GPD-3303S rotary knob deboune questions - Page 1
Forum section: electronics / testgear

author: rfdes
author_rank: Regular Contributor
timestamp: May 25, 2021, 09:43:16 am
content: Hi -I've owned my GPD-3303S for about 4 yrs or so and something that has always bothered me was the fact the rotary knobs (when set to the fine tune position) seem to be very finicky (aka debounce) when tuning. The only schematic that I have shows no electrical debounce filtering on the mechanical knob contacts. Therefore, all of the de-bouncing is done in software. I am wondering if others have seen the same debounce issue with their units.The plan is to open the unit and see if I can verify that my rotary knobs are as 'glitchy' as they seem and if so, add some RC filtering of some type. It seems suspicious that the issue appears to be present only when the knob is set to the 'fine tune' mode. I am wondering if maybe the uP DAC programming for fine tuning is borderline flaky giving me the impression that the knob adjustment interpretation is the problem.Curious if anyone has any additional ideas? (firmware update maybe?)Take care -Jim

author: jjoonathan
author_rank: Frequent Contributor
timestamp: May 25, 2021, 02:14:41 pm
content: I had exactly this power supply with exactly this problem and tried exactly this solution, but I couldn't get it to work -- I was able to smooth the voltage waveforms until they appeared squeaky clean on an oscilloscope, but I was never able to get rid of the finnicky / unreliable mapping between knob and displayed number. I didn't chase it further (e.g. it could be a comparator issue or something) but my working hypothesis was that it was due to a poorly implemented acceleration algorithm, a firmware issue.My eventual "solution" was to discard the GPD-3303S and instead buy a GPP-4323, which is the polar opposite: the firmware makes no attempt at acceleration, but it's crisp and responsive (see: 0:38s below).

author: coromonadalix
author_rank: Super Contributor
timestamp: May 25, 2021, 02:19:15 pm
content: it depends if the debouncing is done by software or added components .... or the encoder has oxydation ??

author: rfdes
author_rank: Regular Contributor
timestamp: May 25, 2021, 04:39:49 pm
content: You make a good point about the acceleration algorithm. That may be the issue. However, I seem to notice that if I gently rock the rotary control back and forth, slowly, there are times where the controller misses the count. In my case it may be poor mechanical contacts. Do you know if these are sealed? Hopefully I could add a tiny bit of Deoxit to clean the contacts.

author: rfdes
author_rank: Regular Contributor
timestamp: May 25, 2021, 04:41:34 pm
content: Hi -Thanks... The decoding is definatly software only. The 2-bit rotary contacts are pulled up to Vcc and fed directly into the uP.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: May 25, 2021, 05:31:11 pm
content: I'm afraid I saw the missing-counts-in-fine-adjustment symptom too, even after I had installed a fresh encoder and a RC network that made the waveforms pristine and reliable as seen on an oscilloscope.

author: rfdes
author_rank: Regular Contributor
timestamp: May 26, 2021, 12:26:03 pm
content: Hmmm... OK, I guess that ends that idea. I certainly appreciate the discussion.Take care -Jim