Been typing some code, the guys in the yahoo group for spectrometry have a MS windows program to display spectra with the PMT connected to the PC soundcard.
So, as I burned that MS disk, I wrote some Linux code.
The interface is really simple, just an emitter follower from the PMT anode (cathode is at -1284 V in this test): +9V 470n |-----||------- c | PMT anode |-------||----------------------------- b NPN /// | 4n7 | e BC547-B 10 m screened audio cable 1k 3M9 |----------------------------===============//============== PC soundcard mike input | | 1k /// +9 - 100k ---- 100k --| | | /// ///
Why these values? That is sort of what came up when I grabbed in the box. It is always an art to make something with what you get :-)
Anyways, this was a first test, to see what the pulses would look like. I added the scope display as I had no clue (tm) what was going on IN that soundcard, and to write the rest of the soft I needed this. This was still the old xy plot version with only 256 points (for 8 bits via RS232).
See how nice the pulse gets stretched, and even keeps polarity (negative at the anode). That spectrum is bogus, just background from a large BGO crystal for testing.
After typing some more code adding features, one of the things I added is the yellow line in the scope display, that is the slice level for the pulses, also this shows it at 10 x gain (150 mVpp fsd). I did not need the mike boost on the soundcard, just mike slider full open.it is again the same background, but now using the full 16 bits from the soundcard, so more resolution, not that BGO has that. The 'blankout level', is set just above the thermal?? noise. remember without the crystal the line is flat (no signal) no PMT noise, all light flashes.
If anybody is interested in the source code, they should ask here. This code will probably change constantly anyways... Oh, the above thing runs from a 9 V battery... of course it should be build in somewhere, it now sits an a piece of A4 paper on the table.
So that was the coding exercise for today. We can write anything you want in Jan Panteltje's restaurant.