Oscilloscope


Posted on Feb 6, 2014

For the purpose of this project, digital signals can be communicated with computers while analog signals can`t. RS232 is the name given to your serial port. At the back of your computer, there`s many ports where you can plug things into. The RS232 port has 9 pins and looks like: At the heart of most digital oscilloscopes is a device (usually a chip of some sort) which converts analog


Oscilloscope
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voltage levels to digital signals. This chip is called an analog to digital converter (ADC). If this happens very quickly and the computer keeps track of voltage over time, a plot can be drawn, hence the principal of a digtal oscilloscope. How quickly the chip is able to make these conversions is called the sampling frequency. It is given in units of ksps (kilo-samples per second) or Msps (mega-samples per second). And if you know the sampling frequency to be f, the highest frequency sine wave it can detect is f/2. This is known as the nyquist frequency. Any higher than that and all you`ll get erroneous results and an effect known as aliasing (click here for details). For my case, I chose ADC0804 because they are readily availible at Supremetroncis. This chip is guarenteed to work at 8ksps. And hence, the nyquist frequency is 4kHz. That means, the fastest sine wave I can see with chip is 4kHz before bad things start happening. Most oscilloscopes have some analog circuit which will amplify and shift the trace before it is sampled by the ADC. By shifting the signal before amplifying it gives better accuracy in many cases (avoid saturation with amplifiers). As with all analog circuits, they will work only within a range of frequencies. After a specific frequency, the cut off frequency, the output voltage level is less than 70. 7% of the original voltage level and is considered unsuitable for measurement. It would be...




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