I was not satisfied with the resolution that the monochromator gave me, so I redesigned it. The main problem with the fist setup was, it was using a hobby servo motor, which resolution was 1 degree.

The diffraction grating effective movement which gave me the spectrum from ~400nm to  ~700nm was 18 degrees, so for 300nm wavelength I got 18 steps. The first version of course worked and maybe easier was to build, but the wavelength resolution was simply not enough for me.

For the second designe I have designed it with a stepper motor, which I had laying around. That motor resolution without micro stepping was 0.9 degree, but for better resolution I used 1/8 micro stepping. With 1/8 micro stepping I have got ~0,1125 degree pecision. Before I had 18 steps to cover the full visible wavelength, now I have 120 step.

I have also uploaded these designes to my thingiverse, you can download them.

The new designe:

The grating plate stayed the same, but I have printed a tube wich tightly fits to the motor shaft and after just glued the grating flate to it.

The mounting cube got a little bit bigger, because of the morot mounting and the shaft length. Everything stayed the same.

The result is quiet amazed me, how such cheap parts can make that good result (The maximum uploadable file size is 5MB sadly, so I had to compress the gif, it is not the real picture quality, but you got the idea anyway) :

Here is a whale, which I find on an optocoupler IC die: