Hot answers tagged

65

Don't look to the arduino designs as examples of stellar electrical engineering. However, there can be a legitimate case for doing this. This part contains 4 resistors. If it was already there for another reason, especially if several more of them are used on the same board, then using two of the resistors that would otherwise go unused in parallel to ...


45

I assume that you are using the autorouter because you think it will save your time. But I have some bad news: it is said that PCB layout is 80% component placement, 20% routing. You can't just slap down components, you need to think about how the signals connect and if you place the components right, the layout will "flow" from this placement. So if you ...


23

Before computers were cheap and available enough to be used for such things, a "layout person" (a specialty of draftsman) would manually design the board layout. This was done on a drafting table at larger size than the real board. The engineer provided a D-size schematic to generate the board from. The layout guy would lightly pencil in tracks, then use ...


22

There are quite a number of things that will do this to you. You have not stated the length of the interface. I do direct chip to chip PCIe frequently and you really need to take this into account as you will get attenuation of roughly 0.18dB per inch due to skin effect losses and about 0.5dB per inch due to dielectric absorption on 'ordinary' FR4. I think ...


22

Unlike what others have said, using the auto-router isn't the problem. They are right in that you can't just throw a whole design at the auto-router and expect it to solve everything for you. But, when used properly, auto-routers are legitimate and time-saving tools. Don't listen to the knee-jerkers that say not to use the auto-router. Your problem is ...


22

It is most likely Fritzing. It is an educational free software quite popular among newbies and teachers. It can draw wiring diagrams like the one you posted, or true schematics and even PCB layouts. It can't simulate the circuit, though. As Felthry and JRE said in comments, using Fritzing is frowned upon on this site and by professional engineers because ...


22

Simple answer is you don't split planes unless you know what you are doing and why you are doing it. Separate the ground planes and route signals over the the gap in a split ground planes at your own peril. The lowest inductance path for return currents is on the ground plane directly under the signal trace. This forms the smallest possible 3D loop. But the ...


20

First off, use a 4 layer board. Not only does it make layout easier but inner ground and power planes provides a barrier against front/back crosstalk. Also, 4 layer is not much more expensive than 2 layer Second, lines crossing is nowhere near as bad as lines running parallel


20

The auto-router isn't magic. And shouldn't be used to do full boards. You first need to route the important bits yourself. Like power, high speed and bypass caps. Then you can let the auto-route do the tedious stuff. Design rules must be setup flawless for the auto-router to work correctly. Now it looks like you've randomly placed the components. You get ...


19

Lower track impedance In a switching regulator, the track impedance matters a lot. Not only resistance, but also inductance, and both are reduced when using wider tracks (or planes). Heatsinking A switching regulator produces heat, which has to be channeled out of the component. Copper is a very good heat conductor and is used as radiator in many switched ...


18

The hole for the connector would be near the center of the MCU package, away from the pins. This is a very bad idea. Usually the pins from through-hole parts stick through the board by at least a millimeter, more than enough to interfere with the ability to place a chip where it would cover the pin. You could conceivably cut the pin short enough that it ...


17

Actually, if you look closely you see that many of these holes connect switch channels with their common signal (ground or supply). So this is simply to test the fabrication of the FPC itself, before it is put through the expensive process of trying to put relatively large switches onto a flexible substrate. Happens quite often that an FPC features special ...


17

Adding to Dirk's Answer Be aware, mounting on both sides of a board may not buy you as much real estate as you might be imagining. When it comes to board density, your ability to route traces tends to be a critical factor as density goes up. More layers helps, but then you fill up space with vias. Double sided tends to make it MUCH harder to route unless ...


16

Your suggestions are spot on. Solder your components first, but think about what you could use as a wire, e.g. a resistor can be used as a jumper. ICs are the main thing to put in first, as they are set and will have a lot of dense connections. Try and work in a matrix, with all wires/components running along rows and columns. Rails are best - you'll have ...


15

The best advice I can give you is keep heavy stuff along the centreline. This also applies to xtal oscillators you may be using. You might also want to ensure that the mass of elements you use are balanced about the centreline of spin or you might get some heavy-duty vibration. For small/low mass SMT components surface mount is fine but it might be worth ...


14

For the same reasons as Olin mentioned, using two distinctly seperate resistors in parallel can be a saving if those resistors are used elsewhere on the PCB. Line items in the build need to be stocked and counted and there is a real annual cost for this.


14

There's a great book from Henry Ott that covers this -- unfortunately I'm on vacation so I can't take a picture of the relevant diagram. The book is Electromagnetic Compatibility Engineering. Here's some quick points though: from a DC power point of view, how much current does your device require? Look at the rating of each conductor, de-rate if necessary ...


14

For FR4, using effective epsilon of 3.25 we get the wavelength of a 80 MHz signal in the PCB at 80 by calculating wavelength = (c/f) * (1/sqrt(epsilon)) = (300000000 m/s / 80000000 1/s) * (1/sqrt(3.25) = 2.06 meters. Using 1/16 of wavelength as the "safe limit" below which we don't need to worry about reflections and relative signal timing, it's ...


14

Even though you are using perf-board to build your projects, there is nothing stopping you from using schematic capture and PCB layout software to lay out the placement of your components. Doing this would benefit you in several ways: You would learn a useful skill doing this. The software can generate and check your netlist to verify you've actually ...


14

You have made one of the biggest mistakes a newbie can make, and that is trust the autorouter to do your work for you. This is a huge misunderstanding among hobbyists, and that is that the autorouter is for beginners. In reality it is the exact opposite. Only expert Altium (and other package) users can properly use it, and by the time they become experts it ...


13

So you could fill a book with the answer to this question, in fact I think I have some on my shelf Let’s run through your questions. Should you use a 4 layer board instead of a 2 layer? I say absolutely yes, the cost argument to going 2 layer is a weak one at best compared to the advantages. Obviously it can be done, and is done, and in this devices ...


13

That comes from running a design rule check with no traces routed. It is showing you the rubber band connections that are not complete. Go to Tools->Reset Error Markers to get rid of them. The rubber band lines will stay but the 'capacitor' error markers will go away.


12

A schematic is not meant to be a drawing of a circuit, and shouldn't be used that way. The "pins" in a schematic just show connections. Put them wherever they need to go to make the drawing understandable, and don't worry about what they convey physically.


12

Try pressing B. That will re-draw all fill zones on the board.


11

If you are making your own boards, then you want traces as large as you can get by with -- perhaps 15 mils (0.015") for signal traces, and 30 mils for power. Note: with traces that large, you will typically have to narrow the traces down a bit before connecting to IC's pins with fine pitch pads. If you are having a board house make your boards, then you ...


11

What you're looking at is a PC expansion board using the ISA expansion bus. This uses the then-standard .100 inch contact spacing which was widely available. There are a number of reasons for this. First, the connectors were cheap and fairly reliable. Second, when the PC was introduced, DIP package ICs were the norm, rather than surface mount. This means ...


11

This rule aims to solve a manufacturing problem known as tombstone. During reflow, a too large connection to an SMD pad acts like a heatsink, creating a situation where one side of the component has a slightly lower temperature. Because of this, one side of the component can lift up from the PCB. This is especially true for small (0402 and smaller) ...


11

You are getting confused about the impedance. The type of CAN you are apparently using is implemented as twisted pair with roughly 120 Ω impedance. That is why there is a 120 Ω resistor on each end. That means the bus looks like 60 Ω to a driver, but the transmission line itself is still 120 Ω. Since drivers drive in the middle of ...


11

You should be able to figure out it looking at the device as whole. You can find such numbering in the devices with multiple boards, multiple physical or logical blocks in it. First digit may designate block #, other two (usually) designate component # in the block.


11

Heat and low impedance for the high current paths. Some of the land area on this board might be non-critical but when you have the empty board space it provides a little extra safety margin. It is generally not a good idea to create a large land area for the switching node (probably on the lower right of this image, but hard to tell without part numbers/...


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