# Tag Info

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NoOOoooOOoOoooo. That's such a waste of a 4-layer PCB! Please find another approach than shorting two adjacent planes together to turn a very useful 4-layer PCB into effectively what is a 3-layer PCB. That aside, there is also called a method called via fencing. It is like a ground ring, except in 3 dimensions where you tie parallel ground traces on layers ...

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Why waste both middle layers for a ground plane? If you have ground traces on the board, especially lateral ones for shielding, they should be nailed to the ground plane at least every $\lambda/20$. If that's a square wave clock, the harmonics will go way above 10 MHz.

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Some jackass installed a grounded receptacle so they would have the convenience of being able to plug in things which require grounds. However they did not actually hook up the grounds. That's why they ring out to nothin', as SimonB says. The small voltages you are seeing are because you are using a DVM (most cheapie DVMs are very high impedance, which ...

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@VE7JRO provides a great illustration and explains the aircraft procedure, but doesn't explain the magneto. Which we should do here on EE. The magnetic field passing across the coil is not moving fast enough to create a high voltage spark. The spark is produced by having the points open in the middle of the cycle, after the coil has been charged. With ...

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So on lawnmowers the magnetos have two coils. One of them is high tension with very fine wire and a huge number of turns, the large number is required for high enough voltage to ionize air and cause a spark, which ends up being a tiny current due to high coil resistance and inductance. The spark pulse is cause by induced voltage pulse caused by a field pulse ...

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There is an excellent Q+A with a nice image of the ignition system here: aircraft high-tension magneto ignition system. There are a couple of things a pilot can do to ensure the aircraft engine will not start if the prop is spun by hand. Let's assume we are talking about a Cessna product with a carburetor. Live mag check. Before shutting down the engine, ...

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"P-lead" is not an electrical engineering term. It appears to be exclusively a term used with aircraft magnetos. In electrical engineering, we would call the "p-lead" connection a short circuit. It provides a low resistance path that allows current to flow past an area where you want to prevent it from flowing. For an engine with a magneto connecting the "P-...

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I was taught, by a guy from Bell Labs, that coax cables are not really effective until about 100,000 Hz. And even then, some of the energy will still venture outside the coax ---- because the energy uses ALL paths back home, and a bit of energy 80db down yet outside the coax ---is still allowed by mother nature.

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There is no sharp cutoff for DC and switching signals as to how closely the return currents follow the signal; at DC the return path will indeed spread out and for switching signals, as the edge rate gets faster, the return path will follow the signal track more closely. The return path will take the path requiring the least energy in my experience so even ...

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You could do that, but it's not generally done because the higher the frequency, the less of an issue EMC is. Frequencies that cause EMC issues are generally high enough that the return path follows the red line. Unless you have some extreme EMC requirements at frequencies below about 10MHz, or sensitive magnetic instruments nearby, it's not usually ...

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Your question is slightly unclear, but I will answer what I can. If you want to prevent your signal trace from acting as an antenna, you could use the trick of parallel lines of exactly equal length and thickness, but you would have to use differential signalling instead of the ground-referenced one. You can see how that is done on computer mainboards for ...

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A 'centre-tapped' secondary is actually two identical secondary windings connected in series, as shown. The dots indicate identical winding ends (current direction being outward at the dotted ends and inward at the opposite ends at the same instant of time or vice versa). With the windings so connected (series-aiding), the total voltage would be 240 V. ...

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Relative to G, at a particular instant in time, A will have a peak voltage of 170V and, also relative to G, B will have a peak voltage of -170V. Assuming the line frequency is 50Hz then 10ms later A will be at -170V peak and B will be at +170V peak, both voltages being relative to G.

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With DC it's obvious. simulate this circuit – Schematic created using CircuitLab Figure 1. Two 9 V batteries series connected but with various grounding options. How can B be at a 120V less than G, what would that mean? Can someone explain the theory behind why/how this works? You are forgetting that your meter only measures magnitude of an AC ...

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Try not to think about the voltage potentials in relation to the vertical direction of your diagram. Also, transformers work on AC, not DC, so the actual voltages are constantly changing with respect to each other in time. 0V is a relative term in AC. In fact, at 60Hz, A and G alternate being 0V 60 times a second. But it's convenient to think of the ...

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At some instant in time, "A" will be at +120 V relative to the center tap, and "B" will be at -120 Volts relative to the center tap. A half-cycle later, "A" will be -120 V, and "B" will be +120 V. The voltages on A and B relative to G will be continually changing, but they will always be the same magnitude, but opposite polarity.

