isoprojkt, isolation "framework" project updates... - Page 1
Forum section: electronics / projects

author: eleguy
author_rank: Regular Contributor
timestamp: April 01, 2025, 12:31:17 pm
content: EDIT:: changed title to match current status of the projectIn many projects there is a phase when I have a programmer, an USB-serial converter and some other USB gadget connected to the device under development (DUT). Create/alter code, test, measure, quick hack PCB, repeat. Sometimes it just happens that I stick my tool in the "wrong" place (or just make a stupid stupid change). As a result (in the case of over current) USB host (my development computer) shuts down the corresponding USB port. Now it seems to depend a bit if the port comes back by unplugging and plugging the cable back or not. Pretty often stupidly reboot is needed. In addition to the lost uptime statistics (only linux guy might get this) it is pretty annoying to set up everything in place after boot. I would not either like to get my motherboard to be toasted if I managed to couple some high voltage pulse from the dc/dc converter for example. USB isolator to the rescue? Yes, it works but now there is yet another piece of something added to the small desk corner. Most of these converters seemed not to provide any power to the downstream (DUT and other gadgets). And the amount of needed cables between all these. So... I thought how hard it would be to pack this all into one device?The "isoprojkt" idea/features could be as follows* Use some USB isolator chip to get data isolated. Could be ISOUSB111 which is somewhat fast enough for programming/serial needs* Make some sort of smallish isolated DC/DC converter. Some low EMI push-pull-style maybe.* Take and limit total current to the available (USB-C / USB3). Resistor settable?* Separately limit DUT current (to 500mA?)* Utilize FT2232HL (witch works with the OpenOCD and is already proven by other projects) as a serial converter/programmer/gpio-provider** With this one can program/configure SWD, JTAG, i2c and SPI* Slam in RS-485 converter (as I need that often)* Utilize excess USB ports as isolated USB hub-ports for what-so-ever extra gadgets user wants to connect (or why not USB based DUT)* Add IO and PWR protection.It is easy to get excited from the own (simple) project idea so I thought to ask if anyone else would/could see any need for such? Also comments/deletions/additions to the "wishlist" will be appreciated. I know many features could be made with the MCU but this time I thought to survive without writing any code for the coding thingy...Thanks!

author: Nominal Animal
author_rank: Super Contributor
timestamp: April 01, 2025, 07:26:03 pm
content: I use isolators a lot, and had athread about using them in hobby projectsa year ago.I'm obviously only a hobbyist on the electronics side, but with lots of software development experience, so my solution path tends to the MCU side. For me, the main issue is the isolated DC power and its conducted and radiated noise.With USB 2.0 full speed (12 Mbit/s) isolators like ADuM3160 and ADuM4160 you can sustain about 1 Mbytes/s (8 Mbit/s) in one direction. These are very easy to use, and don't even require a crystal, but some USB 3 host ports may have timing issues, unless you have a hub between the port and the isolator. (The same applies to microcontrollers with native USB: if they do not have a crystal, some USB 3 host ports have issues, solved by adding a hub in between.)I would recommend using a USB 2.0 high speed (480 Mbit/s) isolator based onTI ISOUSB211orADuM3165/3166instead. The compatibility is much, much better with USB 3 hosts. I'd still use an isolated DC-DC supply, but with a DP3T toggle switch on the host side to select between host power, external wall wart power, and auto power via Schottky diodes; all go over the isolated DC-DC converter. This allows the isolated side to be referenced to any 0V potential one wants, safely. (Many USB wall warts reference the 0V output to the AC input via class Y safety capacitors, causing it to float 100-200 volts above the actual ground. I find it easier to just isolate their output than having to carefully test each USB wall wart before use. Even better is if you can use say a Mean Well Class II isolated supply to say 7V, and linearly regulate it down to low-noise 5.1V or so. I particularly like the idea of optionally selecting between 0V referenced to protective earth (ground pin on Schuko sockets), or to external device 0V.)Currently, I use aTeensy 4.0with an el-cheapo ADuM3160 isolator for similar purposes as you stated. Granted, my use cases are often overkill and deemed ridiculous by some other members here, but it does work well for me. I have several Teensy 4.0 at hand, and writing the firmware in Arduino/Teensyduino environment for each particular use case only takes minutes. (At USB high speed, it can trivially sustain 200+ Mbit/s or 25 Mbytes/s in one direction over plain USB serial using generic drivers in Linux; it's the tty layer (termios) that becomes the bottleneck. I've got the test program and Teensyduino sketch somewhere here and at PJRC.com forums; I use a Xorshift PRNG sequence initiated by the host to verify data stream correctness, so it is a real-world case with random data.)I have considered using aWCH CH32V307instead for this, with a 24MHz crystal providing the clock for both the isolator and the MCU, via JLCPCB Assembly (as they have both CH32V307's and ISOUSB211/ADuM3166's in stock for assembly). Adding a say 4-port USB 2.0 hub using one of the standard USB 2 hub ICs would be easy; the isolator definitely does not care at all, the only issue is the power supply to the hub.For UART (RX+TX, RX+CTS+TX+RTS) and SPI I do prefer using TI ISO6721/ISO7721, ISO6742/7742, ISO6741/7741, moving the isolation line to the UART or SPI bus instead, as these isolators work equally well as voltage level translators; they only need some milliamps of power at the preferred logic I/O voltage from the target device to run the other side of the isolator. They're also cheaper at LCSC/JLCPCB.ISO6721in particular supports 1.71V–5.5V (excluding 1.89V–2.25V) on either side, and a set of ten is under 10€ at LCSC and Mouser.I do have one incomplete design (currently using CH32X033, should shift to CH32V307) with three or four ISOx721 isolators that supports a combination of SPI and UART connections, separately isolated (so allows inserting it between an existing UART connection with isolation). I use EasyEda for such designs, putting all of them under Public Domain / CC0-1.0. TI ISOUSB does not require a crystal, but can get hot unless you use external voltage regulation; ADuM3166 requires a 24 MHz crystal or clock, but sharing the clock and the 3.3V/5V isolated side power with CH32V307 might be a simpler design.According to TIIsolated CAN FD Repeater Reference Design, ISO7721 seems to be a good choice for isolating the CAN bus transceiver too (although you obviously need to also support isolated 5V or so for the transceiver on the other side of the isolation barrier, using an isolated DC-DC converter). The idea in the MCU design is to connect many pins to the same isolator pins, so that you can enable or disable entire peripheral (tri-stating the relevant pins, so that only one is active per isolator pin at any given time), and thus select which peripherals are exposed over the isolators. This way the component count is very small. Also, as I use Linux, I can trivially use multiple USB Serial endpoints using the generic driver, specifically the first one for settings/control and status monitoring of the connections and data, with the rest reserved for the individual data buses. This avoids the need for any kind of host-side driver, a simple userspace application suffices.

author: thm_w
author_rank: Super Contributor
timestamp: April 01, 2025, 09:52:14 pm
content: Quote from: eleguy on April 01, 2025, 12:31:17 pmThey do supply power:https://www.aliexpress.com/item/1005001369085297.htmlYou can get 5V-5V DC DC modules for nothing:https://www.lcsc.com/product-detail/Isolated-Power-Modules_EVISUN-B0505S-2WR2_C7598622.htmlhttps://www.lcsc.com/products/Isolated-Power-Modules_13487.html

author: eleguy
author_rank: Regular Contributor
timestamp: April 02, 2025, 06:55:34 am
content: Many thanks for the detailed and creative thoughts!Quote from: Nominal Animal on April 01, 2025, 07:26:03 pmLow EMI design is not a bad idea. More care in routing, stackup, converter/component selection and filtering. Converter could be also lightly shielded with some general RF shield. Hmm... isolation and shielding don't fit together so well....Quote from: Nominal Animal on April 01, 2025, 07:26:03 pmI think ISOUSB211 was one option that popped up but maybe I got scared by the price. Nevertheless this is very good point to consider.Quote from: Nominal Animal on April 01, 2025, 07:26:03 pmThis is a good point and not too hard to implement. And why not "auto" mode as well.Quote from: Nominal Animal on April 01, 2025, 07:26:03 pmAaa, do you mean that one could power the "secondary" (=isolated) side with this isolated supply and not utilize the "on-board" converter at all? This is interesting idea! The USB isolator would be still powered by the host, right?You have clearly though these matters deeper. I need to think littlebit. So, the power could come from a) USB host, b) wall wart power (5V) supply, c) super duper quality (higher voltage) wall wart (or bench supply) inserted to the secondary side.I have thought that the thingy would create normally used rails for DUT (1V8, 3V3, 5V) [would 2V5 be needed or should this be made fully variable?]. User could select between these or make the DUT "self powered".Quote from: Nominal Animal on April 01, 2025, 07:26:03 pmSo I thought as well.Quote from: Nominal Animal on April 01, 2025, 07:26:03 pmI am familiar with the I2C isolator ISO1643 but have not isolated SPI earlier. The list of isolators bumps up quickly. That is why I though to isolate an USB hub and have FT2232HL connected to it. Now everyhing this chip supports would be isolated. Level conversion is something that has to be implemented as well. I just was not yet so deep inside this matter. Thank you for reminding! Maybe some "basic" translators like SN74LVC2T45 but just with more pins could do the trick.Quote from: Nominal Animal on April 01, 2025, 07:26:03 pmI have not yet deeply read (specially not understood) the manual but quickly it seems that ISOUSB211 1V8 creation is the heat source. It can take almost 100mA in worst case. Seen as ~0.3W regulator heat dissipationper side. Maybe they use heat waves in isolation?Quote from: Nominal Animal on April 01, 2025, 07:26:03 pmThere seems to be similar type push-pull converter I thought to use in this. Maybe SN6505B (instead of SN6501) to get enough power to the downstream.Quote from: Nominal Animal on April 01, 2025, 07:26:03 pmI am mostly familiar with nRF52 and ESP32 MCUs. I am not any super duper coder but can do "some" stuff with the Zephyr that has shell option build in. I thought first to make (most) MCU based in the way that one could change the mode, DUT voltage, ... using his/hers console (via shell). Creating something that supported programming/debugging also started to feel bit a work so idea got diverted to this direction.Quote from: Nominal Animal on April 01, 2025, 07:26:03 pmOnly Linux is used here as well. Gadget has to work with the normal kernel drivers and OpenOCD without any hazzle. Certainly I would try not to prevent it working in other operating systems as well. eh eh...Again many many thanks for your thoughts and shared experience!Next I will scratch up some high level diagram and share it here. Let's see if this makes any sense after visualizing the idea a bit.

