LCS-1M - A Full-Featured, Low-Cost Hobby Oscilloscope

Step 29 Spectrum Analyzer Mode & X-Y-Mode

The picture here shows the same waveform as the previous slide (CH1, square wave), but now in real-time frequency display. Great to find resonances and oscillations and to analyze periodic signals. Basically the scope works as a spectrum analyzer, with no extra hardware. The refresh rate is somewhat slower than in normal mode because of the real-time FFT (Fast Fourier Transformation) the computer has to perform after each acquisition. You can display power or voltage, linear or logarithmic scale, and use several different filter methods (e.g. Hamming).

Based on user suggestions I recently also implemented a X-Y display mode. In this mode, channel 1 provides the horizontal deflection, and channel 2 the vertical deflection. This display mode - well known from classic cathode ray oscilloscopes - provides a good way to e.g. check out
reactive components like capacitors and inductors - one channel looking at the voltage across the component, the other one looking at the current. Or feed in two waves of different frequency and enjoy the resulting Lissajous plots. It is usually easiest to set up levels, trigger etc. in normal mode and then switch into X-Y mode. The sample record should comprise at least one full period of the slower signal, a bit more is even better. A screenshot of this mode is shown below (Lissajous plot of two sine wave, one having twice the frequency of the other).