0.2 ms is equivalent to a max. sample rate of 5 kHz, not taking into account the time in between samples the program needs to perform calculations, store data etc.
So usable maybe 2 kHz to 3 kHz sample rate, depending on the program.
According to the
Nyquist-Shannon sampling theorem the sample rate needs to be at least 2 × f
max, i.e. twice as high as the maximum signal frequency to be able to reconstruct the signal. Since you obviously do not perform any form of advanced filtering to reconstruct the signal from the samples, this factor goes up to maybe 10 times or 16 times. In other words, the max. signal frequency that can be usefully displayed by your simple algorithm (although I admit I'm working on assumptions here as you haven't published your program) is at lkeast 10 times less than the max. sample rate. This amounts to approx. 200 Hz ... 400 Hz.
One simple method to improve the visual display is to draw small line segments between the dots instead of drawing the dots alone. The Basic interpreter of your computer surely has instructions for that.
Drawing lines takes time, however, so I suggest you separate acquiring data and displaying data into two steps:
- loop 1: acquire data for 1 screen
- loop 2: display acquired data drawing lines between points