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The outputs are anti-phase. When other phase has maximum, the other phase has minimum. If you were able to measure the phase, the other would be +120VAC and the other one -120VAC, but the polarity/phase is not indicated with minus sign, but with degrees of phase. Same as with two 9V batteries, it's 18V between ends, 9V over one battery and 0V center, and -9V ...

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It was a mistake. By connecting the dongle GND to the common GND on my board, instead of output B, not only the strong noise completely disapeared (meaning something there was conflicting tension between A and B) but an indicator led on the dongle stopped shining. Because they sell these things without any serious instruction, I didn't know this LED means ...

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Figure 1. R3 and R21's ground points in what appears to be an audio pre-amplifier. ... but if I decide to let the signal go to ground in another point as shown in the schematic, would it affect the signal? A schematic is not a physical wiring or layout diagram. It is supposed to show the schema or function and connections of the various componenents. All ...

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Depends what kind of circuits and return currents you have, but knowing how to ground is important and that is why concepts like star ground or ground plane exist. Obviously long wires with large currents are worse that short wires with large currents, and for example when building an audio amplifier, you dont't want the power amp ground path current cause ...

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The +12V and -12V are used to power the audio sections of the keyboard. If you measure the voltage between +12V and -12V, you will find 24V total. AG is the audio ground. If you measure from +12V (red lead to +) to AG, then you will find 12V. If you measure from -12V (red lead to -) to AG, then you will find -12V. This known as a "dual rail power ...

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Let's get one thing absolutely clear: split/partitioned ground planes are never necessary, but they can be a useful technique to mitigate human error. But you can always achieve equal or slightly better performance using a single, unpartitioned or slotted ground plane and careful routing of your board. However, most mixed signal routing is also fairly ...

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Something I learned years ago (decades?) from a couple of great FAE's from Unitrode: "the chainsaw rule". Basically you have the major ground cuts correct, but you must follow the rule that you need to be able to cut the fiberglass with a chainsaw right thru the ground cuts that you have made. I.e., don't put any traces or copper pours over those cuts. ...

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I saw in some cases a common ground wire is needed to prevent common mode voltages to saturate the amplifier; but how come a multi-meter does not suffer from the same issue? A multimeter is battery powered and therefore extensively galvanically isolated from true ground. Multi-meter can be floating but CM voltages can pass through air via ...

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You could consider: RS-485 drivers in between (full-duplex, or half-duplex if your debug protocols support it) Opto-isolators near the converter

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Instead of adding junk on the output of your buffer, just use an AND gate instead. For example, 74LVC1G08 or 74LVC2G08, which have the same 32 mA output drive capability as the 74LVC2G125 you're using now. If you need the Schmitt trigger feature on the input, and the negative enable logic, you can combine a Schmitt trigger inverter and a NOR gate: ...

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The problem may not be that the metal box has a voltage potential with respect to ground It may be that you have picked up a static charge (from the air, petting the cat, or rubbing your shoes on the carpet, etc.). If so, the best bet is to discharge yourself first, by slapping a nearby metal water faucet, etc. or other grounded appliance, before touching ...

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i have an idea to connect metal box to ground using following circuit but i dont know if it would work or what part numbers should i use. In my theory when the voltage rises more than 5v the zener diode should pass the current then resistor should convert electricity to heat. Your circuit is fine, but the diode isn't required. Just use a resistor to ground. ...

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Lets suppose the power transformer has primary-secondary overlap area of 10cm * 10cm, and insulation thickness (between those windings) of 1mm. Assume the Er (relative permittivity) is 5. What is the capacitance? C= E0 * Er * Area/distance C = 9e-12 farad/meter * 5 * (0.1 meter * 0.1meter) / 0.001 meter C = 45e-12 * 10 = 450 pF = 0.45 nanoFarad What is ...

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The potential difference comes from capacitive coupling between mains voltage side and low voltage side inside the ungrounded power supply. Sometimes you can even feel it by touching only the 9VDC output, and the effect can be amplified if you touch scope ground at the same time. It kind of stings if the contact area to skin is small. It is either due to ...

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The correct answer is in the comments, but a future reader may find it hard to follow. Just to make it clear: If you add an isolation transformer:

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It seems that the control box can only power low current devices. So this is why using a relay can be helpful. To activate the relay, the pin 85 is connected to the "controller box wire" and pin 86 is connected to 12v power supply. So when the remote control is activated and in turn the control box wire is "activated" and the relay's coil is powered using a ...

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Insert a optocoupler. Connect the LED of the optocoupler (if necessary, with a resistor) between the 12V and "output wire of control box" and the transistor of the optocoupler to the "wire to control this door opener" and ground. My phone does not support the built in schematic editor. Below an attempt to draw the implementation:

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