Written By: Andrew Fung
April 24, 2002
Etec 475
Hardware Description
The main purpose of this project will be to monitor outside weather conditions and provide accurate readings to a display for a user to monitor. The weather station will be responsible for monitoring the wind speed, wind direction, temperature, and relative humidity. The gathered information about the weather will be displayed on a LCD for easy reading and monitoring.
General Information
Power: The weather station is to be powered by a standard wall transformer, with input of 120VAC and output of 5Vdc at 400mA of current.
Microprocessor: XC68HC912B32.
Crystal: A 16MHz crystal is to be connected between EXTAL and XTAL pins.
PortS: Will not be used.
PortE: will not be used.
PortT: Pins PT0, PT1 will be used for two pushbuttons, and PT3 will be connected to Anemometer.
PORTAD: PAD0 will be connected to the weather vane. PAD1 will be connected to the temperature sensor. PAD2 will be connected to the humidity sensor.
PORTDLC: Pins PDLC4-PDLC6 connected to the control pins of the LCD.
PORTA: Pins PA0-PA7 will be connected to the data lines of the LCD.
PORTP: Pins PP4-PP7 are to be connected to the address lines of the RTC.
PORTB: Pins PB0-PB7 will be connected to the data lines of the RTC.
A MC3416P3 low voltage sensor will monitor the power supply. When the MC3416P3 falls below the low voltage level a reset signal will be sent to the MC68HC and RTC.
Project Hardware:
The weather station will include four major pieces of hardware. The four major pieces of hardware include a wind sensor, RH (relative humidity) sensor, a temperature sensor, and user interface.
Wind Sensor
For the wind sensor I will be using the Davis Instrument standard anemometer part #7911. This wind sensor will includes both a weather vane and anemometer. The weather vane consists of a 20k-ohm pot connecting between ground and 5v. This configuration will allow for a voltage between 0 and 5v to be supplied to the A-to-D converter on the 68HC12. Software will then be used to convert this reading to the appropriate direction the wind is coming from. The wind direction will have a display resolution of 8 points (45) with accuracy of ± 7%. The second part of the wind sensor is the anemometer. The anemometer uses a magnetic switch to measure the wind speed. As the anemometer spins it close the switch momentarily spending out a pulse. The number of pulses measured over the sample period of 2.25 seconds is equal to the speed of the wind in MPH. The pulse accumulator pin PT3 will measure the pulse count.
Relative Humidity Sensor
The humidity sensor that will be used is the Honeywell HIH-3610-001 Humidity sensor. The HIH-3610 series delivers instrumentation–quality RH sensing performance in a SIP. The RH sensor is a laser trimmed thermoset ploymer capactive sensing element with on-chip integrated signal conditioning. The sensor has an RH accuracy of ± 2% over a range of 0-100%. The RH sensor will be connected directly input to the A-to-D converter on the 68HC12. The humidity
sensor will be power by the 5v-power supply.
Temperature Sensor
For the temperature sensor I will be using the national semiconductor part number LM335. The LM335 has the ability to operate between –40C to 100C, with accuracy of ± 5%. The LM355 will be supplied by the 5v-power supply through a 2k-ohm resistor. The resistor and LM335 make a voltage divider. The voltage drop across the LM335 is directly related the temperature. The voltage measured across the LM335 will be sent to the A-to-D converter on the 68HC12. Software will then be used to calculate the temperature due to the voltage Drop of the LM335
User interface
The user interface will consist of a LCD and two pushbuttons. The LCD will be used to display the weather data, and the pushbuttons used to scroll through the display.
Real Time Clock (RTC)
The RTC to be used in the product will be the Benchmarq BQ4847 IC. This particular RTC is packaged with its own backup battery and crystal. The RTC has 4-bit address in and 8-bit data input/output port. The four address lines will be attached to general I/O lines on PortP. The eight data will be attached to PortB. The address inputs lines allow access to the 16 bytes of realtime clock and control registers. The data input/output line provides data for the real time clock information.
Pushbuttons
The user interface will include two pushbuttons. These two pushbuttons will be SPST momentary on. The two pushbuttons will be connected to PortT pins PT0 and PT1, using the internal pull-up resistors to eliminate de-bounce. SW1 will be used to scroll through the sensor data. SW2 will be used to display the date and time from the real time clock.
LCD
The LCD display will be a standard 2x16 LCD. Vss will be connected to ground and Vcc will be connected to 5v-power supply. A 20k-ohm resistor connected between Vee and Vcc to provide a contrast for the LCD. Enable, Read/Write, and Reseat, will be connected to PDLC6-PDLC4 respectively. DB0-DB7 on LCD connected to PA0-PA7 respectively.
Item / Quantity / Description / Designators1 / 1 / IC Low Voltage Mon. MC34164P3 / U3
2 / 1 / IC RTC BQ4847 / U2
3 / 4 / Cap Elec. 10% .1uf/50v / C3,C4,C5,C6
4 / 2 / Cap Mono 10% 24pF/50v / C1,C2
5 / 1 / Xtal, 16MHz / X1
6 / 2 / Jack, 6P4C top flange / J2, J1
7 / 1 / Pot 1/2watt Single turn 20kohm / R1
8 / 1 / LCD 2x16, serial, character / DSP1
9 / 2 / push-button, SPST, mom on / SW1, SW2
10 / 1 / Header, .1” 6 contacts / J1
11 / 1 / Hum Sensor, HIH-3610 / SNS1
12 / 1 / Diode, LM335 / D1
13 / 1 / Anemometer, #7911 / SNS2
14 / 1 / Res. ¼ watt 2Kohm / R3
15 / 1 / 1C, 6812, uP, DIP 100pins / U1
16 / 1 / Res. ¼ watt 10Mohm / R1
17 / 1 / Power Supply 120VAC in, 5VDC out / Power Supply
18 / 1 / Enclosure, 9/16 by 1 3/8 by
2 1/8 / Case 1
19 / 1 / Enclosure, 1.5 by 3.2 by 5.6 / Case 2
20 / 1 / Cable 26AWG, 6’ long / Cable 1