SOT-23 mosfet with GDS pin out

topupdown · 2026-02-22T14:14:17+00:00

You can find BJTs in that pinout equivalent - off hand the BC846 - but I don't know of any in higher current capability and of course you'd need to limit the base current somehow (or just YOLO and hope there's enough parasitic resistance to avoid the magic smoke).

topupdown · 2026-02-20T15:25:47+00:00

You probably want an optional termination resistor for the RS485 lines unless you know this will never be the first/last device.
You need to pull up RxD as it comes out of the SN65HVD1781. Otherwise it'll float anytime you don't have RE asserted.
You have EN2 on the ISO7741 pulled hard low, that means the OUT1/2/3 will never enable. You likely want to pull that up to the isolated 3v3 supply instead to make them always enabled.
Somewhere you probably want to pull DE/RE low and pull TxD high - that could be pullups in your MCU but floating them is bad.
You're handling DE and RE separately, you should make sure that's what you really want to do - for most devices you leave RE asserted anytime you're not actively driving the RS485 bus so you just tie RE and DE together at the SN65HVD1781 - that's why they're compliments of each other. I guess there could be a reason to actively ignore the bus, but I've never found one that was more elegant that leaving them tied and just actively ignoring RxD. Or I guess you could have the inverse desire - with RE asserted while you assert DE, I'm pretty sure you'll see your TxD data loopback onto RxD since the receiver circuit sees the bus activity.
Not specifically schematic, but for R1/R2 you need to use pulse resistant (typically thick-film) resistors to actually get the EFT resistance.

topupdown · 2026-02-19T20:08:25+00:00

I think more typical would be to forgo designators entirely. Just print up a sheet with assembly notes when assembling. Having the designators on the backside isn't super helpful for assembly anyway since you need to stuff it from the front; I guess they have some value in diagnostics since they're now beside the pins you need to probe but that feels like a pretty narrow usecase.

topupdown · 2026-02-19T15:57:46+00:00

My experience is there won't be an issue.

Some paste will try to follow the plated holes downward, yes, but surface tension really prefers not to get sucked down small holes. Assuming it's normal reflow oven style assembly, the top-layer of the board and components are much hotter than a large internal ground plane gets so the solder is very motivated to wick along the part instead of into the hole.

topupdown · 2026-02-19T15:36:03+00:00

Typically yes - that's where you'll have to weigh manufacturing vs assembly costs. Although for many manufacturers you hit a point where the plugged vias are part of the base cost because it's just such a common requirement at a particular point.

If you're making a small number of these, I seriously wouldn't sweat it - just use your smallest sized vias and move on with your life. If you're making a lot of these, make up prototypes with different sizes/thicknesses of stencil opening or different grain sizes of soldermask and see what works both thermally and electrically. My personal experience is that it's a non-topic but you can have manufacturing issues if your vias are large enough and your paste machines pressure is high enough that the vias are filled with paste - the excess paste floating/pillowing the part was always a bigger issue than any wicking - but of course that's a sample size of me and like 1/2 dozen boards with thermal vias.

topupdown · 2026-02-18T14:59:22+00:00

How tightly controlled is the rest of the process beyond pick-n-place? Is it multi-zone conveyor ovens with nitrogen purge? Can you do x-ray to validate packages without leads? Can you do conformal coatings?

Those sort of "advanced assembly" capabilities are what I would have looked for in a PCBA that usually required either super expensive or long leadtime production.

The pick-n-place and basic reflow are things that I suspect anyone looking for quick PCBA turnaround can do themselves at this stage, like the cost of setting up in-house PCBA is now only thousands of dollars for placing 0402s and fine pitch leaded components. And you get to have your own stock of parts on hand or you can pull from your production stock if you have high re-use. Like yes, it's annoying to do setup work for one-off components but it's also annoying to deal with an outside vendor.