author: eleguy
author_rank: Regular Contributor
timestamp: April 02, 2025, 07:00:43 am
content: Quote from: thm_w on April 01, 2025, 09:52:14 pmAh, yes. Forgot to mention those little (royer oscillator based?) converters. They are often rated only 1W and are very noisy. But good point. These are handy "black boxes" but not enough to fulfill initial "specs".

author: eleguy
author_rank: Regular Contributor
timestamp: April 02, 2025, 11:31:46 am
content: First idea->"picture"

author: Nominal Animal
author_rank: Super Contributor
timestamp: April 02, 2025, 09:37:11 pm
content: I do recommend you take a look atMean Well GSM18E07-P1JGSM18E07-P1J, andGST18B07-P1Jmedical rated low leakage class II isolated 7.5V 2.0A AC/DC adapters with a standard 5.5mm/2.1mm 11mm long center-positive DC barrel jack output.The B models have anIEC 60320 C8AC connector (the common figure-8 two-pin one). They all havehigher power models, too, if you want more current capability.I've had my eye onGSM36E07-P1JthatReichelt sells for 21€; 7.5V at max. 4.32A, medical-rated class II isolated wall wart, EN 55011 class B like the others above. The idea being I'd use this to power the isolated side using a standard Ø5.5mm/2.1mm 11mm DC jack, with each 5V/3.3V output using their own linear regulator. Ibelievethat if I filter the AC/DC output using a Pi (CLC) filter, I can keep out any conducted noise from the wall wart.Still, I'd like even more to use a Hammond cast-aluminium enclosure (that you can get very affordably from Uraltone in Helsinki), itself grounded to protective earth on the Schuko wall socket, with the AC/DC converter, power switch, and the CLC filter inside, with innards protected using polycarbonate sheets etc.Mean Well RPS-65-7.5would be optimal for my needs, but as I'm not a company, it's difficult for me to buy these from standard sources. Plus, 240VAC is scary. Me zap myself no like.Quote from: eleguy on April 02, 2025, 06:55:34 amMy intention has been to create my own ISOUSB211 (C5772877, 9.31€) or ADuM3166 (C7453661, 10.05€) PCB assembled at JLCPCB from the get go.With the abovementioned Mean Well supplies, I'd power the host side from the host, but the isolated side from the Mean Well supply, linearly regulating from the CLC-filtered 6.5V–8V to 5.0V–5.2V (adjustable would be optimal) per USB port, and a separate regulators to 5V→3.3V→1.8V powering the isolator isolated side. Again, the entire thing would be in a cast-aluminium enclosure, with the enclosure itself grounded to protective earth.Yes, this would mean that I'd have two aluminium enclosures on my desk, but as long as they stack nicely with rubber feet, I'm okay with that.The isolator PCB design is not at all scary, actually, because there are lots of good examples out there. For ADuM3160, take a look atStefan Wagner's USB isolatorproject; it's very straightforward, especially if you remove the DC-DC converter and the EMI/EMC noise issues it causes. For ISOUSB211, thedatasheetand theevaluation module notes (SBOU261)show that it's simple compared to say designing a switchmode converter circuit.Quote from: eleguy on April 02, 2025, 06:55:34 amI mostly need 5V, although it would be nice to fine-tune it between 5.0V and 5.25V, say at the linear regulator stage. I particularly like the idea of using an additional P-MOSFET for MCU current control (noting that most hub ICs have that internally, some allow control via I²C), then a shunt resistor for current measurement, and then an adjustable linear regulator per USB output. One thing I want to avoid is power-on overshoot.For the other rails, I rarely need them. I do have a Gophert NPS-1601 supply (cheap, but no overshoot when enabling output) for those use cases. Perhaps have an extra output, CLC-filtered from the AC-DC supply but not regulated further (so is assumed to be between say 6.5V and 8V), that one could later use for "add-on" modules to regulate down to lower voltages? Using a three-pin connector (+VDC, 0V, protective earth)?(I don't like "frameworks", and much prefer modular approaches to problem solving. That lets me start with a small and simple core solution, and build on top as my needs evolve. Those who want everything in a single small compact unit won't like my implementations!)Quote from: eleguy on April 02, 2025, 06:55:34 amFor fixed-direction buses like UARTs and SPI, I like to use TI TXU0n0mtranslators, specifically TXU0102, TXU0204, and TXU0304, and keep 74LVC1T45 in SOT23 at hand for hand-soldering (even dead-bugging directly to wires, just heat-shrinking over the top). For wider buses, 74LVC8T245.Bidirectional voltage level translators tend to have a "step" in the low state whenever they confuse the data direction. In many cases this is ignored (because the low state stays within the translator specs), but some of my MCUs and SBCs have so low input thresholds (or perhaps the wiring has too much inductance?) that this "step" can occasionally be confused as a transient high, causing comms errors. This is why I avoid those for unidirectional use cases, and only use them for I²C.Quote from: eleguy on April 02, 2025, 06:55:34 amExactly. It would be nice to use some kind of a buck converter for these (but EMI/EMC?), or at least have nice heatsinking for the LDOs. I'm not comfortable using the internal LDOs due to this heating up effect.Also note that the TI ISOUSB211 uses capacitive coupling, whereas ADuM3166 uses iCoupler magnetic coupling. As I use isolators with max. 450VAC potential difference (worst case with wall wart supplies, when one uses grounded supply with 0V close to true ground as in desktop computers, and another ties it to the live, as in a cheap wall wart that assumes one prong is "live" and the other "neutral" and our sockets not being polarized that way gets the opposite), and I've understood that the capacitive coupling is less EMI-noisy (but limited wrt. isolation capabilities), I do believe ISOUSB211 is better suited for our kinds of use cases here in Finland.Quote from: eleguy on April 02, 2025, 06:55:34 amFT2232 sounds like a good match for that. Note that it too can use high-speed USB (480 Mbits/s), or you can limit it to full-speed USB (12 Mbit/s) in which case ADuM3160 suffices.If you do use ADuM3160, do note that then all the USB hub ports would be limited to full speed, withcombinedthroughput that 12 Mbit/s. I would not want to use a hub like that. But, if the only thing you connect to it is the FT2232, or if you use the hub to easily allow using the FT2232 or the isolated full-speed USB port (so even a basic 2-port hub IC like USB2422 would suffice), not both simultaneously, I think that'd be okay.

author: eleguy
author_rank: Regular Contributor
timestamp: April 03, 2025, 10:49:50 am
content: Quote from: Nominal Animal on April 02, 2025, 09:37:11 pmThanks for the hint. These seem to be reasonable priced.Quote from: Nominal Animal on April 02, 2025, 09:37:11 pmWhy should the USB voltage be adjustable between 5V-->5.2V? Separate regulator per level is something I originally thought but if "too many" voltage levels need to be supported then variable version would make more sense. Then thoughts about the protective earth which would be only seen/connected through usb cable that is connected to host. I have to sometimes attach debugger/configurator in "live" meaning DUT is AC powered having it's DC rails generated from that. I might not like to push in metallic casing into such "cabinet". So, here we have two separate use cases. But certainly the design size/form could be made so that it would fit in some off the self box as well. I have some times used such boxes and noticed that it is not so straight forward to make nice and precise rectangular holes into those by hand. Drilling holes is fine.Quote from: Nominal Animal on April 02, 2025, 09:37:11 pmNo, I am not scared at all. Is it so due the lack of knowledge or gathered experience? Don't known...Quote from: Nominal Animal on April 02, 2025, 09:37:11 pmI have thought the same and then hesitated if the shunt should be part of this idea or not. Well, if the system uses such internally why not to expose buffered "result" in the way or other.Quote from: Nominal Animal on April 02, 2025, 09:37:11 pmI am yes, no and between guy. Depending on the case. However, typically end users have been most happy with very simple things. Those cases where everyone's favourite feature has been implemented have turned out to be endless projects where no-one is happy about the expensive outcome.Quote from: Nominal Animal on April 02, 2025, 09:37:11 pmI have not used those and was not aware about this "feature".Quote from: Nominal Animal on April 02, 2025, 09:37:11 pmI have used ISOUSB111 in my designs but maybe it could be a time to move forward.Something where I always end up debating with my self is whether to use 2-port or 4-port HUB chip when utilizing one at the first place. I am not sure how often people really need "many" isolated ports. Maybe just one (exposed) is enough (as one would be eaten internally by FT2232)?Thank you again for your time in responding and thinking this matter. I might need to crawl back into my cave and think into which (if any) direction one should continue from here.

author: Nominal Animal
author_rank: Super Contributor
timestamp: April 03, 2025, 07:35:34 pm
content: Quote from: eleguy on April 03, 2025, 10:49:50 amFor testing. Technically, USB supply voltage can vary between 4.5V and 5.5V. Some devices like MCUs tend to work well across the entire range, others like display and sensor modules can be much pickier. For my display projects, I like to adjusting the supply slightly to verify the backlight isn't affected too much.Quote from: eleguy on April 03, 2025, 10:49:50 amYep. For precise holes, you need good (expensive set of) metal files and time and patience.One important design decision is exactly where the isolation device is: near your host computer, or near the FT2232/MCU/device. External power needs to be injected at the isolation device, unless you also have a (EMC/EMI-noisy!) isolated DC-DC converter there.My exact needs differ from yours, because all my targets are small and fit easily on my workbench. Currently, I use┌────┐ ┌───┐│Host╞══USB══╡MCU├ISO── Target└────┘ └───┘with TI ISO6721 isolators, with the target providing the few milliamps to power the isolator target side, at its preferred logic level voltage; and┌────┐ ┌───┐ ┌───┐│Host╞══USB══╡ISO╞══USB══╡MCU├─ Target└────┘ └───┘ └───┘with cheap ADuM3160-based isolators. The current budget at the MCU is typically 200mA, and while the isolated DC-DC converters work fine for digital stuff, I wouldn't want to try to do any ADC stuff due to the supply ripple and noise.The simplest thing that would work for me would be a TI ISOUSB211 isolator with a 5.5/2.1mm DC barrel jack for powering the isolated side via 6.5V – 8V DC, linearly regulated down to 5V or so. (Having that adjustable between 4.5V and 5.5V would be useful, too.) Having a hub and an MCU on the isolated side to monitor the per-port current draw –– presence of fast spikes, and average current draw –– would make it particularly useful to me. Say,┌────┐ ┌───┬───┐│Host╞══USB══╡ISO┆HUB╞══USB══└────┘ └───┤MCU╞══USB══AC──────┤+DC╞══USB══└───┘Now, consider the case where the AC/DC conversion is with the Mean Well RPS-65-7.5, with a grounded Schuko plug, providing three high-current connections to the isolated side: 0V, 6.5V-8V (CLC filtered but not regulated), and true ground, with the other twonotreferenced to true ground by default, but can be (because of isolation and low leakage at the AC/DC conversion, so careful choice of AC/DC converter!).(Or, equivalently, one of the Mean Well wall warts I listed, and a separate wire or connection to true/protective ground.)Then, at the isolated/target side hub, we have well-filtered linearly regulated 5V that we can reference to any 0V reference,orto true ground, whatever we prefer. We can also linearly regulate other (5V or lower) rails because of the high current capability. Having the true ground for e.g. wrist straps is also nice, since my bench is an ordinary wooden table, not an industrial workstation with bells and whistles like grounding points.(A banana jack for true ground, for grounding the chassis or 0V rail of the target device, would be nice too. That way, one could check using a DMM in current mode if there will be significant ground current when only the ground wire is connected. And when used, the ground wire would be connected first to the target before the target is powered, say with a banana-alligator clip, to ensure no spikes due to equalizing reference potential when turning it on with data stuff connected.)For ADC stuff, if the isolated side provides additional separately regulated 5V and 3.3V, free of digital noise, I can quickly cobble together all kinds of ad-hoc measurement tools on the isolated side based on my existing MCU development boards and I/O modules.That alone will not solve all my needs. As I mentioned earlier, I have a design I intend to use WCH's CH32V307 for, specifically┌───┐┌────┐ │ ╞═ISO6721══ I+O│Host╞══USB══╡MCU╞═ISO6721══ I+O└────┘ │ ╞═ISO6721══ I+O│ ╞═ISO6721══ I+O└───┘(or two ISO6742's) where the four separately isolated input-output pairs can be used as 2 separate UARTs with hardware flow control, a SPI master, a SPI slave, or some combination, depending on the exact MCU used and its pin multiplexing. (WCH's MCUs tend to select pin function for an entire peripheral at a time, rather than per-pin which is more common on ARM MCUs.) This is the interfacing module you use FT2232 for.The issue here is that the I+O sides of the isolators also need a few milliamps of current to drive that side of the isolator, at the preferred logic level voltage (which can be 1.8V or 2.25V–5.5V with ISO6721 and ISO6742). Thus far, all my target devices do that, even Odroid HC1 with its 1.8V serial console UART. If I find I need the external power, I think making it possible to insert a small isolated dual adjustable 1.8V-5.5V supply between the target and the I+O signals, providing the power for the target and the isolator target sides.Note: I'm only pointing out what I've found useful thus far, and how I think I will evolve my tools from here onwards. I only show it here in the hopes that it might be helpful to someone having similar needs; the posts on this forum are easily discovered via web searches too.Quote from: eleguy on April 03, 2025, 10:49:50 amNo, I meant scaryfor me, me being just a hobbyist on the electronics side. I only "do" low voltages and through-hole and SMD packages with legs, avoiding BGA (and QFN).Quote from: eleguy on April 03, 2025, 10:49:50 amI think a 2-port one is enough. The hub I use most often with my projects is one of those cable types, with one USB-A male on the upstream side, and a female, a mini-B, and a micro-A on the downstream side. I don't think I've ever used more than one downstream port on it at any given time.After all, one can always use a passive USB hub after the isolator, if additional ports are needed.It's more the +5V supply than the USB data that I find often useful, having the same 0V reference, but none of the digital noise (if separately regulated, of course). I could equally well use some other connectors, I guess.

author: BennoG
author_rank: Frequent Contributor
timestamp: April 03, 2025, 07:59:32 pm
content: why not simply use usb isolator without DC/DC converter but a bench power supply for the remote 4.5 - 5.5V (or anything else you like).Then you don't have the noise from the DC/DC and the low noise from a quality bench PSU.Benno

author: Nominal Animal
author_rank: Super Contributor
timestamp: April 04, 2025, 06:26:24 am
content: For the same reason I don't have any of the existing ISOUSB211 or ADuM3166-based USB 2.0 high speed isolators, either: the good ones are way too expensive, and either the cheap ones do not exist (high-speed isolators) or are suspect (power supplies).Many lab supplies also suffer from a voltage spike when turned on/output enabled. The cheap Gophert NPS-1601 that I have do not suffer from that, but it wasn't easy to find that out.Considering how cheap the Mean Well medical supplies are, and how easy it is to CLC filter and linearly regulate the output to 1.8V–5.5V given sufficient heatsinking, to me the solution is obvious: make the tool to fit the needs, since the existing ones cost over 10× as much, and even then may be inferior for these particular use cases.I'm sure many disagree. They also told me my uses of isolators was ridiculous, since "the obviously correct" solution was to power everything from lab supplies and not bother with isolation. Because many of the devices I work withhave todeal with el-cheapo wall wart supplies or built-in supplies, such solutions just aren'trealisticfor my use case. If you don't understand that, then you simply haven't the same kind of use cases I do, or don't care about the differences between device investigation and interfacing in the real world, and in a perfect lab environment.

author: eleguy
author_rank: Regular Contributor
timestamp: April 04, 2025, 07:40:34 am
content: Quote from: BennoG on April 03, 2025, 07:59:32 pmOne of the points in the original idea was to get rid of "too many boxes" in the first place. I often have to work on site - meaning less stuff to carry better.

author: eleguy
author_rank: Regular Contributor
timestamp: April 04, 2025, 08:34:10 am
content: Quote from: Nominal Animal on April 03, 2025, 07:35:34 pmGood point. I have somehow managed to yield this mostly because a) utilize system in lower voltage than 4V5 b) create own rails with a dc/dc converter (that support levels down to 4V5 or less).Quote from: Nominal Animal on April 03, 2025, 07:35:34 pmThis fits well into my thoughts as well.Quote from: Nominal Animal on April 03, 2025, 07:35:34 pmHmm, how much current you typically need? Regulating this down to say 1V8 -> little heater. If only to 5V then tolerable.Quote from: Nominal Animal on April 03, 2025, 07:35:34 pmI have "dissipative vinyl mat" connected to ground-ground through resistor. It came with the wristband and connector but I have only tested it once. Seems to work but don't really use it. Maybe if I ever have ESD sensitive $1000 part in the bag waiting I think again.Quote from: Nominal Animal on April 03, 2025, 07:35:34 pmNot a bad idea.Quote from: Nominal Animal on April 03, 2025, 07:35:34 pmIt should yes, in the way or other. Certainly "noise free" is something that has to be defined. Hopefully target level is not "lead battery" (stupid joke).Quote from: Nominal Animal on April 03, 2025, 07:35:34 pmIs it price, "challenge" or something else why this is interesting? I was earlier really really trying to push BOM price down. Then noticed that pretty often by selecting the cheapest "not known part in the west" the total cost was actually bigger thanks to harder sw development. Now I tend still to optimize BOM a lot but with MCUs I have settled to (Zephyr supported) nRF52 and ESP32. In the idea what we are talking here (for example) there is no difference if the MCU costs 10c or $1+. With more memory one can also do many interesting things. ESPs have plenty.Anyhow, MCU based (non FT2232) direction is also interesting but maybe would not like to end up remaking thishttps://black-magic.org/index.htmlQuote from: Nominal Animal on April 03, 2025, 07:35:34 pmAvailability, easiness and cost are certainly things to consider. From this came to my mind that nRF has "cool"(?) aQFN (a=advanced) as one footprint. It took couple try-outs before fabhouse was ready to manufacture first such board in their normal budget friendly process.Thank you again for your time and thoughts!

author: eleguy
author_rank: Regular Contributor
timestamp: April 04, 2025, 11:26:30 am
content: Second idea->picture drawn during the coffee break attachedMCU would bring nice "shell option" to set the voltage, access the protected io and read/record current. It also complicates stuff a little and is partially duplicate with the stuff FT2232HL can do. Hmm.... have to still crawl the net and think a bit.

author: TJ232
author_rank: Frequent Contributor
timestamp: April 04, 2025, 02:31:23 pm
content: Used this kind of isolated programmer for many years:https://esp8266-projects.org/2018/01/usbprog-v8-6d-new-device-release/I have around also an updated version with UPDI interface option for the newer MCU class like latest Attiny if interesting can post about.

author: Nominal Animal
author_rank: Super Contributor
timestamp: April 04, 2025, 11:16:38 pm
content: Quote from: eleguy on April 04, 2025, 08:34:10 amSome of my SBCs can be powered from USB 5V, drawing several amps. The worst "offender" is my old Odroid HC1 with a SATA connector (no 12V support!).Mean WellRPS-30-7.5is the lowest-current of this series, providing 7.12V–8.3V @ 4A;RPS-45-7.55.4A, RPS-60 is class I, andRPS-65-7.5provides 8A. The three have the same size PCB, too: 76.2mm × 50.8mm, with four Ø3.2mm holes at 69.85mm × 44.45mm center-to-center rectangle. If you look at the prices at e.g. TME, RPS-30-7.5 costs 14.93€ (incl. VAT), and RPS-65-7.5 costs 18.57€ (incl. VAT).While the four variants are interchangeable in the design (PCB, voltage adjustment range, PCB size, mounting), only with differing maximum current, I suspect RPS-65-7.5 is the best bang for buck for me, that's all.I really like Mean Well IRM and MPM series encapsulated AC/DC modules, but they don't have any 7V or so models; only 5V and 12V.For the wall warts, lower-current ones are much cheaper than the higher-current ones. At Reichelt,GSM36E07-P1J(4.32A) andGST40A07-P1J(5.34A) costs half that ofGSM60E07-P1J(6A), withGSM60A07-P1J(6A) in between.For 3.3V and 1.8V rails, one could consider e.g. a separateIRM-05-5AC/DC module (5V 1A class II, 45.7mm×25.4mm×(21.5mm+3.5mm pins) encapsulated module) filtered and linearly regulated down. The module has up to 200mVpp noise, and is not medical rated, with maximum 0.25mA leakage at 277VAC, but Reichelt sells them for8.43€incl. VAT.For my desktop cast-aluminium box, I think the box itself would act nicely like a heatsink.Quote from: eleguy on April 04, 2025, 08:34:10 amI cannot even quantify the noise level I need properly... I simply think in terms of "capacitor, inductor, capacitor, linear regulator, capacitor", picking the linear regulator first, then the capacitors based on its and the AC/DC converter datasheet, and finally pick an inductor with sufficient current limit and low enough DC resistance to not get too hot but also not costing more than a couple of euros, and live with what I get.With multiple outputs, the filter is shared, but each one has their own linear regulator.Quote from: eleguy on April 04, 2025, 08:34:10 amI like to use open source toolchains, and not rely too heavily on vendor SDKs and HALs; seegithub.com/openwch/. I have lots of time, but very little money. I like RISC-V design, and consider the Chinese RISC-V implementations superior to their ARM cores. I specifically want USB 2.0 HS (480 Mbit/s), and a non-BGA/QFN package. I don't like the idea of a radio in a wired-USB MCU. Combining these wants, CH32V305FBP6, CH32V305RBT6, CH32V307RCT6, CH32V307VCT6 are very enticing. In particular, CH32V305RBT6 in LQFP-64M (C5187529) is just 1.81€ in singles at JLCPCB assembly, has 32k of SRAM, 128k of Flash, USB 2.0 HS PHY (and another FS PHY), useful peripherals (5 USARTs, 2 I²C, 3 SPI, 2 CAN, 2 ADC, although only a subset of these can be used at the same time), running at up to 144 MHz at 3.3V.The main reason for me for having an MCU on the isolated side with a hub is to measure the per-port current, and perhaps show these using either small 7-segment displays or <1" OLED display modules (as well as providing an USB serial access to the data), or perhaps BuyDisplay0.96" ER-TFT096-1 80×160 IPS TFTmodules using SPI and 18mA (3.1V–3.3V) backlight. Something likeINA219,INA220orINA226per USB port would be nice. I imagine also having a toggle switch (to enable/disable port power) and a pot to adjust the voltage (some sub-range between 4.5V and 5.5V, preferably by controlling the voltage divider in a linear voltage regulator). If using a graphical display – noting that the IPS TFT and OLED modules only need to be written when the display contents need to change; their internal controller will maintain the same image ––, it would show the voltage, whether VBUS is enabled or not, the average current, and the peak current within the last second or so. Those OLEDs definitely need their own linear regulator, as their current draw is very spiky/digital; the 18mA backlight can be powered from 5V using a ~ 133Ω resistor for example, only wasting 40mW as heat in the resistor.Quote from: eleguy on April 04, 2025, 08:34:10 amQuite.For that reason, the 5.5/2.1mm DC jack for supplying isolated side power linearly regulated to ~ 5V, would be the optimum place to start. Even if one uses it mainly for experimentation/test design, it will remain useful as is even if one creates derivatives by adding an USB hub, MCU, et cetera. It isn't what the thread title says, but nevertheless an useful stepping stone on the path of getting there –– unless one wants to do a final design from the get go. I don't want to do a final design from the get go, because as a hobbyist, I'm sure I learn much from doing the stepping stone and examining my use cases with it; and therefore my final design is likely to change on the way there.

author: voltsandjolts
author_rank: Unknown
timestamp: April 05, 2025, 08:50:13 am
content: If including a psu for the DUT, some readback of voltage/current would be very useful, perhaps with reasonably fast current sampling, like 1kHz say. Plotted on host screen. So you can see DUT mode changes or firmware whoopsies. Then maybe some general purpose digital IO, could also be plotted, like mini logic analyser, time correlated with volt/current plot, so you can see where firmware caused power draw changes. Like Beagle USB, orNordic PPK. Or maybe asimple sigrok analyserbuilt-in. Or maybe...er, maybe I should calm down!

author: Nominal Animal
author_rank: Super Contributor
timestamp: April 05, 2025, 09:07:35 pm
content: Quote from: voltsandjolts on April 05, 2025, 08:50:13 amI feel you; checking for spiky current draw (and report it via USB HS serial) is the main reason I want a MCU in the isolated supply side. Displaying the voltage and current et cetera would just be icing on the cake; I have plenty of experience with that (usingBuyDisplay/EastRising IPS panels, directly from them via web, eBay, or Aliexpress), so that part is easy-peasy for me. (The backlight is the only thing that gives me pause, because Ihateflicker; for the smallest/single white LED ones, resistor limiting is perfectly okay, and I can use NX138AK for low-side PWM if needed –– it's a N-MOSFET similar to BSS138, but faster due to smaller total gate charge.)The way I solve that feeling/impulses/desires, is via modularity. I like to overprovision the MCU used, with stuff like the filtered but unregulated power available on pins, unused I/O pins exposed on a header, so I can later add "modules" to do what Iactually need. I also like to keep the design (including schematic) modular, so I can create derivative designs incorporating later ideas.For Sigrok stuff, I already have one fx2lavf (24Msamples/s) -based one, so if I hadtwoof these isolators –– okay, needing two wall warts might be a bit annoying, but that's why I use a power strip tied to the side/underside of my workbench –– I'd be ready to go.This is exactly why I think a USB HS isolator project without DC/DC conversion, just a 5.5/2.1mm DC input jack (say, for 6.5V–9.5V) CLC-filtered and then regulated down to downstream 5V (and the other voltages the isolator needs), in a solid cast aluminium box with grounding carefully thought out (including using host chassis ground for the enclosure but not for the USB reference, sounds such a good first step for me. I can easily do the schematics and even PCB layout in EasyEDA or KiCAD, but it is the chassis grounding scheme in such an isolator that I'm less sure of. With plastic enclosures it is much easier, but also makes it easy for the cabling to become an antenna.The case that worries me is when the downstream 0V reference varies with respect to host chassis ground: this happens with class I isolated wall warts that happen to tie the 0V reference to the mains live via a class Y safety capacitor (because we do not have live/neutral -polarized mains here), and the target device is otherwise (double) insulated. It is a common occurrence here with USB wall warts and similar appliance supplies. Direct connection would obviously defeat the purpose of the isolation here. Any kind of capacitor/resistor-based tying of the two shields/grounds will lead to leakage/ground currents, and I'd like to avoid those.I need the help from an experienced EE for this, or I'd have done this years ago! And asthis thread I startedshows, I'm still learning how to do grounding and shielding properly. My hobbyistness shows

author: eleguy
author_rank: Regular Contributor
timestamp: April 06, 2025, 06:18:48 am
content: Quote from: TJ232 on April 04, 2025, 02:31:23 pmI used somewhat similar arrangement before but now when ESPs can mostly be programmed over USB those days are gone (when developing something new). Then again when accessing "random" target I would like to have as much "adapters" in my back as possible. Therefore I thought to utilize FT chip. I have not worked too much with the Microchip stuff.

author: eleguy
author_rank: Regular Contributor
timestamp: April 06, 2025, 06:22:03 am
content: Quote from: voltsandjolts on April 05, 2025, 08:50:13 amHahahaa!! Yes, Zillion-in-one!But in reality MCU based voltage control (for example) can turn out to be even cheaper than "fancy" knob solution.

author: eleguy
author_rank: Regular Contributor
timestamp: April 07, 2025, 12:54:30 pm
content: Third idea->picture attached where isolation layer is moved bit "forward". Maybe there is no need to re-invent the protection as those sturdy isolators have quite a lot as-is. Then I decided not to make an isolated USB HUB (that was not even in the original idea). Instead focus on the development and there one USB (for DUT) is enough. One can always push in external USB HUB if needed. However, on the host side 2 port one is needed in order to get MCU USB to function separate from the DUT USB. I am now somewhat confident than with "some head to wall algorithm" it is possible to live without FT chip. DC/DC conversion is still as it was. However, if one pushes in external power to the isolated side then the DC/DC would be turned off. Voltage can be set over i2c as well the current/voltage can be monitored in the same way. Starts slowly to look like something? Open areas (at least)1) To have or not to have a display (thanks to Nominal Animal)2) Should there be (extra) internal/external extension connector? Could be used for ADC/DAC or what so ever. Or is the IDC (or similar) connector enough/good for such as well?3) How many GPIOs should there be? Now there is i2c + 8 IN + 8 OUT. Or then i2c + 8 bidirectional (and live with the glitches). Or something else?

author: eleguy
author_rank: Regular Contributor
timestamp: April 09, 2025, 08:31:41 am
content: After some digging I think I am ready to list some pre-selected parts.Host/border "side"====* TUSB4020, high-speed two-port port USB2 Hub [4.15/2.35]* ISOUSB211, high-speed USB isolator [12.02/7.41]* ISO164x, I2C isolator (ISO1644 in price) [4.63/2.64]* ISO67x0, digital isolator (ISO6721 in price) [1.3/0.66]* SN6505B, 1A (low EMI) transformer driver [2.1/1.12]Isolated "side"====* TPS7A47, 1A low-noise "any-out" LDO. (not yet sure about this) [4.58/2.61]* TCA9538, I2C IO extender [1.44/0.74]* INA236, I2C 16-bit power monitor [1.99/1.06]Almost sounds like I am an TI fanboy. Well they make proper stuff...Few words about the cost of this all. Added prices after corresponding parts [1 piece/1000]. Prices are from digikey (in EUR). So far total [32.21/18.59]. In addition what is listed above one needs a transformer, mcu, board, display?, connectors and common parts from y to z.

author: voltsandjolts
author_rank: Unknown
timestamp: April 09, 2025, 06:21:32 pm
content: Regarding external power supply, could you provide standard 0.1" header pins for the power input. These would work perfectly with theNordic PPK2power profiler. Although, that is USB powered and non-isolated.May I also suggest two header pins for each digital I/O signal - one to connect to DUT and the other for monitoring on scope or logic analyser.

author: eleguy
author_rank: Regular Contributor
timestamp: April 10, 2025, 05:41:52 am
content: Quote from: voltsandjolts on April 09, 2025, 06:21:32 pmI have thought to have an IDC connector for DUT which is based on "standard 0.1" header" just that is has that plastic connector socket around. One can stick there cables without connector as well. For DUT measurements I would put PPK2 between power pins offered by IDC and DUT. Having PPK2 between external power supply and "isoprojkt" (connector type(s) not yet decided) one ends up to measure internal currents consumed by isolation converters, ldo, etc. Or maybe I just did not get your use case?Quote from: voltsandjolts on April 09, 2025, 06:21:32 pmMy thoughts almost got diverted from this. It is after all a good idea (specially if isolated VUSB_DUT was adjustable for testing purposes) to separate VUSB_DUT and isolated VDUT. In this case one can stick PPK2 (for example) to the isolated USB port and use it to measure current consumption of the VDUT "as-is". Thank you for reminding!However this makes me to think if the VUSB adjustability is needed or not as such test could be done without as well. Hmm... more thoughts -> more thinking...Quote from: voltsandjolts on April 09, 2025, 06:21:32 pmThis is a good idea. I can easily imagine how I would also utilize such "feature" on DUT power pins as well. However, now it has to be thought if some buffering is needed to avoid the noise, potential reflections and what so ever. Let's see...EDITJust came to my mind if connecting the logic analyzer is the "main" thing then placing such an extra io-connector to the host (non-isolated) side would enable isolated access (to DUT thought isolators) to your logic analyzer. There it would be pretty straight forward to buffer signals. For an o-scope situation is bit different. Why would such be needed for every io? For checking the signal integrity yes, but hmm... maybe I am just thinking too much stuff from the protection / noise point of view. Plugging in grounded scope to the isolated side makes stuff less isolated and can ruin your day.

author: eleguy
author_rank: Regular Contributor
timestamp: April 10, 2025, 02:59:44 pm
content: Fourth idea->picture attachedThings got just simpler. Why not to make the project to be as the title says "isoprojkt"? Mostly about the isolation/low noise and less all-in-one. So, one can utilize isolated side connectors for the DUT as before. I have also added a connector to the "host" side. Calling it (name under development) as "an access connector" as from there you can access the isolated side in isolated manner. Thought to have an IDC connector here as well. From here you can use only few pins to get UART isolated (for example) or make own board that uses all possible isolators. I also decided to add a simple-sample access board to my planning list. So, something that has (some arduino+Zephyr supported) MCU mounted and provides shell/uart/VDUT selection/current-monitoring to the USB host (terminal some likely). This way one can start to utilize most features without designing "anything" him/herself.Stuff looks now much more thought. Next I will re-iterate main parts and see which are (after latest idea changes) best fitting. Maybe still one high level idea picture and then to the schematics level. I hope...

author: eleguy
author_rank: Regular Contributor
timestamp: April 11, 2025, 10:31:53 am
content: Schematics work has scratched the surface.Conceptually I like to work from "in to out" meaning first things (=those things I think) first. Thingy won't work at all without power and data. Power first. I am going to push somewhat lot capacitance on the Isoprojkt board. At least if comparing to USB2 10uF limit. In addition it is good to keep max current within certain limit(s). This task is now given to TPS2552 (yes yet another TI part). This part provides slew rate, over current/temperature limits and is almost straight forward to use. Only almost because the current/limiting resistor value is not "straight" and has some variability. So, one needs to decide which limits (min, nominal, max) are followed. Current limiting resistor selection-visualization attached.Otherwise nothing fancy yet. Power and fault LEDs and some ESD protection.

author: voltsandjolts
author_rank: Unknown
timestamp: April 11, 2025, 07:10:55 pm
content: I like the idea of an isolator board with features suited to embedded development, but generic enough to be used in a wide range of setups. The GPIO can be used for program/debug SWD isolation, assuming isolators can handle a few MHz. Also for uart, just need to plug an ftdi cable. All with IDC/0.1" header pins is fine.Ah, ofcourseSWD has the bidirectional data line, as do other debug protocols.Where do you set the voltage supply for the DUT?

