Scopey II: A Simple Scope and Spectrum Analyzer Facing the demise of my Tektronix 2213 in an somebody transport traveling, I featured the mind of either purchase an costly CRT to get it running again, or payment my nights aquatics ebay for other ambit. Having two not so uppercase options, and having conscionable mark with copious amounts of withdraw experience, I definite to upright sort my own. Patch it power not feature the unvaried bandwidth or accuracy of the old Tektronix, it is a accessible lowercase device that I’m trusty will be quite efficacious once I block tinkering with it, and it has several nifty features that a nimiety
The oscilloscope consists of an input stage consisting of a resistive attenuator with 1Mohm impedance, a switch to remove or insert a capacitor for AC or DC coupling, followed by several amplifiers. The first amplifier is a unity gain inverting buffer, followed by a level shifting circuit to center the signal around .5Vcc (2.5V) for the PGA and ADC.
The stage immediately preceding the ADC pin on the dsPIC is a Microchip MCP6S21 PGA (programmable gain amplifier), which is used with gains of 1, 2, 4, 8, 16 and 32 to give gains (attenuation * gain) of 1/8, ¼, ½, 1, 2, and 4, allowing for a wide range of input signals to be visualized. The PGA is connected directly to an ADC pin on the dsPIC.
The Spectrum Analyzer:
The Spectrum Analyzer uses the same input amplifiers as the oscilloscope, although the data format is signed fractional instead of unsigned integer in order to utilize the Microchip DSP libraries. Once acquired, the data is windowed using a Hann window and scaled to prevent overflow in the FFT functions. The data is then transformed to the frequency domain, scaled logarithmically, then displayed. When scaling the data, the bin containing the fundamental is found and the associated frequency is found and displayed in the text portion of the display. Author: Jaime Garnica
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