Automated Pool Maintenance System

Jonathan Arbogast

Janine Garnham

Ajay Suthar

Project Description

Monitors and controls pH and temperature of a swimming pool

Wireless control from a graphical interface on the customer’s PC inside the home

Allows for multiple temperature settings to be entered for different time periods

Home PCRS-232 CableRS-232 Cable

Embedded Controller

Communication Path fromHome PC to the Embedded

Controller

Wireless Modem Wireless Modem

Project Description

Modeling a Pool– Pool is replaced with

a 20 gallon fish tank– Pool pump is

replaced with a small circulation pump

– Heating system is replaced with a hot plate

User Interface

Two screens are available for the user– One main screen for

monitoring and entering new settings

– One screen to schedule different temperature settings

pH Specifications

Recommended pH levels for a pool are 7.2 to 7.8

The system will be able to control the pH level to within ±0.1 pH units

The pH sensor has a sensitivity of 0.02 pH units

Temperature Specifications

The accuracy of the monitored and controlled temperature will be within ±1C when heated

The resolution of the temperature sensor is 0.07 °C with a range between -15 °C and 100°C

Project Components

Fish Tank 2 Temperature

Sensors 1 pH Sensor Hot Plate Acid/Base/Water

Pumps Windows PC HC12 uController Wireless Modems

Temperature

Sensor

Pump

Hot Plate

Component Placement Around the Pool

HC12Controller

Alkaline AdderAcid Adder

pH

Sensor

Temperature

Sensor

Internal Operation

Interface to Sensors/Pumps/Hot Plate HC12 Processing Serial Protocol Wireless Conversion User Inputs

Interfacing to the Sensors

pH sensor has one DC output– Linearly related to the pH level– 1.75V at a pH of 7– 0.25V/pH level change

Temperature sensor has one DC output– Varies linearly with respect to temperature

These voltage levels will be connected to three ADC ports on the HC12

Placement of Temperature Sensors

One sensor placed at the pump output One sensor placed at the other side of the pool Running average will be used

Interfacing to the Pumps

Using simple windshield washer pumps

– Controlled by a 12V signal– Circuit based on a

Darlington Pair will be used to convert the 5V output from the HC12 to a 12V signal with enough drive capability

0

From HC12U 1 A

7 4 3 7

1

23

12

1 2 V

R 1

1 5 0

WasherPump

Q 12 N 2 7 8 5

3

2

14

12

5 V

Interfacing to the Hot Plate

Hot Plate Interface– Crydom AC Relay– Controlled by a 1.6mA 5V signal– Can drive 12A at 120V AC on the output side

HC12 Processing

Must respond to several interrupt sources

– pH Sensor– Temperature Sensors

Must make decisions based on the user’s settings

Must control the hot plate and pumps to satisfy the user’s settings

Serial Protocol

We will use a higher level protocol to check for errors and recover from them

– Uses set start and stop bytes for all messages

– All messages include a checksum

– All messages are either ACKed or NACKed

Serial PortInitialization

Look for StartCharacter (X)

Look for StopCharacter (Y)

Check theChecksum

Send NAK(XNY)

Parse theCommand

Send ACK(XOY)

Wireless Conversion

Conversion to wireless signals is handled by MaxStream modems

Buffering at both the input and output side Translation between RS232 and 5V CMOS is

handled by converter board.

User Inputs

Windows software converts user actions into serial messages

Sent over wireless modem to the HC12 for processing

Software is built using Java

T - Get the current temperatureP - Get the current pH level

S - Set the desired temperatureC - Set the desired pH level

Wireless Demo

Small demo of the wireless communications Modems are setup in a loopback

configuration

System Verification

A “second opinion” must be used to demonstrate that the specs have been met– Temperature checked with a digital thermometer– pH checked with a separate digital pH meter

Future Enhancements

Base/Acid/Water Level Sensors Chlorine Sensors & Dispensers

– Not included due to expense

Adjusting for different pool sizes– Would change the amount of acid/base to add– Would change the temperature response times

Questions??