Hybrid cable featuring two data pairs and a power pair? - Page 1
Forum section: electronics / projects

author: Lomax
author_rank: Frequent Contributor
timestamp: April 04, 2017, 03:11:55 pm
content: Hi all,Wondering if anyone here can help me; trying to find a cable with a combination of two twisted data pairs and two heavier gauge power conductors (0.75mm / 18 AWG), but it seems this is a rare beast. I found theBelden 1502R "MIDI" cable, which is perfect in every way, apart from it only having a single data pair. I need two more data connections, and if I have to pull a separate cable for these, I might as well go for something like a CAT5 and a separate two core power cable...

author: Zero999
author_rank: Super Contributor
timestamp: April 04, 2017, 06:11:17 pm
content: How about getting an four pair cable and connect two of the pairs in parallel for power?If the overall screen is thick enough it may also be used as a return connector for power, although this isn't always practical.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 04, 2017, 06:40:31 pm
content: What do you actually need -- what AC properties (bandwidth, impedance and control, crosstalk, etc.), and what cable specs (ampacity or gauge, cost target)?Tim

author: BrianHG
author_rank: Super Contributor
timestamp: April 04, 2017, 06:55:27 pm
content: How much power do you need? I've seen HDMI to Cat-5 cable converters which also feed 75 watts of power with the data on the cat-5 so that you can power a monitor on the other side, with 9gb/sec band-width for the video.

author: mariush
author_rank: Super Contributor
timestamp: April 04, 2017, 08:21:30 pm
content: May seem like a hack (or may be too thick) but you could buy cat6 network cable with awg 23 thickness wires. the pairs are separated by plastic cross throughout the cable, so the voltage pairs won't affect the data pairs as much.Here's an example :http://uk.farnell.com/pro-power/cat6outdoor100m/cable-6-outdoor-use-100m/dp/2580443Won't be quite as good as AWG18 but it would be quite close.

author: free_electron
author_rank: Super Contributor
timestamp: April 04, 2017, 08:25:29 pm
content: usb 3.0

author: dmills
author_rank: Super Contributor
timestamp: April 04, 2017, 09:36:09 pm
content: Talk to an entertainment lighting supplier, you should be able to find a variant of "Scroller cable" that fits the bill (Generally two fairly heavy power cores plus one of two screened twisted pair of 110 ohm impedance.Alternatively the same guys will often have audio cable with a mains line bonded alongside.Some specialist suppliers have exactly what you need, but you will I suspect hate the price.https://www.macartney.com/what-we-offer/systems-and-products/connectivity/stock-cables/powersignal-cable-type-2009b/for example is aimed at the subsea market, with a price to match but fits the bill.

author: Someone
author_rank: Super Contributor
timestamp: April 04, 2017, 10:59:11 pm
content: Do you really need to save the extra copper/weight/size by having the twisted pairs smaller diameter? There are triple twisted pair AWG18 cables as standard items, belden do 1529A and 9553 for instance. Otherwise if you really need a special design you'll need to shell out the money for a custom run (not that expensive).

author: Lomax
author_rank: Frequent Contributor
timestamp: April 04, 2017, 10:59:46 pm
content: Thanks guys! To clarify, the cable will be used in a permanent installation, daisy chaining in-ceiling LED lights with individual dimmers. The power leads will carry 12V, with a total power consumption of about 4A (12x3W LEDs), the first data pair is for a 1-wire interface (separate twinned earth), and the second for two pushbutton input channels (for manually controlling the dimmers). Total wire length approx. 15 metres. Since we're talking about DC power I don't think the data leads need to be shielded, but it can't hurt.

author: Lomax
author_rank: Frequent Contributor
timestamp: April 04, 2017, 11:13:36 pm
content: To those who suggested using multiple pairs in an Ethernet cable for carrying the power - I have considered this, but thought this would not provide enough current capacity. CAT5 is just 22/24 AWG IIRC, but maybe you can get heavier gauge variants?

author: Zero999
author_rank: Super Contributor
timestamp: April 05, 2017, 05:51:38 pm
content: Quote from: Lomax on April 04, 2017, 10:59:46 pmIs it not possible to increase the voltage?Could you go up to 24V or 36V by connecting the LEDs in series? Or does the data pair interface with each of the LEDs or their dimmer circuits?

author: danmcb
author_rank: Regular Contributor
timestamp: April 05, 2017, 06:04:15 pm
content: if you are driving a lot of LEDs the standard way is in series with a current source - more efficient and cable drops don't matter any more.

