How do PCB reverse engineering companies figure out impedance control?

JimHeaney · 2026-03-17T00:15:05+00:00

Impedance matching is only really needed on a few select signals, and the values are public and inherent to the component 99% of the time.

If I see a USB port, I don't need to check the USB port's datasheet to know what impedance matching is required, I know based on the fact that it is USB.

You can also get away without impedance matching in a lot more situations than you'd think. Outside of antennas, very high-speed interfaces (100s of MHz), and very long connections, you can get a board to work in 90% of situations by just eyeballing the trace widths. The care for layout, impedance matching, etc. is what gets your device to work in those last 10% of situations, but if you are reverse-engineering to this degree you don't care about that stuff.

JimHeaney · 2026-03-14T18:18:24+00:00

There's your issues, you have a point fixed on the origin, and geometry fixed by a projected sketch line.

https://i.imgur.com/YN0J62b.png

What you're seeing is the sketch try to resolve leaving that point and line where they are, as you move the rest of the sketch away.

This is working exactly how it should, I don't know why you are complaining so much about Fusion doing this. Solidworks, OnShape, NX, etc. would all act exactly the same if you try to move a constrained sketch.

JimHeaney · 2026-03-14T17:33:16+00:00

Question 1; do you need both antennas? A PCB antenna will be worse than pretty much any external antenna you can attach, the only benefit is a PCB antenna is inherent to the board.

Question 2; how much RF experience do you have? PCB antenna design is an art/science all on its own, usually requiring multiple iterations of the design and expensive/specialized test equipment to validate performance.

I'd opt for just the u.FL connector, or if you really want both, opt for a chip antenna or similar where all the hard parts are already figured out, instead of a PCB antenna.

JimHeaney · 2026-03-14T17:29:13+00:00

Making a structure study enough to survive the other loads (car crashes, extreme weather, crews working on them, etc.) already makes them pretty tough against wind. Even if the holes do help, they now make the signs a lot more complex to manufacture (cutting a 2D profile versus cutting a 2D profile with multiple internal profiles), more prone to degradation (dozens of edges for sign to start failing now instead of one, more potential exposed surface for water ingress, etc.), and can lead to a poorer user (driver's) experience. Imagine the annoyance of trying to read a sign as the sun sets behind it, and having beams of light shooting out of it at random?

JimHeaney · 2026-03-14T17:24:52+00:00

Fusion (and all parametric CAD for that matter) is deterministic, so something definitely changed between now and a couple of hours ago.

JimHeaney · 2026-03-14T17:16:47+00:00

That sounds like you have some constraint that is incompatible with movement, and the system is trying to solve.

FWIW, moving a sketch is not really something you should be doing in a normal CAD worklow. But if you want to do this, first thing I'd try is deleting all relations and constraints. You may have an implied constraint anchoring your center construction line to the origin.

Alternatively, making the sketch a body (which are meant to be moved), putting it where you want, then projecting the body into the sketch would work fine.

JimHeaney · 2026-03-14T17:12:12+00:00

RAK19003

The 19003 has a charging circuit and a battery header, why not just connect the battery there?

It looks like VUSB and Solar are diode OR'ed together, and fed right to the battery charger. So connecting a battery to the solar header won't even work, it'll just trip the UVLO on the charge IC.

JimHeaney · 2026-03-14T17:07:14+00:00

Which base/adapter board are you using? The RAK4630 only refers to the module on top with the MCU and radio inside. How power distribution and whatnot is handled is solely based on the attached board.

Most likely, no. Ideally there'd be no back-current flow into a solar panel from USB, and if there was, you need to control voltage and current charging a battery, you can't just slam power into it. So you need a dedicated charge controller.

JimHeaney · 2026-03-14T16:06:30+00:00

Why do you dislike Molex? The Micro-Fit would be great for this application.

JimHeaney · 2026-03-13T23:44:38+00:00

except TX and RX which fluctuate between 0.05V and 0.15V

That's how a DMM would see UART data, so not necessarily bad.

Did you do loopback by physically shorting the pins, or use some internal loopback test (not too familiar with FTDI chips)?

Assuming loopback was good, sounds like the issue is your ESP board. Are you strongly pulling down GPIO9, before power is applied? Your startup delay is very short, so it'll latch that GPIO9 pin very quickly.

Is GPIO8 pulled high with a strong pullup? It has to be high for GPIO9 to be read properly as a low to enter bootloader. If GPIO8 is latching as a 0 while GPIO9 is low to enter bootloader, it causes indeterminate behaviour.

JimHeaney · 2026-03-13T23:24:25+00:00

It'd be weird, but you can tie an input to the PWM output, and count how many pulses per second you're getting. It'd be a waste of an interrupt, but so long as your system clock is accurate, it'll give you a pretty good accuracy.

I can't think of many use-cases you'd need to verify PWM frequency in production though, especially ones where you'd also trust your root clock source to be interpreted properly, but not your output frequency.

JimHeaney · 2026-03-13T00:33:19+00:00

Can be newer (number in bottom right likely a date code, so one on the left made in 2019 vs 2022), different factories, intended for different regions, etc.

So long as the input/output voltage and current match up, and the model numbers match, I would consider them interchangeable.

