DPScope - Build Your Own USB/PC-Based Oscilloscope

Step 3 Design Overview

Below is a block diagram of the oscilloscope. The architecture is fairly traditional; the input signals are conditioned in the analog frontend which depending on the signal levels either attenuates them or amplifies them, and can also add offset. All this is necessary to make optimum use of the fixed voltage range that the analog-to-digital converters can convert into digital information.

The analog-to-digital converters (ADCs) take the analog signals and convert them into digital numbers. The sample logic controls the sampling process and the storage of the converted data in the capture memory. The trigger circuitry decides when to start the sample process.

The controller takes care of setting signal gains and offset, setting up the sample logic, selecting trigger source, trigger level, and trigger polarity, and communicating the the PC.

As you can see, the dsPIC30F2020 microcontroller allows to implement most of it without external circuitry - controller, memory, sample logic, analog-to-digital converter (ADC), trigger and trigger level control all reside within a single chip. This makes the design very compact, inexpensive, and easy to build.

USB interface to the PC as well as power supply for the scope are provided by the FTDI232R serial-to-USB converter cable - again a very user-friendly solution since there is nothing to assemble.