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 ...


20

Assuming you're only using USB-low-speed or full-speed, you should be fine. Generally, layout considerations only really have to be taken if you're going long distances (many inches), or using USB-2.0. Even then, USB is surprisingly tolerant. USB 1.1 or USB2.0 low/full speed You really don't need to worry. There are (possibly apocraphyal) stories of ...


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 ...


20

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 ...


20

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 ...


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 ...


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 ...


16

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 ...


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 any serious work, you won't want to get parts made by someone else because they won't adhere to your conventions. I always make my own parts, which is really not that difficult. I have certain requirements for parts, like attributes for automatic BOM generation, and text at particular sizes and and layers for the silkscreen, the assembly drawing, etc. ...


14

(1) Finding existing Eagle parts already created by other people out there: I recommend the following four sources ( aside from Googling "partname Eagle" ;-) ): You can look in Cadsoft's searchable collection of Eagle libraries You can use Jason Tribbeck's Eagle part/package/device search, which allows wildcard/partial-term searches You can use Esawdust's ...


14

There isn't one. That said, there are some thing I've gathered over time. What you do with the ground planes depends heavily on what you're trying to do. You could be trying to provide low impedance paths, or you could be trying to isolate one area from another, or you could be trying to deal with EMI. There certainly is a performance penalty for doing ...


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

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

You'll always have some noise on an ADC, especially SA (Successive Approximation) types on the microcontroller die. Sigma-delta perform better for Gaussian noise, as they integrate it. Don't expect 12 ENOB from a 12-bit ADC. The controller's noise is a reason why most microcontrollers don't give you a higher resolution than 10 bit, and the AVR offers the ...


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.


13

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 ...


12

You will never find an absolutely complete parts library from any vendor. What you need to do is learn how to use the library editor of your tool. There you create packages and symbols that you can place in your schematic and layout, based on the datasheets from the manufacturer. As far as simulation goes, there is no complete/unified tool for this. You'...


12

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 ...


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.


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