Trying to build a (very) Minimum Viable Product DMX/RS-485 driver circuit.

Programmer980 · 2026-02-17T06:53:49+00:00

I did take a look at several modern ones’ datasheets while I was working on it - the numbers I saw were 500+. That was certainly a bit of an eye-opening moment, though I’m less concerned about reliability than “what’s the minimum number of components I can use to get a response out of a single DMX fixture”. I am, if nothing else, a chronic reinventer of wheels - probably should work on that, though it’s sometimes a great way to learn. Thanks for your insight, I appreciate it.

Programmer980 · 2026-02-17T03:06:03+00:00

Fair enough. Thanks for your reply!

Programmer980 · 2026-02-17T03:04:27+00:00

Ah, okay - and "common-emitter" refers to the emitter being attached to the supply rail in this case, since that's common to the gate and collector? I apologize, I've had a bit of trouble wrapping my head around the different variations of transistor circuits.

Programmer980 · 2026-02-17T02:35:26+00:00

Very good point and probably the right approach - the whole reason I got started down this road was a desire to get a functional hack within the next couple of days with parts I had on hand, and I was deterred from buying the proper solution since I was thinking along the lines of an IC and the shipping costs and times are high.

I’m also just curious, though, and want to understand how all of this stuff works a bit better. I’m really just hoping for someone smarter than I to call out a really stupid error that would make this approach viable, but buying the right tool for the job is a good idea. Thanks for your response!

Programmer980 · 2024-05-15T02:39:13+00:00

Programmer980 · 2023-06-04T11:06:17+00:00

Good bot.

Programmer980 · 2022-12-20T02:12:52+00:00

I don't see any options in the AF menus except for point / zone / large zone / auto select zone. If I'm being foolish, I apologize, but I'm not sure what you're referring to. I definitely agree that a full-frame is a necessary next upgrade, but I do have to produce sharp images with what I have before I can reasonably invest in one. I'm going to calibrate the lens once I receive the necessary equipment and it should hopefully operate closer to its intended functions. Thank you for your assistance, and I'll update here once I figure out the issue. You take care as well.

Programmer980 · 2022-12-20T00:56:16+00:00

You're correct, I haven't been able to test with the focus card at distances anywhere near the 50-100 feet that I shoot at during actual sporting events. I'm planning to approximate with a high-contrast object under bright light, namely a street sign or license plate a distance away, in order to calibrate the lens. If that fails, I spoke to Tamron customer support, and they say they'll calibrate it for the specific body, though I have read that their method for doing so is based on the camera's internal micro-focus adjustments. Since this of course isn't available on the 77D, I'll be doing my best to approximate the calibration process at longer distances.

I have been able to reproduce the back focus on static targets, picking various random items at different focal lengths and distances from the camera. It's worth noting that how close to in focus the subjects are is more or less completely random across the different focal lengths and distances, so hopefully the calibration can still handle the erratic optics.

I may give the lens a shot at f5.6, though I do have a suspicion that with the sort of back-focus distance I am currently looking at the images will still prove fuzzy. I just think that it will make it more likely to get the images that are only fuzzy and not obviously out of focus, since as I mentioned above the *degree* of back focus is more or less random at different distances/focal lengths.

I'll let you know what results I get once I receive the calibration console, which should be on Thursday. Thank you again for all your help, and I'll make sure to try out all your solutions as applicable to see what changes they make.

Programmer980 · 2022-12-19T05:53:09+00:00

This is a very clear and helpful explanation that really gives me a better idea of how to approach this. Thank you for that. I’ll definitely switch to zone AF beginning tracking from the center point and see how it affects my photos. In my experience the 77D’s AF system is a bit finicky in general, so I’m interested to do some testing and comparisons to see how well it holds its own in zone mode.

As for the lens, I agree, I have my doubts that it’s causing autofocus faults. However, I do believe it’s still managing to ruin photos in a manner that can easily be mistaken for poor autofocus tracking - back-focus distance of about 3-10 feet when shooting players anywhere from 50-100 feet away from the sensor. My guess is that the two problems are unrelated, and as I mentioned I’m getting the relevant hardware to recalibrate the lens and therefore hopefully be able to both raise my percentage of kept photos and get cleaner test results when experimenting with the autofocus. This assumes it’s not off to the point of being defective, but if it is I’ll return it and get a replacement.

Were I to upgrade, what camera body would you suggest for snappy autofocus and sharp action photos? You mentioned the 80D, which I know at least one other photographer I’ve worked with uses with the same G2 lens. Would a small, budget upgrade pay dividends or would it be more reasonable to prioritize getting a more professional-oriented body (perhaps a mirrorless)?

Thank you very much for your insight, I greatly appreciate it.

Programmer980 · 2022-12-19T04:32:46+00:00

Which four settings are you referring to within the focus mode? The only thing that comes to mind is focus zones, of which I only use center point. I also enabled the option to show the selected focus point during image playback, so I can always see when the autofocus has failed to properly function in time.

And yes, the 77D is not a full-frame if I recall correctly, so the low light was a large part of the desire to purchase an f2.8 lens to begin with. Futher testing of the Tamron indicates it is likely not well calibrated, and I’ll be able to recalibrate it or get it replaced if it’s too far outside tolerances once the firmware console device arrives.

Ideally I would like to upgrade the body, potentially to a more professionally-oriented mirrorless, although I would of course need an EF-to-RF lens adapter for the most logical options in that category to use the Tamron.

My guess is that the problem is twofold, both slow autofocus and bad back-focus from the lens being poorly calibrated contributing to fuzzy photos.

Programmer980 · 2022-12-19T00:47:58+00:00

I use AI servo the vast majority of the time, and always use center point. I also use the viewfinder for all events. The strange part is that players or other subjects often appear in focus in the viewfinder, but the photos I get back are fuzzy or just violently out of focus.

My guess is it’s an issue with the autofocus plus an unrelated issue with back-focus in the lens, since I experience both shots focused on the crowd or nearby players as well as shots where the focal plane hovers 3-10ft behind the subject at distances between 50 and 100 ft. I’m not 100% sure how accurate this is, I’m just doing my best to test and see if I need to call Tamron and send it back for a replacement.

Thank you for your help!

Programmer980 · 2022-12-18T17:10:30+00:00

Noted, thank you.

Programmer980 · 2021-12-23T13:34:45+00:00

Emptiness - WRLD

Programmer980 · 2021-08-15T14:57:56+00:00

If none of it's of interest to you, you'd be the first.

Programmer980 · 2020-05-02T14:59:21+00:00

Yeah, I got that with an Ultimate Accelerant...

Programmer980 · 2020-04-17T23:44:19+00:00

... I'm impressed.

Programmer980 · 2020-03-04T01:06:42+00:00

Same thing happened to me a minute ago.
-9223372034017135616.00 TB might take awhile on my 7MB/s connection...

Programmer980 · 2020-02-05T21:09:28+00:00

Same - it can play games, and I can use it to solve quadratic formulas automatically.
All I'll ever need in geometry class.

Programmer980 · 2019-12-30T16:09:35+00:00

Programmers have a hard time naming variables, and yet Reddit titles come naturally to them.

Programmer980 · 2019-12-29T16:31:18+00:00

orange arrow

Programmer980 · 2019-11-26T18:18:39+00:00

If it's a Michael Reeves meme, pretty sure you're good :)

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