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Spectrum Analyzer and Oscilloscope from dsPIC
Scopey II is the name used for this project which involves the use of dsPIC to build an oscilloscope and spectrum analyzer.
The device is using a BNC jack on the front where everything comes in through it followed by attenuation or amplification of the signal. The PIC controls the gain of the input stage which level shifts the input for the reading of the negative voltages to be enabled. The potentiometers located in the front panel as controls are read by the ADC and the graphics LCD displays all the information gathered.
The input stage is a capacitor with a switch. The opening of the switch signifies that the signal must pass through the capacitor which blocks the DC from passing. The DC can only get through if the capacitor is shorted due to the closing of the switch. The signal is being attenuated by a resistive divider by about 1/8 and gives an input impedance of about 1M Ohm.
To create positive and negative DC supplies, a typical center-tapped transformer with full wave rectifier is used while incorporating the standard 3-terminal 7805 for positive and 7905 for negative 5V.