DU530 CFL Spectra – Again

In my previous post hacking around with the DU530 I showed a spectra from a CFL which matched published spectra. However I was still having a number of issues, particularly with the stepper driver. In particular I was having issues with the stepper skipping steps.

I’ve been using an EasyDriver (clone) and found that if I disabled microstepping everything was working correctly, but when microstepping was enabled steps would be skipped.

I installed a shunt resistor and took a look at the current output on a scope (over the shunt). I used a couple of 0.22Ohm resistors as this is what I had to hand…

The current trace looked like this:

So for some reason it was hitting it’s maximum current output and then just sitting there. I don’t fully understand why, but reducing the current (via the current adjust pot on the board) and increasing the supply voltage (I pushed it to 24, which seems like it’s more than should be required, but still drawing only ~300mA) resolved the issue. I don’t fully understand why the current adjust should have this effect and should probably investigate further. But the traces look fine and I don’t see any missed steps:

With these changes I was again able to resolve the CFL spectra but now I have more freedom with speed/acquisition time…

Acquiring on the scope at a lower speed seems to result in more noise (likely from vibration), but at least a still visible spectra:

This means I can probably move on to acquiring the photodiode output on a microcontroller… a picture of the EasyDriver/shunt is below for reference: