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How to interface LDR with ADC0808 using interrupt clock from 8051 microcontroller (AT89C51)


Developed By: 
Himanshu Choudhary

This circuit demonstrates the principle and operation of interfacing an LDR with ADC0808 using the controller AT89C51. This is an 8 channel ADC i.e., it can take eight input signals. The output is displayed on the LCD.


Interfacing ADC0808 with LDR using 8051 Microcontroller Interrupt Clock



ADC0808 is an 8-bit resolution IC with eight input pins. LDR is used to provide the analog input. The output of the LDR is displayed on a 16x2 LCD.  A clock of frequency 500 KHz is generated using Timer0 in the interrupt mode. To enable the interrupt, the value of the register IE is set to 0x82 (Refer interfacing ADC 0808 with interrupt clock).
The output pins of ADC are connected to the port P0 of the AT89C51. The pin10 of the ADC is connected to pin8 (P1.7) of the controller for clock input. ALE, pin22 of the ADC is connected to pin1 (P1.0) of controller. OE, pin9 of the ADC is connected to pin4 (P1.3) of controller. SC, pin6 of the ADC is connected to pin2 (P1.1) of the controller. EOC, pin number 7 is connected to pin 3 (P1.2) of controller. Selector pins A (25), B (24) and C (24) of ADC are connected to the pins 4, 5 and 6 of the controller respectively.
Port P2 (pins 21-28) of controller is used to send the data to the LCD (pins 7-14). RS (pin4) of LCD is connected to P3.0 (pin 10) of controller. R/W (pin5) of LCD is connected to P3.1 (pin11) of the controller. Enable pin, EN, pin6 of LCD will connect to P3.6 of controller (Refer LCD interfacing).
The controller continuously monitors the output of the ADC. The output of the LDR varies with the intensity of light. The value ADC output varies from 0 to 255. The output of ADC is converted to decimal form and then displayed on the LCD (Refer displaying number on LCD). If the output of any of the LDR varies, the corresponding change is reflected on LCD screen.



Circuit Diagram



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