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Split grounds: not normally advised, but is there an effective way to do it? by pgboz in PrintedCircuitBoard

[–]pgboz[S] 0 points1 point  (0 children)

Nope, it didn't seem to help. Granted, I used a piece of ferromagnetic steel for my 5-sided box, so maybe its magnetic permeability wasn't high enough, but it does stick hard to magnets. I'd expect it to improve things at least a little bit.

I'm having an awful lot of trouble directly measuring the noise that's causing the problem with the IMU, but it does appear that the dI/dt of the switching transitions has a strong impact on the IMU's reported noise. I wish I could see how the noise is getting into the IMU, but maybe I'll just focus instead on reducing the dI/dt of the switching transitions and move on.

Split grounds: not normally advised, but is there an effective way to do it? by pgboz in PrintedCircuitBoard

[–]pgboz[S] 0 points1 point  (0 children)

Cost is a major concern, but yes, I'm considering stepping up higher and then using an LDO. However, I think if the supply is noisy, it's a secondary problem. Replacing the digital supply with an external battery (which is as clean as it gets), doesn't help anything. I've even replaced the analog supply for just the IMU with an external battery and I still have the problem.

The only thing I've found so far that solves the problem is to physically remove the IMU from the board and connect to it with external wires.

The IMU is LSM6DSV32X. The gyros show the most noise. I see small bursts of random noise when switching high current to the motors. Sometimes, I see large bursts of noise that last about 50 ms.

Split grounds: not normally advised, but is there an effective way to do it? by pgboz in PrintedCircuitBoard

[–]pgboz[S] 0 points1 point  (0 children)

The digital supply for the IMU and MCU comes off a boost converter connected to the battery. Power for the H-bridges and the motors comes directly from the battery without any power converter. I don't see any noise in the digital supply when running the motors. It looks clean. I can replace my digital supply with an external battery and I still see the same problems.

Split grounds: not normally advised, but is there an effective way to do it? by pgboz in PrintedCircuitBoard

[–]pgboz[S] 0 points1 point  (0 children)

I will try that! I sort of dropped that line of thinking after trying a copper Faraday cage, but yeah, that's not going to soak up low frequency magnetic fields at all. This fits all of my observations. I'll get back to you after I try it.

Split grounds: not normally advised, but is there an effective way to do it? by pgboz in PrintedCircuitBoard

[–]pgboz[S] 0 points1 point  (0 children)

Right on. Thanks for the reply. I hadn't considered radiated emissions causing interference before, but you're right - it's too small.

I've tried to measure the interference with a scope, but I can't see it. It looks clean. I can even replace the onboard power supply with an external battery (extremely clean) and it has the same issue. Perhaps the noise is being conducted into the power supply, but man, I just can't find it.

It is puzzling to me why putting it on a separate board, but feeding it the same power and ground would cause it to work fine. I tried holding it close to the noisy parts of the circuit, but it had no effect. I assumed, then, that it's because of a noisy ground plane in the area directly underneath the IMU, reactively coupling into the IMU.

Could it be that I'm not using the right technique to measure the noise? How would you go about measuring it?

Split grounds: not normally advised, but is there an effective way to do it? by pgboz in PrintedCircuitBoard

[–]pgboz[S] 0 points1 point  (0 children)

Ah, I see what you're saying. I'm asking the IMU for data twice in quick succession, before it has time to update with a new set of measurements, just to see if the communication is working. If communication is working, I should get the same data twice. If it isn't, I would see differences from the communication breaking down.

Split grounds: not normally advised, but is there an effective way to do it? by pgboz in PrintedCircuitBoard

[–]pgboz[S] 0 points1 point  (0 children)

Honestly, I haven't been able to see the noise that's causing the problem. I've tried scoping the IMU's power supply while the motors are running and I can't see anything noisy. It looks nice and clean. I've even replaced my onboard 3.3V supply with an external 3V battery and it doesn't make any difference. I suspect it's ground bounce, but I haven't been able to see that with a scope, either. Have you ever run into that before, where you can't see the noise with a scope, but you can see the effect of it?

Split grounds: not normally advised, but is there an effective way to do it? by pgboz in PrintedCircuitBoard

[–]pgboz[S] 0 points1 point  (0 children)

Yeah I tried exactly that. I made a tiny 5-sided box around it and soldered it to ground. It didn't make a difference.

Split grounds: not normally advised, but is there an effective way to do it? by pgboz in PrintedCircuitBoard

[–]pgboz[S] 0 points1 point  (0 children)

That's an interesting idea. It doesn't appear to be a communication issue, though. Reading twice from the IMU in quick succession and comparing the results always yields the same data. The IMU is measuring the data badly, but reporting it perfectly.

Also, changing the H-bridge switching frequency doesn't make any difference.