author: eleguy
author_rank: Regular Contributor
timestamp: April 12, 2025, 06:43:47 am
content: Quote from: voltsandjolts on April 11, 2025, 07:10:55 pmISO6xxx can handle 50-Mbps. ISO7xxx can do 100Mbps but I thought that 50 is more than enough for these purposes.Quote from: voltsandjolts on April 11, 2025, 07:10:55 pmYes, this has been taken into account. In the case of SWD it can be done just by shorting in+out together. They (followed link you provided) seemed to give this solution as an example as well. OpenOCD has had similar "resistor-hack" instruction already for yearshttps://github.com/arduino/OpenOCD/blob/master/tcl/interface/ftdi/swd-resistor-hack.cfgSome things are not that straight forward. Like I2C for example. But that is why such "real" bidirectional isolator is also added. Hmm, maybe it is a good idea to include some wiring examples with the thingy (if it is ever found working anywhere). However, working with the documentation is not my ...... lets say not in the top hobby/free-time things I like to do...Quote from: voltsandjolts on April 11, 2025, 07:10:55 pmThis is not yet written into stone. First I thought one could select it from the list of pre-selected voltages [ 5, 3.3, 1.8 ] by shorting some pins out (from the IDC header again). The LDO which is now on the table supports setting the voltages in "digital manner" (0.1V steps). This could be controlled from toggle switches, GPIO, counter even(?) or over I2C extender like I thought. But is it then too hard if one likes to just utilize UART? One option could be to have it analogically set by the potentiometer. Not sure yet. What do you think?

author: voltsandjolts
author_rank: Unknown
timestamp: April 12, 2025, 07:18:05 am
content: Quote from: eleguy on April 12, 2025, 06:43:47 amI like the idea of continuously variable supply voltage, say 2.7 to 5.5V (or whatever the isolators can handle), which accomodates many devices and allows for USB Vbus testing as mentioned earlier. It's not often this would need adjusted, and certainly shouldn't be adjustable accidently, as may happen with a larger potentiometer. My preference would be for a 10-turn SMD potentiometer that needs a small screwdriver to adjust. The 10-turns allows good precision on voltage setting and prevents accidental slip of the screwdriver over-volting the DUT.Edit: Also a pair of circa 1mm hole testpoints on PCB, so you can easliy hold DMM probes there while setting voltage. Or better still a pair of those 2mm PCB mount sockets would be nice, to plugin in the DMM probes.Edit2: An IDC connector to plug-in a Segger J-Link would be nice too, but that's just me

author: Nominal Animal
author_rank: Super Contributor
timestamp: April 12, 2025, 07:53:50 am
content: For low currents, say 500mA or less, I think linearly regulating 7V–8V down to 1.8V–5.5V should be acceptable, assuming you have large enough heatsinks. You might have a few fixed regulators in series, each dropping a couple of volts, with an adjustable one in parallel with each fixed one, spreading the waste heat generation; although the range for each adjustable regulator would be limited to some overlapping sub-ranges –– say, one could be 1.2V – 2.4V, next 1.8V – 3.0V, next 2.8V – 4.2V, next 3.8V – 5V, and last 4.5V – 5.5V. You get the picture.The other option is to have a DC-DC converter to about one volt above the target voltage, a capacitance multiplier or CLC filter, and a low-dropout linear regulator afterwards. I've wanted to look into this, especially using one of the cheap but high-efficiency switchers suggested by TI Webench (for say up to 2A currents), but such controlled preregulation is outside my electronics-fu.

author: eleguy
author_rank: Regular Contributor
timestamp: April 12, 2025, 10:08:25 am
content: Quote from: voltsandjolts on April 12, 2025, 07:18:05 amThere will be isolator independent power conversion with VDUT support 1V8 -> 5V5. Variability is either continuous or with some "steps". Will see.Quote from: voltsandjolts on April 12, 2025, 07:18:05 amThis is a good idea. Somehow I still would like to have an option to set the voltage and know where it is set (also) without having DMM. Maybe some "hybrid" model. Will come up something and post it under comments...Quote from: voltsandjolts on April 12, 2025, 07:18:05 amI don't want to make isoprojkt bound to any particular "proprietary" HW but maybe little adapter to the rescue? Not hard at all to make such and would not cost too much. It is only wiring x to y and having correct connector. Remind me if I forget it on the way. Reminder link addedhttps://www.segger.com/products/debug-probes/j-link/technology/interface-description/EDIT==Haha!! Thought to survive with 2 port HUB but no no... This discussion got me to understand that the optional stuff can be inserted into host side as well. This way gadget zyx gets also protected by the isoprojkt. Certainly it could be used without extra USB port but then one should stick this extra gadget directly to the computer(host). Maybe it is more handly if the gadget's USB can be connected straight to isoprojkt?

author: eleguy
author_rank: Regular Contributor
timestamp: April 12, 2025, 10:54:54 am
content: Quote from: Nominal Animal on April 12, 2025, 07:53:50 amMy idea is (currently) to support (lets say) 500mA (or even more) when plugged into host only. In this case power comes from the host through isolated DC/DC conversion. When user connects an external power source the DC/DC converter is switched off and isoprojkt enters "silent mode" where only LDO(s) are utilized. There should be support for higher current (1A?) in this mode. Having a heat-sinked pre-regulator in place there would be room to play around. Lets see... Posting more about this once I get "first-things-first" done.Quote from: Nominal Animal on April 12, 2025, 07:53:50 amWhen high currents and somewhat low noise are required then DC/DC converter as a "pre-regulator" is the "scheme" I typically design. With careful selection of the LDO and the filter components one can get pretty good results. Overall it is not so hard to filter the output when all parameters are known. What makes it hard is the variability of V_IN, V_OUT, I_LOAD, allowed V_DROOP and the target noise/emission levels. (not now claiming all would apply in this case).It is not hard to find schematics having badly selected parts. Typically people just stick here and there "something". An example, pushing in "some" LDO after DC/DC converter. Typically what happens is that the PSRR of the LDO is somewhat low at the frequencies where it would be needed. Or it fails to filter those critical frequencies under some specific current which now happens to be the most used (average) level where system is working.Anyhow, I thought to add two things into one. Low noise and isolation and there I don't see room for DC/DC conversion (case external power) with this low currents we are talking about. Does not just pay back. Rather push the money into slightly better LDO.In isoprojkt preselected DC/DC converter (case power from host) has Fs=400kHz. At that fundamental frequency the preselected LDO TPS7A47x (4uV rms) has over 50dB PSRR (and more at 3rd harmonic) @somewhat low dropout/over wide range of I_OUT.However, this raises a question. It would not be that hard (take out from the DC/DC conversion but costs bit more) to have also negative VDUT. Not that much power but just for low noise biasing and enough to power opamps and so. I could see use for such but do you? And does it fit into this concept? Also bipolar external power supply would be then needed if one likes to utilize the "silent mode". Well, user does not have to push in negative rail but then VDUT- would just be zero having still VDUT+ as discussed so far.

author: eleguy
author_rank: Regular Contributor
timestamp: April 16, 2025, 04:26:27 pm
content: Pseudo-random isoprojkt update / trying to get rid of the flu.Spent some time with some sanity check simulations. Base don those the SN6505B seems to be reasonable selection but the transformer ratio had to be tuned a bit. Würth 760390014 (1:1.3) looks somewhat ok-ish for the intended use. As a result of changes, there will be less current available at high end of VDUT (5.5V) than thought at the first place. Still conservative amount (~150mA) and this limitation is (only) in the case where external PSU is not attached. But when VDUT is not more than 5V then one can utilize already 250mA. This behavior goes hand in hand with dropping VDUT requirement up to 400mA(+), Maybe not so bad after all? Transient response should be calm and clean. Specially after LDO.In addition I made some first simulations around TPS7A47 which do show that it should work as marketed. However, one has to bargain a bit the from noise level (still having low but not ultra low). Specially, if you like to push up to 5V5 and "max" current. Again, there is no such limitation with the external PSU where all should be "whisper quiet". (yeah, right).One fancy way to set the voltage could be "expert"-mode where one makes the setting (instead of rotary) with dip switches. This way output would be settable from MCU as well by "hand". Output voltage of TPS7A47(x) can be set anywhere from 1.4V with 100mV steps. The dips would look likeBASE 1.4VDIP 1, +100mVDIP 2, +200mVDIP 3, +400mVDIP 4, +800mVDIP 5, +1.6VDIP 6, +3.2VFor example setting 3V3 would happen by 1.4+1.6+0.2+0.1=3.3VSo, in addition to isolation one would train some basic math skills. Not sure if this feature could be counted as an advantage or not... eh. Is this too weird?

author: eleguy
author_rank: Regular Contributor
timestamp: April 17, 2025, 05:23:52 am
content: Quote from: Nominal Animal on April 02, 2025, 09:37:11 pmDo happen to know a switching frequency of these devices? And, do they utilize same over all similar models? Maybe I missed that. If it is unknown or not mentioned anywhere then (just for interest) could you measure it from the model you have? Measurement under some load (300mA?) and without is also needed to see if converter has some PFM mode or not.

