Timeline for SPI cable with twisted pairs with ground: Are ground loops an issue?
Current License: CC BY-SA 4.0
16 events
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| May 20 at 12:35 | comment | added | Tommy95 | I wish I could go lower, Lundin, but at the moment I have a recurring timer interrupt routine occurring every 2 ms, which lasts 1 ms. I take sensor measurements every 2 seconds, so I have 2000 slots of 1ms processor time to collect sensor data but via spi I don’t know how to divide the task over these 2000 slots. Would you please have some insights on this? | |
| May 20 at 10:02 | comment | added | Lundin | Out of curiousity, why do you need 10MHz? What manner of application is it? | |
| May 19 at 22:18 | vote | accept | Tommy95 | ||
| May 19 at 18:13 | history | edited | Tim Williams | CC BY-SA 4.0 |
Added info from comments
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| May 19 at 18:11 | comment | added | Tim Williams | Well, a "hard find" wouldn't be generic..! | |
| May 19 at 18:11 | comment | added | Tommy95 | Yes! 5 twisted pairs, a hard find to be honest | |
| May 19 at 18:11 | comment | added | Tim Williams | Ah, D-sub. Is this generic multiconductor cable then? | |
| May 19 at 18:10 | comment | added | Tommy95 | Aluminium foil + metal braid connected to chassis ground on both sides via D-SUB connectors. Chassis ground isn't connected to signal ground on sensor side, only on master side. | |
| May 19 at 18:09 | comment | added | Tim Williams |
@st2000 FYI -- in fact, USB is a poor example: the SE0 bus state is a common-mode signal. I think a lot of people forget this, and hand-wave that USB is differential, and then lift their shield grounds, and wailing and gnashing of teeth ensues. As for twisting with a signal, consider the limiting case, a signal surrounded by ground wires: you'd have coax. There's certainly nothing wrong with a signal going through a good old coax cable!
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| May 19 at 18:00 | comment | added | Tim Williams | What kind of "shielding" are we talking? | |
| May 19 at 16:35 | answer | added | TQQQ | timeline score: 0 | |
| May 19 at 16:08 | history | edited | Tommy95 | CC BY-SA 4.0 |
added 35 characters in body
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| May 19 at 15:57 | comment | added | Justme | @st2000 Twisting a signle-ended signal with ground means it has well defined characteristic impedance. Yes OP has been warned about 10 MHz logic level not being the best way to do it, but with proper design it might just work for 1 meter with these buffers. And I2C is successfully used for interfaces like VGA, DVI and HDMI for tens of meters so it can also work if properly designed. | |
| May 19 at 15:55 | comment | added | st2000 | Just a guess, so I'm adding a comment, not an answer. I thought one twisted balanced pair signals. Such as the Data+ and Data- of a USB cable. In this way, common noise can be canceled out at the receiver. I don't think there is much if anything to be gained by twisting ground and a signal that changes with respect to that ground. Also, I am sure SPI, I2C and other such chip to chip signals are only designed to travel short distances. As on a circuit board. That said, I have seen them used over longer distances. But special circuits are commonly employed. Still, they are not the best choice. | |
| May 19 at 15:54 | answer | added | Justme | timeline score: 3 | |
| May 19 at 15:36 | history | asked | Tommy95 | CC BY-SA 4.0 |