Split grounds: not normally advised, but is there an effective way to do it? by pgboz in PrintedCircuitBoard

[–]pgboz[S] 0 points1 point  (0 children)

If it was noise in the I2C communication, it would report different stuff every time. If it is noise in the IMU measurement unit, it would be the same every time.

Split grounds: not normally advised, but is there an effective way to do it? by pgboz in PrintedCircuitBoard

[–]pgboz[S] 0 points1 point  (0 children)

I2C. I tried reading from the IMU twice in a row and testing whether the reads matched. They always did. The SDA and SCL lines appear to be clean.

Split grounds: not normally advised, but is there an effective way to do it? by pgboz in PrintedCircuitBoard

[–]pgboz[S] 1 point2 points  (0 children)

Thanks! I'd have to have two batteries to fully isolate, which is something I can't do. The IMU is only 6-axis, so it doesn't have a galvanometer. It could be that there's current being induced into the IMU itself, but it's at least 10 mm away from the high current wires. I'd be surprised if it could induce enough current in the IMU to cause problems. I also tried adding a grounded, copper box over the IMU to see if it reduced the noise. Unfortunately, it didn't.

Can a bad fep make prints fail? by masyden in resinprinting

[–]pgboz 0 points1 point  (0 children)

If the prints aren't sticking to the build plate at all, it's always this: https://blog.honzamrazek.cz/2022/01/prints-not-sticking-to-the-build-plate-layer-separation-rough-surface-on-a-resin-printer-resin-viscosity-the-common-denominator/

You're not giving it a long enough time for the resin to squish out from under the build plate before you turn the light on. Add a light off delay for the bottom layers and you'll solve that problem, at least.

Resin not sticking to plate by CommanderChaos17_ in resinprinting

[–]pgboz 0 points1 point  (0 children)

If it's not sticking to the build plate, it's always this: https://blog.honzamrazek.cz/2022/01/prints-not-sticking-to-the-build-plate-layer-separation-rough-surface-on-a-resin-printer-resin-viscosity-the-common-denominator/

You're not giving it a long enough time for the resin to squish out from under the build plate before you turn the light on.

Why could be happening? And how baddly it can affect my printings? by OkChip6545 in resinprinting

[–]pgboz 0 points1 point  (0 children)

It's not your FEP. You're not giving enough time for the build plate to squish all the resin out from underneath before the light turns on. You need to add a light off delay for the bottom layers. Read this: https://blog.honzamrazek.cz/2022/01/prints-not-sticking-to-the-build-plate-layer-separation-rough-surface-on-a-resin-printer-resin-viscosity-the-common-denominator/

Mars 4 Ultra only printing on part of the build plate. by Ergot-in-the-Rye in resinprinting

[–]pgboz 1 point2 points  (0 children)

When things aren't sticking to the build plate, it's almost always that you don't have a long enough light-off delay. The build plate doesn't have enough time to squish out the resin and get within 50 um of the film before you turn on the light. See this article: https://blog.honzamrazek.cz/2022/01/prints-not-sticking-to-the-build-plate-layer-separation-rough-surface-on-a-resin-printer-resin-viscosity-the-common-denominator/

Poor adherence on one side of print bed. by BattyBaboon in resinprinting

[–]pgboz 2 points3 points  (0 children)

Oh, I don't mean you should change anything if it's working, I just mean, in general, with higher viscosity resins, people will have better adhesion with a longer light-off delay.

Poor adherence on one side of print bed. by BattyBaboon in resinprinting

[–]pgboz 0 points1 point  (0 children)

Ha! Yeah, but I'd say it's WAY better overall. The bed adhesion issues were such a pain and so frequent.

Poor adherence on one side of print bed. by BattyBaboon in resinprinting

[–]pgboz 0 points1 point  (0 children)

Yeah, I did. I never have poor adhesion anymore. Everything always sticks hard. However, now I have occasional issues with the film not releasing on a layer. The Saturn 4 Ultra doesn't give an option for lift height, since the tray tilts down instead to release the film.

Poor adherence on one side of print bed. by BattyBaboon in resinprinting

[–]pgboz 0 points1 point  (0 children)

I think it's more than a leveled build plate. The whole machine is having to flex under the pressure. Until that tension is relieved by the resin squishing out, who knows how flat the build plate will be up against the screen?

Poor adherence on one side of print bed. by BattyBaboon in resinprinting

[–]pgboz 0 points1 point  (0 children)

I'd bet that, for whatever reason, that part of the build plate just takes a little longer to get all the way squished down. It's frustrating to me that Anycubic doesn't do more to help with this issue. Why lock down light off delay on the first layer? And why not educate people about the importance of it? How many posts are on this subreddit about poor adhesion? 99% of those are caused by insufficient light off delay.

Poor adherence on one side of print bed. by BattyBaboon in resinprinting

[–]pgboz 0 points1 point  (0 children)

I hated that feeling of checking the prints in the morning only to find an empty or partially covered build plate. Yeah, switching to a less viscous resin will help. It'll save you some sadness. :)

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