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ADC0804 Application in AD Conversion Circuit [FAQ]

  • Contents

I. Description

The role of analog-to-digital conversion (AD) is to convert continuous analog quantities into discrete digital quantities through sampling. It is widely used in circuit design, such as the digitization of analog quantities such as image, voltage, and current. The function of the AD chip is to complete the analog-to-digital conversion function. There are many kinds of AD chips. This article takes ADC0804 as an example to elaborate on the software and hardware design methods of the AD conversion circuit.

ADC0804

Catalog

I. Description

II. ADC0804 Introduction

III. Circuit Connection Diagram

IV. ADC08904 Timing Analysis

4.1 ADC08904 Start Conversion Timing Analysis

4.2 ADC0804 Read Data Timing Analysis

V. ADC0804 Analog-to-digital Conversion Test Program

VI. Conclusion

FAQ

Ordering & Quantity

II. ADC0804 Introduction

ADC0804 is a step-by-step comparison AD converter, using CMOS manufacturing process, 20 pins, 8-bit resolution, the input analog voltage range is 0-5V, and the typical conversion time is 100us. The chip contains a three-state data output latch, which can be directly hung on the data bus of the microcontroller.

 

III. Circuit Connection Diagram

Figure 1 Circuit connection diagram

Figure 1 Circuit connection diagram

The circuit connection diagram is shown in Figure 1 above, which mainly includes AT89S52 single-chip microcomputer, ADC0804, and 8 light-emitting diodes. The 31-pin of the one-chip computer is connected to the high level, the purpose is to make the one-chip computer start to execute the program from the internal ROM after power-on.

 

The following focuses on the peripheral circuit design of the ADC0804 chip and the connection between the corresponding pins and the microcontroller. The 20th pin of ADC0804  is connected to 5V for powering itself, and pin 0 is the power ground. Pins 11-18 are the converted digital signal output terminals, which are respectively connected to P1.7-P1.0 of the single-chip microcomputer and connected to the anodes of 8 light-emitting diodes (LED1-LED8). The function of connecting the light-emitting diode is to intuitively test the correctness of the circuit design and programming by observing the change of its on-off state. The details will be given later.

 

Pin 1 CS is the chip selection terminal, connected to pin P3.5 of the microcontroller, and the low level is active. Once CS is active,  ADC0804  is ready to start working immediately. Pin 2 RD is the read signal input terminal, connected to pin P3.7 of the single-chip microcomputer, low level is effective. 3 pin WR is the write signal input terminal, connected to the single-chip P3.6 pin, the low level is valid, and the WR is valid, the AD conversion is started immediately. The 19-pin CLKR is the external resistance end of the internal clock generator. The RC oscillator circuit is formed by a 10K resistor and a 150pf capacitor. The oscillation signal output by the oscillator circuit is connected to the 4-pin CLKIN as the clock pulse of ADC0804,  The pulse frequency is 1/( 1.1R*C), if the capacitor is selected too much, the conversion rate will be affected.

 

Pin 5 INTR is the interrupt signal output terminal. When it outputs a low level, it indicates the end of AD conversion and prompts the controller to do the corresponding processing. This article does not use the interrupt mode, so the pin is left floating. 6-pin VIN+ and 7-pin VIN- form a pair of analog differential signal input terminals. Among them, pin 6 VIN+ is connected to an adjustable resistor through a 10K current limiting resistor. By adjusting the size of the adjustable resistor, a voltage between 0-5V can be obtained. Since pin 7 VIN- is grounded, the voltage is It is the analog input voltage of ADC0804. The task of  ADC0804 is to convert the analog voltage into an 8-bit digital quantity, the range is 0x00-0xFF. Pin 9 VREF/2 is the reference voltage input terminal. The reference voltage is 2.5V, which is obtained by dividing the 5V voltage through two 1K resistors.

 

IV. ADC08904 Timing Analysis

4.1 ADC08904 Start Conversion Timing Analysis

Figure 2 ADC08904 start conversion timing diagram

Figure 2 ADC08904 start conversion timing diagram

 

According to the ADC0804 start conversion timing diagram (Figure 2), it can be seen that the ADC0804 starts the conversion through the following series of processes: first, clear CS, that is, change CS to a low level, after a slight delay, change WR from high level to low level, and then change WR to a high level after a slight delay, and the AD conversion is officially started. After 1-8 AD conversion time periods, the analog-to-digital conversion is completed, and the conversion result is automatically stored in the internal latch. At the same time, the INTR interrupt output terminal becomes low level to inform the  MCU  of this AD conversion junction, and the  MCU then takes out the data by reading for subsequent processing.

 

4.2 ADC0804 Read Data Timing Analysis

Figure 3 ADC0804 read data timing diagram

Figure 3 ADC0804 read data timing diagram

 

According to the ADC0804 read data timing diagram (Figure 3), it can be seen that the ADC0804 read data operation needs to go through the following series of processes: first clear CS, that is, CS becomes low, and after a slight delay, RD changes from high to high Low level, after Tacc time, the data on the digital signal output terminal (digital signal after A/D conversion) can be stabilized. At this time, the microcontroller can read the data on the digital signal output terminal, and then pull RD to a high level.

 

V. ADC0804 Analog-to-digital Conversion Test Program

This article writes a complete ADC0804 analog-to-digital conversion test program, as shown below, and gives the program function comments line by line. The program is written strictly in accordance with the ADC0804 start-up conversion timing and read data timing. Its function is to obtain different voltages by adjusting the adjustable resistor R2 in Figure 1. This voltage is used as the analog input of ADC0804.  which is converted to 8-bit digital quantity by ADC0804 and drives 8-bit light-emitting diodes respectively. Different voltages are converted into different digital quantities so that the brightness of the 8-bit LED is different. Observing this phenomenon indicates that the design of the analog-to-digital conversion circuit in this article is correct.

 

VI. Conclusion

In this paper, 8051 single-chip microcomputer is used as the controller, the ADC0804-based analog-to-digital conversion circuit is designed, the working principle of ADC0804 is discussed, and a complete test program is given and annotated. Through testing, the circuit can work normally, laying a good foundation for further research in the field of circuit design in the future.


FAQ

  • What is the typical conversion time of ADC0804?

100us

  • What is the function of the AD chip?

Complete the analog-to-digital conversion function

  • What is adc0804?

The ADC0804 is a commonly used ADC module, for projects were an external ADC is required. It is a 20-pin Single channel 8-bit ADC module. Meaning it can measure one ADC value from 0V to 5V and the precision when voltage reference (Vref –pin 9) is +5V is 19.53mV (Step size).

  • What is the difference between adc0804 and max1112?

ADC0804 is used for parallel ADC and MAX1112 is used for serial ADC.

  • Which pin of the adc0804 indicates end of conversion?

PIN-5 – Interrupt (INTR) This pin automatically goes low when conversion is done by ADC0804 or when digital equivalent of analog input is ready.

PIN-6 – Vin (+) connect input analog sensor pin/input voltage to this pin.

  • What is ADC and DAC?

ADC stands for Analog to Digital Converter, which converts the analog signal into the digital signal. DAC stands for Digital to Analog Converter and it converts the Digital signal into an analog signal.

  • What is the resolution of 8 bit ADC?

For example, an ADC with a resolution of 8 bits can encode an analog input to one in 256 different levels (28 = 256). The values can represent the ranges from 0 to 255 (i.e. as unsigned integers) or from −128 to 127 (i.e. as signed integer), depending on the application.

 

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