Timeline for transmitting 5v signal over a long cable
Current License: CC BY-SA 3.0
16 events
| when toggle format | what | by | license | comment | |
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| Jan 20, 2013 at 16:38 | comment | added | The Photon | @ChrisStratton, That is true. That does not mean it is not a real situation. | |
| Jan 20, 2013 at 16:36 | comment | added | Chris Stratton | "Ground loop" is a term that gets misused 100 times by someone with no idea what they are talking about, for every time it is used meaningfully and legitimately. | |
| Jan 20, 2013 at 16:33 | comment | added | The Photon | @ChrisStratton, those are good examples of situations where ground loops are likely to cause problems. | |
| Jan 20, 2013 at 15:47 | comment | added | Chris Stratton | In practice optoisolated interfaces tend to be reserved for situations where there's an expectation of an unusual risk of problems - industrial environments which large switching currents nearby, stage settings with lots of power and poor wiring (midi), etc. For most applications, it's really neither necessary nor common. | |
| Jan 20, 2013 at 5:39 | comment | added | The Photon | @ChrisStratton, ExcitingProjects, it's not a matter of what's simpler or more complex, it's what kind of transients are you trying to protect against, common-mode or differential. I had to sleep on this one before I saw it, but see my edit for more details. | |
| Jan 20, 2013 at 5:35 | history | edited | The Photon | CC BY-SA 3.0 |
common-mode vs differential transients
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| Jan 20, 2013 at 5:22 | comment | added | ExcitingProjects | @ChrisStratton "Simple" does not mean better, it only means simple. Try and understand the combination of solutions that ThePhoton says, rather than jumping to conclusions. | |
| Jan 17, 2013 at 17:14 | comment | added | The Photon | @ChrisStratton I think if I was using the optocoupler, I would add something close to this circuit in front to prevent transients blowing out the optocoupler. | |
| Jan 17, 2013 at 17:08 | comment | added | Chris Stratton | This is the better answer. It's simple, and the resistor at the receiving end will help absorb reflections, though better performance might be had if the resistor were moved to the sending end. | |
| Jan 17, 2013 at 16:07 | comment | added | The Photon | @CodenamedSC, This circuit is functionally equivalent to the 7805 idea. The main drawback of the 7805 is, the 7805 doesn't have any capability to absorb the transients that might be generated by interference on the cable. Either this circuit or the optocoupler circuit should be able to handle brief transients in the 100's of volts, which the 7805 is not designed for. | |
| Jan 17, 2013 at 16:04 | history | edited | The Photon | CC BY-SA 3.0 |
add improved circuit
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| Jan 17, 2013 at 14:08 | comment | added | John U | @CodenamedSC - I can't really explain this large gap in your electrical knowledge/understanding here, I don't really have enough time, but please trust me the 7805 is a really poor way of doing this - both of the suggestions above are much better. | |
| Jan 17, 2013 at 11:04 | comment | added | Codenamed SC | @JohnU smoothing won't be essential as the voltages are already DC, and it's a 5v regulator which can regulate an input in the range 5v - 18v. I'm not sure about what you mentioned about current, but datasheet says nothing about a minimum value. However the proximity switch is capable of handling a considerable amount of current i guess, at least about 500mA. So it won't be an issue, right? | |
| Jan 17, 2013 at 9:17 | comment | added | John U | 7805 is a power supply, this application relies on the 7805 behaving in an "ideal" way in a situation it's not designed for. Also, this is really not a good approach to solving the problem. The 7805 requires some current to operate (can your sensor source enough current? Does loading it change the sensor performance?) and prefers to see a load to drive into, and a smoothing cap to prevent oscillation / ripple. Anindo's suggestion is quite sensible for your stated application, Photon's answer is OK but assumes a very "clean" signal path (no protection). | |
| Jan 17, 2013 at 6:10 | comment | added | Codenamed SC | Then is there any added benefit in going from 7805 to your solution. I mean is it OK even if i stay sticked to the previous 7805 design? | |
| Jan 17, 2013 at 5:36 | history | answered | The Photon | CC BY-SA 3.0 |