author: eleguy
author_rank: Regular Contributor
timestamp: April 19, 2025, 09:57:54 am
content: Mostly-random isoprojkt updateTrying to settle into some VEXT (=isolated external PSU) max voltage in relation to the DUT output current that the isoprojkt would support. It is mostly power dissipation "issue" and how to deal it. Having DC/DC conversion was ruled out by the low noise option that the VEXT should bring. Well, most external PSUs will(?) be some sort of switching ones which means one cannot control so well the input noise level. This worries me a little. So, I decided to make some guiding visualizations around the PD matter. First and maybe the most simple one attached. Here one sees (which is evident) how much dissipation there would be in the worst case. Blue is easy to manage, green is doable and yellow/red needs additional stuff around what was though at the first place. Note. Numbers are not big but there are many thoughts/initial constraints behind that do make these limits to realize.EDIT :: added working area, VEXT, VDUT / PD image

author: Nominal Animal
author_rank: Super Contributor
timestamp: April 20, 2025, 01:03:40 pm
content: Quote from: eleguy on April 17, 2025, 05:23:52 amAs I've used these to power single-board computers, with their own internal filtering regulators, I don't know much beyond their datasheets, and that they seem to be good quality versus price power supplies; I've certainly been happy with them.I currently only have aGST60A05-P1J(5V 6A) at hand (for my Odroid HC1), but no suitable programmable load, and only an Analog Discovery 2 as a measurement device 😢..

author: eleguy
author_rank: Regular Contributor
timestamp: April 21, 2025, 06:00:41 am
content: Quote from: Nominal Animal on April 20, 2025, 01:03:40 pmSuch can do as a load in this case. Or, one could stack some resistors to make some. It does not have to be too "scientific".Quote from: Nominal Animal on April 20, 2025, 01:03:40 pmMy friend has same gadget and he always carries it with him. Seems to be a handy low weight tool that comes with the FFT function build in (SW). AD2 BW should be more than enough to show up fundamental switching frequency of such PSU.But don't worry. I was just curious and can proceed without.

author: Nominal Animal
author_rank: Super Contributor
timestamp: April 21, 2025, 02:30:15 pm
content: It can be a bit difficult to say what is from the spiky load (like SBC) and what is from the supply, which is why I'd prefer to use something like a 15Ω power resistor (likethis 15Ω oneorthis 4.7Ω onefrom Partco, for 3V – 9V supply testing). I think the spectrum above a few MHz is that interesting (and therefore AD2 would suffice here), because high frequency noise is so easily filtered out with low-pass passive filtering and even bulk capacitance, to the levels acceptable to any digital circuits like the USB stuff we're talking about here.Odroid HC1 itself is very "spiky" as a load in particular. Additional stabilization (capacitive multiplier, lots of bulk capacitance, possibly following a CLC filter) definitely helps when using a spinning-rust SATA drive or an USB powered 3G/4G/5G/LTE modem: it has a built-in SATA port, one USB 2 port, and a gigabit Ethernet port, and a Samsung Exynos 5422 octa-core processor, similar to venerable Odroid XU4. Later versions of the SBC incorporated a buck converter. Current version,Odroid HC4running from 15VDC (14.5V – 15.5V), recommended 4A max, although typical average load is just a few watts (16W when serving files via Samba).For the next router/firewall/4G/5G/LTE modem thingy, I'm looking at Radxa Rock 3B, which supports USB PD (including the typical 20V fixed).I'm interested in providing low noise isolated DC supply to the isolated side, because I want to avoid all the stability/glitching issues I've seen with HC1 during the years. HC1 really needs a 5V supply with lots of bulk capacitance at the DC input jack to be stable; but then it reallyisstable. I even did my own measurement board based on Teensy LC (sitting on top of the HC1) to verify this. USB itself only allows 10µF, and that just doesn't cut it when you have very noisy devices like OLED displays on the same supply (although fortunately one can use a dedicated 3.3V regulator followed by bulk capacitance for the OLED display alone). To me, using a class II isolated supply providing say 7V, filtered and linearly regulated down to 5V, provides a much more robust 5V rail (including much larger capacitance/filtering), and thus can paper over USB device design bugs. A typical such bug is using an OLED display powered from the same 3.3V digital supply rail, and an ADC with analog supply derived from the digital supply rail using only a ferrite bead and a 1µF capacitor. The OLED display current draw is so "spiky/steppy/switchy" itwillaffect those ADC readings; the ferrite and small capacitor just isn't sufficient there.

author: eleguy
author_rank: Regular Contributor
timestamp: April 21, 2025, 04:35:34 pm
content: Quote from: Nominal Animal on April 21, 2025, 02:30:15 pmTrue.. one-shot measurement is hard without (fully) resistive load. But difference is the key in many cases. But yes. It needs more patience and sometimes an "sharp" eye.Quote from: Nominal Animal on April 21, 2025, 02:30:15 pmisoprojkt will have USB in some sort of complementary and yep... there noise is not often the issue. However, I am currently targeting the design to "somewhat" low noise levels. It does not increase the total cost so much and as a bonus then I have some tool I have missed at my bench. Low noise levels are interesting in general when powering/testing some noise sensitive non-USB thingy (ADC, DAC, RF amplifier,...). My bench supply is not that noise free. For really low noise stuff I have used batteries and metal enclosure which has coax connectors.Quote from: Nominal Animal on April 21, 2025, 02:30:15 pmLooks good for most use cases. Somehow I have ended up to over-engineer stuff in this area as well and therefore need more ports. I use OPNsense but don't now remember which Swedish e-store I bought (supported) HW for it.Quote from: Nominal Animal on April 21, 2025, 02:30:15 pmTrue, that is the capacitance seen instantly when cable is plugged in. Standard wants to minimize the inrush to something. They specify 120uF upstrean which should manage 10uF dowstream easy as what. Just place some sort of current/slew rate limiter thingy and you can have as much capacitance you like.Overall I think you are scratching several things. I agree mostly but maybe just not able to visualize what you like to accomplish. Would you like to fix the device you have, make such but just better or just as interested to find and learn? Or something else?

author: Nominal Animal
author_rank: Super Contributor
timestamp: April 21, 2025, 08:35:44 pm
content: Quote from: eleguy on April 21, 2025, 04:35:34 pmWhen investigating devices, I'd like to make it easier to pinpoint possible sources of problems, and separately eliminate them.Long-winded detailed explanation:The UART isolators I already use to connect to SBC serial consoles allow me to use the SBCs original supplies. If there is any kind of issue, say even just occasional RAM data errors, I can compare the behaviour between original and known-good supply, and thus possibly exclude the supply as a problem. But that requires I can observe the operation with both a known-good and the original supply; only the known-good doesn't suffice, because replicating a problem is often nontrivial.The way I want the isolated side supply to be grossly overpowered (to around 5V 6A, say), is directly related. Some loads, like early 3G USB modems, werehorriblyspiky, drawing up to 2A spikes from the 5V USB supply. Devices like spinning-rust 2.5" HDDs draw a lot of current when spinning up; so do devices on startup with lots of bulk capacitance; many practical devices completely ignore the USB inrush/capacitance limits. Instead of a brownout or current limiting kicking in on a short spike, I want the supply to be able to handle it, and only kick in when prolonged. That is also where the MCU for monitoring and reporting comes in.In a very real sense, it is all about modularity as an approach to problem solving. I want to be able to change a single part, whenever it helps me pinpoint any issues I might see. I also want that changing to be simple and robust, not worry about ground currents (that have bitten me before) due to devices being powered from different mains AC circuits and their AC/DC conversion yielding different/incompatible 0V "GNDs", which is why I use isolators and not a lab power supply/supplies with 0V/GND common among all devices.Even when developing and debugging software, I follow the same approach. For a new system, I approach simultaneously from the top down –– to get a picture of the interdependencies and subsystem boundaries and expectation –– and from the bottom up. One part is modeling what the designers and developers thought the system should do, and another part is modeling what the code actually does. Bugs are often found whenever the two disagree. (It is also why I hate the "throw spaghetti at the wall and see what sticks" -type of aggregating different code snippets blindly together until the output seems to be what is wanted; and why I do not participate in any discussions involving LLM/GPT hallucinations about what a solution to a problem is. That kind of trial and error without any overarching design ischaotic, and is better rewritten from scratch immediately when sufficient information on what the desired outputs for possible inputs are, and what outputs are acceptable for unanticipated inputs.)For my own code, I implement unit test cases of the key algorithms and code "modules", but not in a library form: they are prototypes, like fully-featured examples, or pluripotent code tumours, that I adapt and shape to each use case by trimming off all the excess, via apoptosis. It is not exactly code reuse, and not exactly reinventing the wheel, but a middle path stealing the principles from natural evolution, you could say.As I am only a hobbyist on the electronics side, my schematic designs seem to follow a similar trajectory: I design some modules, combine the modules to produce a device with the features I want, then testing and pruning down to the feature set I actually find useful in practice.When developing or testing new circuits, I tend to always have an MCU with native USB capability for a number of reasons, but the biggest is personal preference, second biggest use cases. Then, the USB isolator protects me from my uncle bumblefuckery, stopping any damage at the USB isolator, keeping my expensive computers safe. That also relaxes me, and leaves my meager cognitive powers to focus on the work at hand, and not on e.g. what damage might occur if I accidentally drop a screwdriver across the power buses or something like that. (Even shorting VUSB +5V to external +12V supply can easily fry your USB A ports. Even though the fried chip is a cheap one (say ESD diodes or the port/hub current control chip), finding which one it is and replacing it is not cheap.)The external isolated 7.0V – 7.5V DC supply (7.5V nominal before filtering) is at the very core of my design. Because it is well over a full diode drop, and over low-dropout linear regulator drop over the USB voltage range (4.5V – 5.5V), my power flow is always from higher to lower voltage domains, no exceptions. In USB designs, especially when an isolator is involved where both sides need their own supplies, the power must not be allowed to flow upstream, device powering the host: if the two supply voltages are almost the same, noise flips which one is higher, and chaos ensues.For TI ISOUSB211 each side needs a maximum of 16mA at 5V or 3.3V, plus up to 96mA at 1.8V; for ADuM3165/3166, up to 69mA at 3.3V. Isolated DC-DC converters are typically 75%-80% efficient at 10%-100% load, but do require a minimum of 10% load or the output voltage can rise well over double the nominal voltage, and tend to have quite a lot of conducted and radiated noise, requiring filtering; but even assuming perfect DC-DC converters, those are 0.226W and 0.228W, respectively. With typical circuits, say around 0.320W. Using just linear regulators from a nominal 7.5V rail, the power draw can be up to 125mA per side for ISOUSB211 and up to 70mA per side for ADuM3165/3166, so about 1W and 0.5W, respectively.The question is, is the difference between 0.3W and 1W for TI ISOUSB211 (using capacitive isolation) worth the component count and switchmode noise?ADuM3165/3166 uses iCoupler tech (magnetics), and the electromagnetic radiated noise is probably on the same order of magnitude with or without an additional DC-DC converter.For me, the answer is to use simpler linear regulators, prefer ISOUSB211 (capacitive) over ADuM3165/6 (iCoupler), and deal with the waste heat using large cast-aluminium enclosures as heatsinks. If I use standard 5.5mm×2.1mm DC connectors, I can use the aforementioned Mean Well 7.5V wall warts.

