Periodic noise on BNC and TPs, no signal

[JMulder99]

Hi, My detector worked in the past (expected detection rate), but currently it does not count any signal. The BNC (direct from the SiPM) and all TPs show a periodic tick that is overlayed on top of the peak from the muon passing through. Here is a picture of the oscilloscope showing the BNC (yellow) and TP3 (blue). As you can see, the periodic noise even goes through the peak detector.

Have you seen this periodic noise before and why are the muons not counted while a peak is detected (eventhough its being overlayed with a periodic noise signal)?

[spenceraxani]

Hi,

The periodic noise appears to have a 300ns period, indicating that this is due to the switching frequency of the 3MHz DC-DC booster. I also see this noise, however, it will not affect the function of the detector. To clarify, TP3 is 50Ohm terminated, correct? TP3 should decay over ~ms scales, rather than few us scales. But if you are terminating the input to the oscilloscope to 50Ohms, this will cause it quickly to decay away. Perhaps this is why the detector isn’t counting any signals?

Another possibility is that the detector isn’t seeing the waveform drop below the RESET_THRESHOLD variable. You can try raising the value of this variable.

Thanks,

Spencer

On Jun 29, 2022, at 12:00 PM, Jelmer Mulder @.***> wrote:

Hi, My detector worked in the past (expected detection rate), but currently it does not count any signal. The BNC (direct from the SiPM) and all TPs show a periodic tick that is overlayed on top of the peak from the muon passing through. Here is a picture of the oscilloscope showing the BNC (yellow) and TP3 (blue). As you can see, the periodic noise even goes through the peak detector.

https://user-images.githubusercontent.com/52777149/176481338-8e894c83-1d9b-48a9-96e9-f2bc55170165.jpg Have you seen this periodic noise before and why are the muons not counted while a peak is detected (eventhough its being overlayed with a periodic noise signal)?

— Reply to this email directly, view it on GitHub https://github.com/spenceraxani/CosmicWatch-Desktop-Muon-Detector-v2/issues/90, or unsubscribe https://github.com/notifications/unsubscribe-auth/AANF5O3HVYIKTXRTCD2VUBTVRRXJPANCNFSM52GI4E2Q. You are receiving this because you are subscribed to this thread.

[JMulder99]

Do I need to replace the DC-DC booster to get rid of the noise?

The oscilloscope (attached to TP3) is indeed set to 50 mVΩ. I don't see how the fading away on the oscilloscope would influence the triggering on the board. The board also does not count any when the oscilloscope is not attached. I will try setting the threshold lower.

[spenceraxani]

It looks worse than what I normally see, although I would not replace it. It won’t affect the detector in any way besides looking a bit messy on the scope.

TP3 is the probing the peak detector output. It works by charging a capacitor that bleeds away through a ~200kOhm resistor to ground. When you terminate TP3 with a 50Ohm connection, you are essentially placing a 50Ohm in parallel with the 200k resistor, which changes the decay of the pulse proportionally.

Since the detector is not counting when the scope is disconnected, my bet is that the threshold fixes the issue. I ran into this problem 4 times in the last few months. I think it may be related to a DC offset on the ADC of some newly manufactured Arduino Nanos. In the Arduino code, there’s a line "while(analogRead(A0) > RESET_THRESHOLD){continue;}” you could have this loop print out something to confirm that it is getting stuck in this loop. That would conclusively tell you that this is the problem.

Spencer

On Jun 29, 2022, at 2:26 PM, Jelmer Mulder @.***> wrote:

Do I need to replace the DC-DC booster to get rid of the noise?

The oscilloscope (attached to TP3) is indeed set to 50 mVΩ. I don't see how the fading away on the oscilloscope would influence the triggering on the board. The board also does not count any when the oscilloscope is not attached. I will try setting the threshold lower.

— Reply to this email directly, view it on GitHub https://github.com/spenceraxani/CosmicWatch-Desktop-Muon-Detector-v2/issues/90#issuecomment-1170344348, or unsubscribe https://github.com/notifications/unsubscribe-auth/AANF5OZDFYNZSO3GXTB2MIDVRSIOTANCNFSM52GI4E2Q. You are receiving this because you commented.