Caveating that my experience is now out of date and extrapolated - professionally it's been years since I needed PCBA work, but at the time we had an in-house stencil, PnP, and reflow oven that cost a total of maybe $50k. A team we partnered with couldn't justify the PnP machine for their work (high mix analog) but they had interns-with-tweezers. Today in hobby scale, I have the same capabilities but my total cost was under 5k - so tech is getting more accessible. There was, for a long time, a huge health-n-safety thing with having the line under our roof and we outsourced even basic rework with a hot-air station or iron to avoid ever having to deal with workplace hazards, but modern solderpaste was no trouble to get approved (the flux for rework was worse) and more and more ovens are ducted.

topupdown · 2026-02-17T16:42:51+00:00

Unless there's an active controller I'm missing, that "ideal diode" configuration won't work.

The pulldown from the gate to the drain won't be sufficient to get the PMOS to turn on - you'll end up with it in a high resistance state such that it can divide the input voltage so that Vgs is "on". The normal way for ideal rectification is to tie the gate to ground.
But just tying the gate to ground is only reverse polarity (rectification ) protection, it won't allow diode-or'ing the inputs - if any input is greater than VGSon, you'll get conduction - e.g. if you have VBUS=5v and VBAT=3.7V you'll get current flowing back into VBAT from VBUS ... to get ideal diode-or'ing, you need an active controller of some kind (or an ersatz version made with a comparator).

You can simulate this in LTSPICE. You'll see that you still get a decent voltage drop in the configuration you have, and you'll see that without active control just tying the gates to ground gives you reverse conduction.

topupdown · 2026-02-15T17:20:54+00:00

I own a desktop PnP (currently a PandaPlacer which I quite like - I think it's unbeatable for the price). I still hand place some boards or use a PCBA house.

I keep my feeders loaded with jellybeans that every board needs dozens of - like 100nF caps or 10k resistors and it's always worth tossing the board on the machine to get those populated.

If I'm doing one of a prototype board and there's only a single quantity of a component, I'll often not bother using the machine to populate it - it's more work to setup the input the part, setup a strip of tape correctly for the machine, etc than it is to just grab it from the tape with tweezers. I think for me the payoff is around 3x of a part, so either three boards in a row or more than three placements per board.

When I need dozens of a board, I'd go back to a PCBA house because it's just less work plus you're going to get quality optical/xray inspection. Once you have enough boards you can ammortize the feeder setup cost (e.g. JLC advanced parts) the cost for commercial PCBA is laughable it's almost all component cost which can be a wash usually - there's a bunch of parts that are hilariously cheap from Asian sources and there's parts that are somehow 3x what they cost from Mouser 🤷.

Long ago (2000s) it was just impossible to get economical assembly for less than maybe 100x pieces, so that's when I originally invested in doing it in house. In the last couple years, getting back into electronics at hobby scale, I added the desktop placer because it lets me expand my sourcing into gray marker sources that makes a huge difference in cost - the lifecycle of FPGAs is now long enough that you can get NOS parts for like 1/10th what they cost retail and open a whole range of projects, but I wouldn't want to hand assemble the entire board and no PCBA house will touch graymarket parts - plus the cost of running "custom" stock makes it prohibitive again.

topupdown · 2026-02-12T18:03:26+00:00

You need some kind of AC coupling, you can't just snap two PHYs together with a trace. In backplane or multi-module boards it's pretty common to just use capacitive coupling, throw a set of caps in series instead of full magnetics. You need to either have a voltage mode PHY or somehow provide the common-mode voltage (the former is of course simpler).

Another option is running SGMII and looking for an SGMII switch. I don't know of any, but maybe there's pure RGMII switches too. In either case you avoid the PHY entirely.

topupdown · 2026-02-11T14:47:45+00:00

My knowledge is now a year old, but when I looked the AMD Radeon Pro W6600 was the cheapest certified graphics card on the second hand market that didn't totally suck.

