thermometer IC for the most current temperature. An 8-bit code representing the temperature in whole degrees Celsius will be received and written to the SPI outgoing data register. The ninth bit received from the DS1621 represents a ½ degree Celsius and will be ignored for this application.

Software: Display 8 The AVR Ports must control the logic that drives the 7- segment display. Each segment of the display must be controlled individually (time multiplexed) due to the cathode connection. Timer interrupt service routines will control the time multiplexing of the segment display. The software will receive the 8-bit code read from thermometer AVR and decode this to drive the proper segments of each digit of the display.