author: eleguy
author_rank: Regular Contributor
timestamp: April 23, 2025, 07:12:50 am
content: Quote from: Nominal Animal on April 21, 2025, 08:35:44 pmThanks. I think I now better understand your way of thinking/working.Quote from: Nominal Animal on April 21, 2025, 08:35:44 pmLike you mentioned there are many kinds of "spikes". The hardest are periodically repetitive and high dv/dt "spikes" as those create noise over high frequency range. Seen typically as a result from some sort of switching. High frequency range content tends to find a resonance/antenna structure and become an EMI and/or signal integrity problem.Quote from: Nominal Animal on April 21, 2025, 08:35:44 pmI am currently designing the LDO part of the isoprojkt where INA236 or INA232 (cheaper than INA22x series) could be considered for the VDUT/IDUT measurement. These are marketed as ultra-precise gadgets but still they cannot do miracles. The smallest output sample period is 140us. Enough for many things but nothing beats (well cannot even be compared to) scope / spectrum analyzer when digging in the EMI / signal integrity business.Quote from: Nominal Animal on April 21, 2025, 08:35:44 pmCould not agree more...Quote from: Nominal Animal on April 21, 2025, 08:35:44 pmI have done and do the same.Quote from: Nominal Animal on April 21, 2025, 08:35:44 pmThis is as mentioned before one of the main drivers of isoprojkt.

author: eleguy
author_rank: Regular Contributor
timestamp: April 23, 2025, 01:06:42 pm
content: Random isoprojkt schematics update.Earlier there was some discussion and comments how the VDUT voltage should be settable. Some likes rotating the knob, one likes to make an automatized test case with the help of mcu and sometimes just a fix setting could do the trick. I spent some time thinking what is the best option for this project. The answer is THEM ALL!!First it might sound like a feature creeping which ends up having a huge BOM. Let's see... The voltage setting mode (fixed, adjustable, I2C) is toggled by one switch (S2). The other switch (S3) acts as a fixed output voltage selector and is in the game only when "FIX" mode is selected. In the I2C mode VDUT output is zero until the I2C GPIO extender kicks in by setting the voltage (1.4V + corresponding step) and enables the LDO again. FIX mode has currently voltage levels (1.8, 3.3 and 5V) I use mostly but these can be still altered if better set is found. Anyhow, you can set the VDUT to anything from 1.8 to ~5.6V with rotary a potentiometer.User can monitor VDUT and IDUT (and even do some power monitoring) with the help of INA236 but is not forced to. This also works over I2C. And as the name of the project says over isolation.Don't take input/output capacitance of the LDO too seriously yet. Now drawn caps work more as a space keeper. I will still try to simulate to find out what is actually needed. Might end up putting "just for sure" caps as those can be left away if not needed.Any comments are more than welcome!Same pic in png and pdf format attached.

author: eleguy
author_rank: Regular Contributor
timestamp: April 28, 2025, 08:50:47 am
content: Some isoprojkt update...Simple isolation idea has got some flesh around the bones and become ... a mess?? Many of the though "submodules" are more or less done. Some work to do with the connector (access/dut) areas as well in big picture sanity check. Somehow I am not (yet?) too happy with the mid-outcome. When stepping back it does not somehow feel a complete "tool" or something. Not sure.Anyhow, isoprojkt has now own internal I2C bus to prevent any potential conflicts with DUT(s). One can see dashed line in the "Digital isolators" module. Lower part is meant for isoprojkt internal only and upper part for DUT. From the access control one can now utilize connections as follows2 x bidirectional (like for I2C)7 x input DUT -> Access8 x output Access -> DUTReason for this is the level conversion and what extra was provided by the bidirectional isolator.One "new" feature was added. DUT can be now self powered. In this case isoprojkt will sense the used VDUT and make a buffered copy to power up isolators (isolated side). This way isoprojkt does not draw power from the DUT.Attached the big picture (it is not finished)...

author: eleguy
author_rank: Regular Contributor
timestamp: May 02, 2025, 12:41:55 pm
content: Random updates do continue...I might have found my way back from the endless sea of connectors. First place I though the IDC header/cable/socket is the way to go. Affordable, easy to get and usable even without mating connector. Then I thought there has to be a better option. Why did I think so? Regretting... Many, many hours wasted while browsing the options available. And this is not the first time nor first project I get lost with this. It would be easier if someone just told me to "use this" and my share was to implement and whine someone else's decision. But there are so cool board to board, board to socket whatnots.... Blaah...Anyhow, 34 pin/position rectangular IDC "system" seems to be (again) something that could be considered. I happen to have those available as well those can be bought from here and there. It is many pins but now one can also slam in many "stiff" reference "plane" wires (like 0V, 3V3, ..) between toggling signals. And it should not be impossible to get USB2 over such for a short distance even it does not fully comply with the impedance. In worst case I will to some matching. However, I don't think it is needed as similar method is utilized on the MBUs.Just listing here as an example what kind of parts I mean (digikey part numbers, in 100 quantity)H3DDS-3406G, ~0.91EUR, 34 pin IDC cable, for extending stuff further away from the connector. Would be only used on the DUT side (case by case).SFH11-PBPC-D17-ST-BK, ~1.07EUR, 34 pin Female Header connector, for access extension/adapterBHR-34-VUA, ~0.32EUR, 34 pin male "box" header, un-isolated and isolated side.

author: eleguy
author_rank: Regular Contributor
timestamp: May 06, 2025, 08:32:41 am
content: After finishing the missing links and some minor changes the Kicad's ERC (Electrical Rules Checker) is happy. The design has no more errors it says. However, one cannot be yet too satisfied as this does not tell so much...Next I will do a sanity check for every module and fix found unwanted "features". If everything still makes sense then it this time for the BOM optimization and component "matching" against the fab-house's component gallery. I typically ask the fab-house to mount all cost effective and smallish (like 0402) parts. Specially if there are several of the same kind. I tend to do this check and decision before routing the board. It is just easier to change particular part / footprint now than after routing.There are also some parts (mainly pots and switches) which I have not decided or happy with the found one(s) yet. The SP3T switches in the current design are now from e-switch (EG1315AA). Those are somewhat small. Maybe too small for this project. There is also THT (just take "AA" away) version available. I don't have experience from either and would like to find a switch/pot which works as well "feels good".Current big picture attached. I do design in the "dark mode" and these exports are made in Kicad default(?) color scheme. Therefore colors may look sometimes as non-optimum choices.

author: eleguy
author_rank: Regular Contributor
timestamp: May 10, 2025, 12:35:23 pm
content: isoprojkt is ready for routing... Sanity check revealed some stupid mistakes. After fixing those and making the missing footprints project is ready for routing. What happens next is that I scratch-layout module areas and place them next to each other. As the result one can see how big area is actually needed for the components. Then hand in hand think and re-iterate the initial placement with the enclosure candidates (or DIY custom 3D design, lets see).It is somewhat certain already now that the initial LEDs will be replaced. Maybe something else as well. The pots have to be somehow "embedded" as they look bit too high when mounted like they are in the "auto-placement" picture (see attached file). Hmm, what else... Ah, connectors got changed to even more pin ones. Now the pin order "matches" Raspberry Pi pinout. So, those are compatible at least with something.Auto-placement takes 120x120mm space. I would like to get isoprojkt fitted into 100x100mm in order to get the board through the most affordable (JLCPCB) fab-house process. Not mandatory but as some sort of target. However, it might be difficult as some components do need reasonable PCB area in order to dissipate designed heat load. But lets see how things get forward.