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51

If you just ignore the POE 48 Volts in the image below, you can see Ethernet uses transformers on both sides. This way there is no need for common ground as long as the common mode voltage stays below 1500V generally. The isolation specification of the transformers. And as a bonus you now also know how POE works. (802.3at) However, CAT6A often has a ...


29

Why is Ethernet not grounded? There are two reasons: 1. It would create a ground loop between devices 2. The device would also be more susceptible to ESD which is prevalent in cables that are being moved or handled (from triboelectric charging of the cable) The reason Ethernet is more susceptible to a ground loop is because: The loops could be much ...


28

One very good reason, as I learned myself from a recent prototype, is reversing the physical layout of the IC in a circuit. I plugged a through-hole version of this microcontroller into a socket backwards, and spent about an hour with an oscilloscope trying to determine why pins were not behaving as expected. When I discovered the IC was in backwards (and ...


19

The CAN pins do not have fixed pin assignments. Instead you are able to select which of the "Remappable Pins" you wish to use (RP0 through RP15). If you refer to page 180 of the datasheet, specifically the table titled "REGISTER 11-16" (RPINR26: Peripheral Pin Select Input Register 26), it details the register used to select the CAN RX pin location (C1RXR). ...


18

I've recently rolled my own as far as I2C connectors go. The connector itself is not very important, right now I'm just using 100mil pitch header (usually female on board so it's not so pokey when not connected), but any 4plus pin connector will do. Additionally, I'm using the P82B715 from TI as an I2C bus extender. This overcomes the capacitance issues ...


17

Differential signaling means that there is no need for a common ground as a reference point. Also, negates the need for shielding, which is usually grounded. No DC power transfer again removes the need for a common ground and makes point #3 possible. Galvanic separation makes grounding counterproductive. Specs put considerable effort into making devices at ...


16

The loops represent a shield around cable that then connects to the connector pin indicated by the line from the loop. In your example there is a two wire pair that is shielded and then that is contained with some other wires and an overall outer shield.


16

They indicate data direction. Arrows pointing to the chip indicate that those pins are inputs and vice versa. Bidirectional arrows indicate they are either inputs/outputs, depending on the circumstances. If you want to memorize it, I think you should memorize those pins meanings first.


14

Normally the square pad is pin 1. The left picture looks like a DE9 connector - on that connector family, the pins are numbered along the row from pin 1, then the second row is numbered in the same direction, like: 5 4 3 2 1 9 8 7 6 For the rectangular array in your second picture, pins may be numbered either row by row, or column by column, ...


14

The 80QFP is thin enough that you may be able to place it upside down on the board, glue it in place, then carefully bend each pin down to its corresponding pad, and solder it. 80 pins is a lot to do that for though, this method is more commonly used on smaller chips. I'm trying to find a good picture showing this technique. At least, that's what I would ...


13

As you say, it is a complete non-issue for high-volume manufacturing, which is where the vast bulk of such chips goes — and those are the customers that the chip makers pay attention to. Hobbyists don't buy nearly enough chips for them to even notice. But yes, there are real advantages to this arrangement, both on the chip and on the board. Power and ...


12

I don't know the exact reasoning for JTAG, but when high speed signals are used and according to the best practices, you should put a GND in between every signal of a flat cable. JTAG can be considered as a High Speed Signal. Multiple GND wires are used to avoid crosstalk between the signal lines. They avoid capacitive coupling between adjacent lines. And ...


12

Grounding is often misunderstood to be the end-all solution for connecting things together. However, in most cases, even on short runs, grounding adds more issues than it solves. The issue with sharing a ground over any distance is you are assuming both ends are at the same ground potential. In a perfect world that may be true, but in real life it almost ...


11

When it was first established, the I2C (Inter-Integrated Circuit) bus was only intended to connect chips on a single PCB assembly. It was never intended to be used on cables to connect multiple boards together, and therefore, no connectors for that purpose were defined. The only "standard" I2C-based external interfaces I'm aware of are the short-lived ...


