A Multi-Parameter Water Quality Monitoring System Using 8086 Microcontroller and ADC0808

System Architecture:

• Uses sensors (Temperature, pH, Turbidity, DO) to measure water quality.

• Employs an ADC0808 to convert analog sensor signals to digital.

• Uses an 8051 microcontroller (AT89C51) to process and display data.

• Drives 7-segment displays using MAX7219.

• Triggers alerts using comparators (LM339), LEDs, and buzzers if readings are out of safe range.

Detailed Flow

1. Sensors & Signal Conditioning

Each sensor is connected through a voltage divider (variable resistor for calibration):

• RV1 + LM35 → Temperature sensor

• RV2 + pH Sensor → pH level

• RV3 + Turbidity Sensor

• RV4 + DO Sensor

These output analog voltages proportional to the measured parameters.

2. Analog Multiplexer (U2 - ADC0808)

• Accepts 8 analog input channels (A0–A7).

• Converts selected analog signal to digital using 8-bit resolution.

• Controlled via select lines (A, B, C) from the microcontroller.

• OE, START, EOC, and ALE are control signals for synchronization.

3. 8086 Microcontroller (U1)

• Central processor that:

  • Selects ADC channel.

  • Starts conversion.

  • Waits for EOC (End of Conversion).

  • Reads converted 8-bit value.

  • Sends data to display.

  • Checks thresholds and activates alarms.

4. Display Driver (U3, U40 - MAX7219)

• MAX7219 takes SPI input from 8051 and drives 7-segment displays.

• 4-digit 7-segment display used for each parameter.

• Each parameter has its own MAX7219 driving it (DIG0–DIG3).

5. Alarms (Comparators + LEDs + Buzzers)

• LM339 quad comparator is used for each parameter.

• Receives:

  • One input from sensor signal (via voltage divider).

  • One input from reference voltage (threshold).

• If the sensor value exceeds the reference:

  • Comparator output goes HIGH.

  • Drives RED LED + BUZZER for that parameter.

  • Activates corresponding alert signal to microcontroller.

• Alerts:

  • ALERT_TEMPERATURE

• ALERT_PH

  • ALERT_TURBIDITY

• ALERT_DO

6. Multiplexing & Control Logic

• 74LS373, 74LS573, 74LS138 (U4, U5, U8, U9, U11) handle:

  • Data/address multiplexing.

  • Output enable control.

  • Chip selection.

• Used to expand addressable memory/data lines for the 8051.

7. Control Logic for Timing (U6, U7)

• NOR gates combine control signals:

  • Ensure correct timing between ADC START, WR, ALE signals.

  • Avoid data corruption during ADC reading.

Displays

7-Segment LEDs

• 4 separate sections showing:

  • Temperature – LM35 (display in °C)

  • pH – pH Sensor (0–14 scale)

  • Turbidity – in NTU (Nephelometric Turbidity Units)

  • Dissolved Oxygen – in mg/L

• Each has:

  • 4-digit display

  • Green/Red LED based on safety range

  • Buzzer for alert

  • Safe range labeled for reference

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Threshold Values and Alert Conditions

Parameter	Safe Range	Alert Condition	Signal
Temperature	15–35°C	<15 or >35 triggers alert	ALERT_TEMPERATURE
pH	6.5–8.5	Outside this range	ALERT_PH
Turbidity	0–50 NTU	>50 triggers alert	ALERT_TURBIDITY
Dissolved Oxygen	>5 mg/L	<5 triggers alert	ALERT_D -