Controller Circuit

The ADC0803 family is a series of three CMOS 8-bit successive approximation A/D converters using a resistive ladder and capacitive array together with an auto-zero comparator. These converters are designed to operate with microprocessor-controlled buses using a minimum of external circuitry. The 3-State output data lines can be connected directly to the data bus. The differential analog voltage input allows for increased common-mode rejection and provides a means to adjust the zero-scale offset. Additionally, the voltage reference input provides a means of encoding small analog voltages to the full 8 bits of resolution.

Circuit figure a digital transducer interface output;


The figure shows an example of digitizing transducer interface output voltage. In this case, the transducer interface is the NE5521, an LVDT (Linear Variable Differential Transformer) Signal Conditioner. The diode at the A/D input is used to insure that the input to the A/D does not go excessively beyond the supply voltage of the A/D. See the NE5521 data sheet for a complete description of the operation of that part.

Circuit Adjustment
To adjust the full scale and zero scale of the A/D, determine the range of voltages that the transducer interface output will take on. Set the LVDT core for null and set the Zero Scale Adjust Potentiometer for a digital output from the A/D of 1000 000. Set the LVDT core for maximum voltage from the interface and set the Full Scale Adjust potentiometer so the A/D output is just barely 1111 1111.