This is a very simple analog-to-digital converter circuit based on the 8-bit analog-to-digital converter ADC0808. Typically, an analog-to-digital converter (A/D converter/ADC) needs to be interfaced through a microprocessor to convert analog information into a digital format. This requires additional hardware and appropriate software, resulting in more complexity and overall cost.

The analog-to-digital converter circuit shown here is configured around the ADC0808, getting rid of the use of a microprocessor. The ADC0808 is definitely an 8-bit A/D converter with data output lines D0-D7. It works by successive approximation. It has a total of eight analog input channels, any of which can be selected for use with address lines A, B, and C. Here, in this case, the input channel IN0 is selected by grounding the A, B and C address lines.

Typically, the control signals ALE (Address Latch Enable), EOC (End of Conversion), OE (Output Enable) and SC (Start of Conversion) are connected through the microprocessor. even so,

The circuit shown here can also be run in continuous mode without the use of any microprocessor. Therefore, the input control signals ALE and OE become active high and are connected to Vcc (+5 volts). The input control signal SC goes active low to initiate a conversion on the falling edge of the pulse, while the output signal EOC goes high after the conversion (digitization) is complete. This EOC output is coupled to the SC input, where the falling edge of the EOC output is used as the SC input to instruct the ADC to start subsequent conversions.

The EOC signal goes high as the conversion begins. At the next clock pulse the EOC output goes low again, so SC is enabled to start the next conversion. Therefore, it provides a continuous 8-bit digital output corresponding to the instantaneous value of the analog input. The optimum level of the analog input voltage should be appropriately scaled below the positive reference (+5V) level.

The ADC0808 IC requires a clock signal of typically 550 kHz, which can simply be generated by an astable multivibrator constructed using a 7404 inverting gate. To visualize the digital output, a row of eight LEDs (LED1 to LED8) is used, where each LED is connected to its own data output line D0 to D7. Considering that the A/D converter operates in continuous mode, once the analog input is applied, it will display the digital output. The decimal equivalent digital output value D of the supplied analog input voltage Vin can be calculated from the following relation:

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