11

Historically, it was more efficient to put multiple instances of the same function into the same chip, so DIP packages usually had at least 14 pins. The JEDEC MS-015 standard never had defined packages smaller than eight pins: (Note that 10-, 12-, and 26-pin packages are also missing.) With nobody actually manufacturing six-pin packages, the first one to ...


11

The default in logic circuits is that a high level (logic one) activates a function. The small circle denotes inversion, so we can have an external signal that is active low, which (when low) activates a function (that is still activated by the more-or-less theoretical signal after the circle, which is active high). The fact that a signal is active low can ...


10

There are two common projection methods for technical drawings. First-angle projection First-angle projection is as if the object were sitting on the paper and, from the "face" (front) view, it is rolled to the right to show the left side or rolled up to show its bottom. Third-angle projection Third-angle is as if the object were a box to be unfolded. If ...


10

The schematic of a typical coaxial (barrel type) power jack looks like this: In that schematic view the pin numbers correspond as follows: Pin 1 - SLEEVE TERMINAL Pin 2 - SHUNT TERMINAL Pin 3 - TIP TERMINAL Looking at the power supply cable end the terminals in correspondence are: The SHUNT terminal serves as a switch terminal that opens (for most ...


10

It's a complex topic that only the manufacturer can fully answer. There's lots of decisions when it comes to pin bonding, but in short, it's about EMC, internal supplies and internal clocks. The sensitive pins are those for supply, ground, oscillator/PLL and ADC. The GPIO pins around probably the least sensitive ones, so where they end up is the less ...


10

The LM385 was originally produced by National Semiconductor. The earliest reference I can find is from their 1980 Linear Databook. It shows the same 'wrong' pinout. Other manufacturers whose datasheets have the same pinout include Motorola and Telcom Semiconductor. So it seems the 'wrong' pinout originated at National Semiconductor, and has been copied by ...


10

One edge of the package is beveled. Pin 1 is on the beveled side.


9

CE (chip enable) may also be named CS (chip select), as it is in the timing diagrams below. The others are WE (write enable) and OE (output enable). These are all active low (indicated by the overbar), but since that can't be done with ASCII characters I will use a # suffix in the text below, e.g. CS#. CE#/CS# is normally high. To read the RAM, the ...


9

This is a comment - converted to an answer. If there is still some doubt in your mind, use a continuity tester to make sure all the grounds are connected, since these will likely have unique locations you should be able to verify which of the pins are connected together. For example pins 27,28 and 49,50 are a unique grouping that doesn't occur on other ...


9

I have designed a board for the STM32F103R, like you. Tested and "proven" now. Anyway, if the text is right-side-up, pin 1 is in the lower left. The other answers all mention things that could be considered a "hint", Luckily those hints all point in the same direction and happen to be correct.


9

Single OpAmps come in 5 and 6 pin packages these days. You just won't find them in DIP anymore because most of the industry has moved to SMD packages. It's easier and cheaper to work with them if you're into mass production. For example 5 pin single OpAmps often come in the SOT23-5 package which looks like this: There are 6 pin variants as well. These ...


9

Neither of your circuits is correct. The correct circuit looks like this: simulate this circuit – Schematic created using CircuitLab If you connect it incorrectly (as in the first circuit) it may act as a zener, resistor, zener + resistor, etc. and give you some voltage drop or whatever. I doubt you tested the I-V characteristics thoroughly over a ...


8

Latex + TikZ is popular in academia and you can use it to programmatically create very clean diagrams. Illustrator is more user friendly, mass-marketed and has a more shallow learning curves. Inkscape is open source software similar to Illustrator. Visio is a diagram tool produced by Microsoft. Widely used in engineering departments.


8

It's only to make the relay cheap. It's sub-optimal internally (electrically) as well as externally (pinout). The coil-to-contact breakdown voltage and capacitance is inferior to that of better relays. On the other hand it's cheap and the relay can be made reasonably sensitive (360mW typically for that construction). One of the disadvantages of this ...


8

This is a common issue when interconnecting boards with ribbon cables if you do not think it through properly. There is no real resource for this, other than anecdotal answers like this one. Your proper method is to have the actual parts in hand when you are designing your system and see/understand how things are going to fit together and what that requires ...


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