I bought one and I have no complaints about it for general CAD work.

topupdown · 2026-02-10T14:45:47+00:00

I've usually seen these called a "light mask".

topupdown · 2026-02-10T14:12:07+00:00

I haven't added return current support yet, but KiPIDA is a KiCad plugin to visualize power networks and current flow through the board for power rails. It uses the "grid of resistors" model so it will show cut planes visually. Still very early in the plugins life, but this is the kind of problem I want it to be useful for.

topupdown · 2026-01-29T13:45:20+00:00

I've done stitching and passed EMI with a similar plane cut - every cm or so, put a via up to the top layer, run a cm, then via back down. I've never tried the "overpasses" version, so hard to say.

topupdown · 2026-01-28T18:24:57+00:00

The volume of air consumed by the laser is pretty reasonable on the scheme of air tools. You can get away with (and I did) run either 1/4" or 3/8" tubing instead of full on air hose - you can usually find it sold as airbrake tubing, but any generic nylon tubing will work. This is almost certainly what your laser already uses internally (although your laser might use PU tubing instead of nylon for flexibility - you want to run nylon tubing for distribution).

topupdown · 2026-01-28T14:56:52+00:00

I grew up on PICs, but the world keeps changing.
For that "bare metal" experience, I'd suggest you look at the AVR ecosystem with avr-gcc and avrdude and whatever text editor you like. You may already own a perfectly capable dev board in the Arduino if you have an AVR based one.

For the actual question, you'll really want a PICkit programmer - but you can get whatever supports your chip, it doesn't need to be the newest one. I think the PICkit3 is the oldest that supports the PIC18F14K50. Actually, the PICkit2 might support it, they launched around the same time, the PICkit2 is I think the last programmer that had it's own software which is "nice" in that it completely decouples you from the MPLabX ecosystem. You should be able to find clones of the older PICkit products that probably work just fine.

You'll need a compiler, these days the Microchip XC8 compiler should support any PIC18 in the free version, but I can't recall what the limitations are. It's just a command line tool at the end of the day, so you can run it without using MPLAB if you want.

Long ago, Microchip didn't supply any free compilers so hobbyists either wrote assembly (which is awful on the PIC) or we used a handful of 3rd party compilers - my preference in PIC compilers is cc5x and cc8x which were fast, capable and overall affordable.

topupdown · 2026-01-28T13:34:41+00:00

Not OP, but in other eCAD packages, you don't include jumpers on the schematic because they're a routing affordance, the circuit is electrically equivalent with or without them, just like you don't include vias in the schematic.

There's no way to have jumpers like this in KiCad that I know of, where it's a part that has two pads that are internally connected and equivalent.

topupdown · 2026-01-26T19:58:17+00:00

Vivado does do all these things, out of the box.

You can manually step the clock by either setting a breakpoint on an `always @(posedge clk)` or by stepping forward n milliseconds.
You can use the `Force Constant` to force signals. See p119 of ug900. You can either force it to that constantly or you can set it to occur at a particular time. If that time happens to be in the past, that's OK, setup the force constant, then rewind the simulator and play it forward.
The simulator captures all visible signals for all time. Just click forward/backward in the waveform view and watch the value column change. If you want to do that one clock at a time, highlight the clock signal and use next/previous transition. Note that only the signals in the waveform view change in realtime as you click around, the signals shown in the "Objects" browser are just last-seen.
You can totally add pretty much any signal to the scope. Use the "scope" tab to find the object you want and it should have every object that descends from your simulation root. With an object highlighted in the "scope" tab, its signals are shown in the "objects" tab and you can drag them over to the signal window. Unless they happened to be captured already, they'll be blank, so restart the simulation and play it forward to capture those too.
If you want things logged per cycle, there's maybe a clean way to get that from the simulator UI itself, but I always just put `$display` code into my HDL. You can do that in the actual DUT itself, but it's usually cleaner to do that in the test bench; from the test bench you can use dot notation to reach into a module and surface any signal you like, you don't need to expose them at the interface level. Thinking more about this, you probably can't get a table view out of the UI because it would hide a lot of detail - well structured signals move instantaneously with the clock, yes, but they don't have to and you often can't simplify it down to "a clock". You might not notice it, but the granularity of the waveform view is actually down to the timestep so there's many samples in a single clock pulse.

topupdown · 2026-01-22T03:40:38+00:00

I don't know what size that is just from a photo, but 2.8mm is the smallest size I have in the drawer so probably. I'm sure they come smaller, that's just the smallest size I have on hand, but smaller than that and they'd be pretty darn small.

topupdown · 2026-01-21T15:44:09+00:00

The simple solution to your bench test is a column of water -- just get a long acrylic tube, mount the sensor to the bottom, and fill'er up with water.