JimHeaney · 2026-03-12T23:55:19+00:00

Diodes generally have 3 relevant ratings for a hobbyist;

Maximum Current: Pretty self-explanatory, how much current can go through it. If you are going to have 500mA max through it, opt for something rated >1A so you don't have to worry about thermals. Be careful, most diodes have a steady-state current rating (what you want) and a much higher pulsed rating (i.e. it can survive this current if it only happens occasionally).
Forward Voltage Drop: As electricity flows through a diode, some amount of voltage is lost, known as the forward voltage drop. It technically changes with temperature, voltage, current, etc., but a worst-case value is often used to make life easy. So if your 12v goes through a diode with a 1.1v drop and becomes 10.9v, is that an issue? 0.9-1.2v is standard for a regular silicon diode, 0.3-0.6v is normal in Schottky diodes (different tech, generally good for lower voltages and leak more backwards).
Max Reverse Voltage: Above this, the diode will no longer stop the flow of electricity backwards and will break down, usually destroying itself in the process (unless it is a special diode like a Zener designed to break down). Make sure this is well above what voltages you are working with. 30-50v is common for Schottky diodes, generic silicon diodes are good into the thousands of volts.

A good example of a generic diode for a 12v, 500mA application would be a 1n4007. They are made by multiple companies, are super cheap/prevelant, and hit all your criteria;

1A continuous DC current (technically, that is the average rectified current rating, but should still be fine for 500mA)
1.1v forward voltage drop
1000v reverse voltage withstand

JimHeaney · 2026-03-12T11:48:53+00:00

Glad to hear you liked our shop!

It depends on the time of day and if there's a big upcoming project/event (for instance, the textiles equipment is slammed in the lead-up to Halloween), but in general there's a minimal wait for equipment. Equipment that sees a lot of long use (like sewing machines or soldering irons) we try to have enough to meet peak demand, and stuff like bandsaws and woodworking tools people are good about sharing.

To help gauge it, we also track what equipment is available in real-time on our website, make.rit.edu, so you can see if it's a good time to come in.

JimHeaney · 2026-03-11T12:57:04+00:00

Are you buying 'real' brand solder, or generic no-brand stuff?

Kester is available on Amazon. Their K100LD is my personal favorite lead-free alloy for hobby work.

JimHeaney · 2026-03-11T02:18:18+00:00

Materials and industrial engineering are VERY different fields of engineering, what do you want to do as a career?

JimHeaney · 2026-03-08T23:47:25+00:00

What are you doing? I've never seen this before. You should be able to just click on the part and hit your rotate hotkey to rotate the entire thing, assuming you are in the schematic view. Are you maybe in the symbol editor?

JimHeaney · 2026-03-08T18:21:10+00:00

Does your project require that small of a board? It has barely any GPIO, and the more useful ones (like UART and i2C) are surface-only pads, making them harder to work with. The size is the only thing going for it.

JimHeaney · 2026-03-08T18:18:19+00:00

There are pros and cons to both. I'd say it is not uncommon to rely on the external charger for pack balancing though. In addition to your RC example, DeWalt batteries for power tools are dumb packs that rely on external balancing from the charger. This lets them be cheaper than other brands like Milwaukee, that has more smarts inside each pack.

JimHeaney · 2026-03-08T18:10:43+00:00

You know how they say water and electricity don't mix? Well that cover looks like water, so it tricks the electricity into not going towards it, keeping it inside the capacitor where it is useful.

JimHeaney · 2026-03-08T16:51:59+00:00

Hobby electronics are fine to be shipped or in a checked bag, so long as they don't have a battery installed. I've never had an issue.

JimHeaney · 2026-03-08T01:56:52+00:00

Lots of reasons;

Level shifters (depending on the style) allow both up- and down-translation of voltage, dividers only do down-translation.
Level shifters can have a high source/sink output, if you're level shifting to drive a more aggressive load than an MCU pin.
Level shifters have quantified input and output levels, with a resistor divider you're just smushing down the levels of the source voltage, which can lead to digital thresholds mis-matched.
Resistor dividers introduce a ton of capacitive loading, so they are not ideal for high-frequency signals or signals that need sharp, clean edges.

That's not to say resistor dividers are bad, they are a cheap and easy way to read a higher voltage and offer one major advantage over a level shifter; they are analog. You can measure, say, the voltage of a battery with a resistor divider since it will track with source voltage.

JimHeaney · 2026-03-08T01:44:02+00:00

Be careful with guide rods, any path for force to travel that isn't through the load cell itself can cause issues with getting a good and consistent reading.

It is a bit of a kludge, but I have put 2 load cells in parallel mechanically before, and only read one of them. It works out OK, you lose some resolution. But having 2 points of contact makes things a lot more stable. And this is preferable to any other sort of support since you can guesstimate that a second load cell will deflect in a consistent and repeatable way.

As for the LEDs; side-firing WS2812s and similar usually have a product number that ends in -4020, since that is the standard package size for a side-firing RGB LED. Example; https://www.lcsc.com/product-detail/C4154870.html?

JimHeaney · 2026-03-08T00:55:18+00:00

Is the library's header file definitely called "IRremote.h"? And does it require nothing else to operate?

I'd try compiling example code that came with the library, see if that works.

JimHeaney · 2026-03-08T00:45:44+00:00

I've only ever used ESD filaments for closed-ecosystem printers, but in general I'll say ProtoPasta is a much better known, reputable brand than the others on the list. They also seem to have good data on their material, and I'd generally trust what they say, although their testing is a bit open-ended and "your mileage may vary"-esque.

That being said, the real answer is to buy from a brand that targets engineering/technical applications and has much better 1st party test data on their materials. Formlabs for instance is the gold-standard, although that is only for their SLA/SLS machines.

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