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@hemalchevli.bsky.social

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@hemalchevli.bsky.social · last yr.

Looking for space saver high speed connectors

Mini cool Edge (MCIO) connectors are the answer.

It’s one of those things that packs a big punch in a small package. Real estate on high speed boards is very precious. Normal PCIe connectors take up a lot of space, especially if you have multiple connectors.

Not only that, you have to have a buffer zone around the connectors for the card.

This is where you can use MCIO connectors, they take up limited space and work with the latest PCIe standard. This is a great way to make your system modular and design a compact board.

These are great for saving space on the board.

@hemalchevli.bsky.social · last yr.

What is FCC part 15-B?And why should you care?

In the US, FCC regulates use of communications by wired and wireless.

There are three sections of FCC rules that are applicable for non-licensed equipment. That is you do not need a licensed radio station to use or sell these products. These are part 15 for RF devices, part 18 for ISM devices and part 68 is for devices connected to the telephone line.

Part 15 that 6 sub parts A through F.

Sub part B is for unintentional radiators. This applies to virtually all digital devices, whether it's an IoT device or not. If the device uses a clock of 9KHz or more, it fall under this definition.

Under this subpart, there is again Class A and Class B

Class A is for devices used in industrial or commercial environments. Class B is used in residential environments. Class B is about 10dB more restrictive. You cannot legally sell your devices until you have FCC certification.

@hemalchevli.bsky.social · last yr.

@hemalchevli.bsky.social · last yr.

AI for PCB design - Are we there yet?

It's no secret, software engineers are feeling the brunt of AI with their jobs.

Some are faring better than others, but more and more tasks are getting automated. Whether we like it or not AI is and is going to become more commonplace in different aspects of our life.

Should hardware designers be worried?

Or go about your day thinking AI is just another slightly better or worse auto router. It's better to embrace AI than to fight it. Let it help you be better at what you do. I’ve been trying out various AI tools for PCB.

These tools range from full EDA suits, to helping in quick design iteration, Design analysis. I still feel they are a bit long away from where they need to be. We use past experience on how technology shifts occurred, but that’s the mistake because the time for the next shift is faster than the previous one.

I’m not making any predictions. But AI for PCB is not a question of if, its of when.

@hemalchevli.bsky.social · last yr.

Do you really need that low loss material? Or FR-4 is just fine.

PCB material is not something you think a lot about when you are doing your low to medium complexity.

When you start with high speed material, it's important to select the right material for your application. It is not the case that every time you need a exotic low loss material. You can use FR-4 if your traces are small. Yes, you will get higher loss per unit length, but overall loss would be acceptable.

There are other problems with using exotic material.

If you are using a material that is not commonly used there could be manufacturing issues. Your manufacturer might not have worked with the material and it could lead to delays. Of course it's a must to talk to your manufacturer before starting the design. Or you might find it hard to find a manufacturer who has worked with your specific material.

Budget your signal losses and then decide what material is suitable.

@hemalchevli.bsky.social · last yr.

Cadence tools - what’s what

I’m recently looking in to cadence design suit.

There is so much jargon on its homepage, I had no idea what tools they have and what tool does what. They have so many products. On top of that there is AI slapped on almost every tool.

I wanted to know what tools they have for PCB designing.

Here is what I got. OrCAD is the schematic design tool that is the primary function, but it also supports PCB design. But it's for less complex designs. It also supports SPICE simulation.

Then there is Allegro, this is the complete PCB suite, All the big server boards and complex PCBs are designed with tool.

Any Cadence user here, let me know if I got this right?

@hemalchevli.bsky.social · last yr.

Open source hardware - is it just for a reference?

Today I was talking with Brandon about an open-source hardware community project.
Open-source hardware is quite different from open-source software. In software you can work on different aspects of the project and can make contributions. On the other hand, for hardware this is very challenging.
One cannot have a person working on one corner of the board and another working on some other aspect of the board.
The only successful open-source hardware community that really succeeded is the RepRap project to my knowledge. While there are a lot of open source hardware projects, they serve more or less as a reference. You could make changes to them in your own fork but pushing back the changes is rather rare. And accepting those PR especially on the PCB is even rarer.
I think there can be multiple people working on the schematic, but having many people working on the same board is very challenging. If you have any things to add to an open source hardware project, how would you do it? Make changes in your own fork? Or tell the devs about your idea
Looking for insights on how to make a community open-source hardware project.

@hemalchevli.bsky.social · last yr.

Which interface to route first?
Here is the list of priorities of interfaces to route when laying out PCB.

Its recommended to start with the high speed and make your way to low speed. This way when you are staring out there is a lot of open space for these interfaces. These will have less issues due to less discontinuities. The low speed can be routed around the high speed ones with lots of layer changes and vias.

PCI Express
USB 3.0
SATA
Ethernet
HDMI
LVDS
USB 2.0
SD/MMC/SDIO
Parallel RGB LCD
Parallel Camera
Digital Audio
VGA
Analog audio, DC
Low speed interfaces (I2C, UART, SPI, CAN, S/PDIF, and GPIO)

This give clarity on how to start on any big PCB with multiple interfaces.

@hemalchevli.bsky.social · last yr.

45 vs 90 degree trace - here we go again

This discussion pops up from time to time.

Here is the TLDR. For low speed signals, it really doesn’t matter what you use. For high speed 45 angled traces are better than 90, but arcs are the best.

There is strong opposition to using 90 degree traces, arguments like acid traps really don't apply to newer manufacturing techniques. If you are designing anything low speed, you can use any angle trace and you will be fine.

When using high speed, 90 degree traces should be avoided, not because of the manufacturing reasons or that the electrons fall off at the bends. But because it poses an impedance discontinuity. For high speed, if the EDA allows, its best to use arcs, next best case is 45 degree trace.

Hope this helps you draw your traces at the correct angle.

@hemalchevli.bsky.social · last yr.

Requirements and Specifications - Know the difference.

To build a successful product you must have a clear idea of what to build and how to plan for it.

It all starts with writing down the requirements and specifications. Requirements and specifications, often used interchangeably, are very different. Requirement is what the product is expected to do. Specifications are how the product is going to achieve it.

When designing a product, if you are lucky you will be given both to start the design. More often than not, you have to come up with both of them.

Other than that, requirements should be implementation free. It should just state what is required without identifying the how. It should be atomic, meaning each line must have only one requirement. Make sure there are no duplicates, one might use different terminologies to express the same thing.

The keen ones jump to selecting components right at the requirements phase. And worse yet selecting the same component for all the projects. This is not good engineering practice.

Don't stop at building projects, go further, make products.

@hemalchevli.bsky.social · last yr.

Why doesn't characteristic impedance depend on track length? 🧵

@hemalchevli.bsky.social · last yr.

Check out these 7 Electronics podcasts for honing your skills

Here is a list of electronics and embedded related podcasts. I love listening to these. Its a great way of keeping yourself up to date with the evolving tech. Sometimes apart from the technical learning they have amazing stories that are very interesting and entertaining. I’m not affiliated with any of them, I find them of good value.

Amphour - I’m sure most of the people in the industry have heard of them. It's a mix of technical discussions, interviews with leaders in their field. I’ve learned a lot from this podcast.
Embedded.fm - With the ASMR voice of Elecia, this podcast talks more about the software side and is filled with a lot of insights.
OnTrack - This one is from Altium and they have very good interviews with industry leaders, there is always a plug from Altium but that alright for the value it provides.
Unnamed reverse engineering - This is a hidden gem. I really like the vibe of the both hosts and I’m left with a lot of positivity after the podcasts. They talk about reverse engineering and security.
Circuit Break: A MacroFab Podcast - It's a great podcast to learn things about manufacturing and design challenges.
Hackaday Podcast - Hosted by hackaday writers, it's a great way to learn about latest projects and hacks.
The EEcosystem Podcast - Hosted by Judy Warner, who was a previous host of the OnTrack podcast from Altium. This podcast has really experienced guests and is packed with a lot of wisdom.

Let me know if there are any hidden gems to add to the list!

@hemalchevli.bsky.social · last yr.

How much silkscreen is enough?

When you design a PCB, in most EDA tools the designators (R1,C4 U7, etc.) are placed on the silkscreen.

Silkscreen layer is for information not data. Sometimes we are so involved with the layout we forget about the silkscreen. On the PCB say you have LEDs, and its called D1,D2,D3 etc. And this makes it to the silkscreen.

These are of no use to the user.

Instead, if you write the purpose of the LED for example, PWR or STATUS or ERROR. Then the user immediately knows what the LED on means. Not everyone will have access to the schematic, and for people using the board on the field, even if they have access to the schematic, they are not going to find where D1 is located and what it does.

The same thing goes for switches, instead of SW1, write the purpose of the switch, is it a reboot switch or power switch.

@hemalchevli.bsky.social · last yr.

Calculate this before Length matching Differential pair

When moving up from low speed design to high speed design, I saw engineers trying to length match USB 2.0 within 0.1mm or even closer to zero.

Yes, zero skew is the best but sometimes due to some reason, the EDA tool might not be able to remove the skew between the differential pair. Let's take an example of USB 2.0. There is a max allowable skew, typically cited as 7.5 picoseconds for onboard skew, there is a higher skew.

So we should try to minimize it as much as we can to reserve the budget for the cable, so as not to have the product work with some particular USB cable, it should work with all quality of cables.

Let's translate this 7.5 ps to the difference in the trace length. Assume Er of 4 and we are routing differential micro strip lines. This translates to 1.12mm of allowable skew for USB 2.0. Now when you route your signal, check what's the maximum allowed skew and what length it translates to.

Add this length into the rule of the EDA tool so you know when you are within the limit.

@hemalchevli.bsky.social · last yr.

Beware of Inrush Current: Why More Capacitors Aren't Always Better
When you design a product and if you are not really sure if you need an extra capacitor for one of the IC or a module. You add it for extra measure and maybe it's also recommended by the app note or the reference design.

It's not common to see issues arising from adding extra caps to the board, it is generally regarded as not a problem. The argument goes like this, its better to have and not need than to need and not have the capacitors. The issue that is overlooked is the problem of inrush current.

This problem occurs only when you turn on the device. For a short amount of time when the capacitors are charging the power supply can see it as a short for a brief period of time. Imagine what happens to the traces on the board.

You designed the board traces with load requirements you had and now due to inrush currents, they might be carrying more current than intended.

This leads to heating of the trace and some products can fail after some use. It could be very hard to detect the cause, as this issue is hard to detect. Especially if you don't know where to look.

Sometimes, less is indeed more.

@hemalchevli.bsky.social · last yr.

Today, I want to talk about two ICs with the same footprint and the same function, yet they may not work interchangeably.
The ICs in this discussion are the hex buffer, CD4050B and 74HC04. To someone starting in electronics, these may look the same in terms of the function, physical footprint and pinout. One might assume these can be interchanged. Well, not quite.
Since they belong to different families, there is an electrical difference within the IC.
The older CD4000 series can have around 5 to 10 times longer rise times. And from the previous post about TEL, the length of the trace where the signal integrity issues start is different for each. So if you drop in the new 74HC04 buffer in a design with long traces, the system will have issues.
When you find a Pin-compatible replacement for your IC for one the components, check out the rise times.

@hemalchevli.bsky.social · last yr.

@hemalchevli.bsky.social · last yr.

@hemalchevli.bsky.social · last yr.

Save this Reference designs list Here are 9 reference designs that can help you in becoming a better PCB designer. None of the below are any affiliations, these are the boards I’ve collected over a course of time. 🧵

@hemalchevli.bsky.social · last yr.

8 ways to make your schematic more readable 🧵

@hemalchevli.bsky.social · last yr.