INTRODUCTION:

The overall objective of this Experiment is to familiarize the equipment and ADC devices.

The Pic 16C711 would be configured as an ADC and interfaced with the computer

Other components necessary include resistors of varies values and capacitors.

The equipment needed for the experiment is shown below.

DESCRIPTION:

Figure 2. Michael’s Oscope Block Diagram

     The different stages are described in the following outline: 

·        Input Buffer: This component has two functions. The first function is to divide the voltage so the sample and hold op-amp does not go to saturation. When the signal enters the system, there is a resistor that opposes more than 20mA, and is divided by two zener diodes that only allow 2.4V peek to peek into the system. The capacitor separates the dc from the ac and the frequency response is 50Hz. The last two resistors act as an offset. This offset is very important for the op-amp is being supplied by a single power supply.

·        Sample & Hold: The sample and hold is for creating a smooth transition from an analog signal to discrete digital signal. The PIC RA3 controls the sample analog switch. Also the specification from the micro controller calls for a sample and hold circuit so the conversion can operate efficiently.    

·        ADC & Sampling triggering: The 16C711 micro controller controls the ADC and the sampling triggering. The first function that turns on when the micro controller is powered on is the sampling function. The pulse width of the sampling is controlled by the speed of the micro controller. The speed of the micro controller is two megahertz and this speed also affects the analog to digital converter as well. The second function turns off the sampling and starts the ADC. When the ADC complete flag turns on then the information is stored in an eight-bit resister. The last function before heading out to the computer is the eight-bit to four-bit conversion, which truncates the eight bit to four bit making a low resolution.   

·        Computer Interfacing: When the computer receives the information, the program stores three thousand entries. Then the information is distributed to a graph. Where it is ploted to a voltage verses time graph. The program is EXCEL with micros or with visual basic. The program is simple. When the user clicks the start button the program records the information from the parallel port and graphs it to the voltage vs time chart. The back draw from this simple program is that the refreshing of the graph takes a long time. The only way to speed up the process is to have a faster processor or the program is done on visual C++.