Block Schematic and Function Description
The figure shows the simplified block schematic of the system. For ease of portability the unit is powered and controlled from the USB port of a PC.
A PIC18F14K50 and dsPIC30F4011 microcontrollers are used to provide the functionality of the unit.
The first PIC microcontroller implements the following functions:
· Communicates with the host PC for enumeration as a USB to UART device
· Sets up the unit as a 200mA device
· Switches on power to the DC-DC converter
· Acts as a USB communication interface to the second PIC
The second PIC microcontroller implements the main Oscilloscope Functions
· Analog to Digital conversion of the CH1 & CH2 signal conditioned inputs at the required sampling rates
· Trigger interrupt handling
· Responding to serial commands from PIC1 and sending back the acquired data.
· A Busy signal is also generated
The dual-charge pump circuitry of the MAX232 is used as a DC-DC converter to provide a nominal ± 10V to all the analog circuitry.