Oscilloscope is quite a universal instrument which I would recommend to invest first. Normal bench scope does the job pretty well. I am not a big fan of DIY scopes that are built of microcontroller and LCD or interfaced to PC via the serial interface. You will never get decent sampling and functionality with low-end parts. But in other hand, building such scope can be fun and be a good choice for student projects. prem_ranjan shares his Arduino-based scope project, where he outputs waveform to MATLAB plots.
The investment into this project is minimal. O course you could capture signal directly to Arduino analog pin, but op-amp based signal conditioning could make life easier. In the end, here are few features of this scope:
- No additional hardware is needed for essential functions;
- max plotted frequency 7kHz;
- up to four channels, max 7/4 kHz each;
- 8-bit resolution;
- variable trigger on channel 0;
- sampling memory is only limited by computer.