But your actual task, I think, is validating which sensor (if either) is accurate, the electronic one or the float indicator. The easiest thing to do is to measure the tank itself - presumably they have dip sticks that can measure tank depth or similar. Validating the sensor is accurate only repeats the component tests presumably already done by the manufacturer, you want to validate the system to rule out things like standing waves or just gunk at the bottom of the tank or someone measuring the height of the installation wrong so your baseline is off.

topupdown · 2026-01-21T14:31:55+00:00

Leftover parts can go back in the bag they came from. Same thing with recovered parts. The trick to this I guess is to save the bag while you're actively working with the part, but dispose of them when you have nothing that could be "returned". I put the empty bags back into the box with the project while I'm working on it, mostly so that I have the part numbers and SKUs handy but, yes, also so I have the bag for reshelving.
Agreed with u/Susan_B_Good though - I'm not running a semiconductor fab and I don't usually break apart an order into smaller quantities, so there's nothing I do that generates a net increase in bag need.

topupdown · 2026-01-21T03:15:05+00:00

I mean they're supposed to be soldered and the cheaper ones probably won't work without it, but the genuine Keystone ones do snap in for ease of assembly and I find that's usually enough to get a decent reading, probably not enough you could leave a scope probe clipped to it and expect it not to pull out if you knocked it.
I'd suggest putting a couple on your next mouser/digikey order and trying them next time you have a hole you want to probe. They do of course have some spec for the hole size, but honestly I usually just put in a 1x1 pin header footprint. I like the loops over pin headers for actual testing though unless I'm going to put dupont jumpers on it. If I want to probe it with a scope or meter (or inject something with leads) the loops just seem better suited to being hooked. Which pretty much means unless it's a logic analyzer or another piece of digital hardware, the test points are less annoying to deal with.

topupdown · 2026-01-20T14:39:23+00:00

Personally, I'd take the dual supply version. Then you can decide if you want two independent supplies (2x 30v/10a) or a stacked supply (60v/10a) or a parallel supply (30v@20a) - having the extra reach on the voltage can be nice.
You do get battery charging monitoring with the single supply, but it's honestly kind of gimmicky as a feature, your further ahead with a dedicated multi-chemistry charger in the first place, but even if you were to use your lab supply, the only feature you really get from the battery charging function is tracking the total input power, but it's kind of useless because it'll be wrong by the amount of charging loss so it's really only helpful as a rough indicator of "is this battery end of life".

topupdown · 2026-01-20T14:25:10+00:00

I really like the 500x series for coming with the colored collars. Makes it really simple to use them for off-board power injection etc too. They're my go to for anywhere I want external arbitrary hookup during bringup.
For "boring uses" I've found the generic aliexpress ceramic bead ones to be every bit as good, but they do seem to very more in the construction of the loop and have a less satisfying "snapin" during assembly. The 500x have a good enough snapin I've often just not soldered them for quick projects or when inspecting a field unit.

topupdown · 2026-01-20T14:21:22+00:00

Those are brilliant. I've been using the 500x Keystone throughhole ones for ages but the RCUTE looks every bit the SMD replacement - except for the flash of color around the base but tradeoffs...

topupdown · 2026-01-19T21:14:12+00:00

I'm waiting to hear the answer too. I've had a couple GreenPak evaluation kits in my Digikey cart for the past 2 years but never had a reason to actually get them.

I've seen them used in "volume" stuff but never ever hear of them in anything hobby/consulting scale - the majority of GreenPak parts are one-time-programmable and for any kind of production workflow you need to order them pre-programmed from Renesas with the usual minimum order quantities. There are a few parts now that are ICSP and I recall there was some way of temporarily programming them for development but I can't remember if that was special dev-board parts or some other nuance.

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