author: Lomax
author_rank: Frequent Contributor
timestamp: April 05, 2017, 08:02:13 pm
content: Quote from: danmcb on April 05, 2017, 06:04:15 pmQuote from: Hero999 on April 05, 2017, 05:51:38 pmIt's a 12V system, which I hope to power mainly from solar panels. Each LED fixture needs to be individually controllable, and needs to be an off the shelf item. I can reduce the cable length, by doing two separate runs, but the longer one would still be about 10 metres. I also could, if no other cable option presents itself, drop one of the button input buses, which would allow me to use the Belden "MIDI" cable mentioned earlier. Cable thickness is also a consideration; I only have a 20mm conduit, which needs to carry a few other things...

author: Lomax
author_rank: Frequent Contributor
timestamp: April 05, 2017, 08:08:28 pm
content: In other words, each node is self contained, and only needs 12V DC and a connection to the 1-wire network, with an optional push-button control input. I plan to use the same dimmer units for all lighting, not just the twelve in-ceiling lights discussed here, though only the in-ceiling lights will be daisy chained over any significant length.

author: Lomax
author_rank: Frequent Contributor
timestamp: April 05, 2017, 09:06:54 pm
content: Here's what a dimmer node currently looks like - very much work in progress though!

author: moz
author_rank: Regular Contributor
timestamp: April 06, 2017, 03:11:17 am
content: Have you considered a DIY signal-over-powerline setup? One option would be capacitors on the pushbuttons to change the AC conductance while leaving the DC powerline untouched (give or take a microfarad). You could also block that fairly readily at the LEDs if you needed to, but if you keep the frequency low I suspect you won't need to (1kHz rather than 100kHz).The completely opposite setup would be using DC on the pushbuttons and living with any comms glitches that happen when they're pushed. Put a different resistor on each button and measure the voltage drop on your signal wires.

author: Lomax
author_rank: Frequent Contributor
timestamp: April 06, 2017, 10:10:12 am
content: Quote from: moz on April 06, 2017, 03:11:17 amThe LED already flickers at 10kHz; IIRC that is the PWM frequency I found to work best.Quote from: moz on April 06, 2017, 03:11:17 amYes, I did think about this, but have concerns about its reliability over long cable runs. And I should perhaps come clean about where this lighting system will be installed: it's for a 45" steel barge houseboat. Ground iseverywhere.

author: Lomax
author_rank: Frequent Contributor
timestamp: April 06, 2017, 10:14:11 am
content: BTW - I also stumbled upon this statement somewhere:QuoteHadn't thought of that (shielding adding to cable capacitance) - I guess that rules out the Belden "MIDI" cable.

author: vealmike
author_rank: Regular Contributor
timestamp: April 06, 2017, 10:17:54 am
content: Off topic Lomax, given your username and location, might your preferred mode of transport be one wheel short of imperfection?If some too.

author: Lomax
author_rank: Frequent Contributor
timestamp: April 06, 2017, 11:56:50 am
content: You mean something like this?

author: vealmike
author_rank: Regular Contributor
timestamp: April 06, 2017, 12:08:42 pm
content: Yeah, just like that. But without any luxury fittings, like a radio, roof, windscreen or doors. And going backwards.

author: Ian.M
author_rank: Super Contributor
timestamp: April 06, 2017, 12:12:50 pm
content: Take a look at theAutohelm/Raymarine Seatalkprotocol and alsoLIN Bus.You can implement a Seatalk physical layer using LIN transceivers, its reliable over long crappy cabling and doesn't need much in the way of a MCU to transmit or receive it - any 8 pin PIC or ATtiny could handle it, though MCUs with a UART would make it easier.You could also just use the pulse length if you want to do it without a MCU - a 555 based pulser circuit for each button, and the receiver uses monostables or a RC network and comparators to time the pulse and latches the result on the trailing edge.Just for sh-ts and giggles:The mechanic's braver than my one. Even with four wheels he woudn't get in the pit till the vehicle was parked with the handbreak on. I'm surprised that didn't end up with a total FUBAR.

author: Lomax
author_rank: Frequent Contributor
timestamp: April 06, 2017, 12:26:56 pm
content: Quote from: Ian.M on April 06, 2017, 12:12:50 pmThanks, interesting suggestion! However, there are several reasons why I've chosen 1-wire:I will be using Domoticz to control the lighting - it supports 1-wire out of the box.There will be many other sensors and actuators on board, many of which will also use 1-wire.1-wire is designed for low power consumption, simple cabling(!), and flexible topology.

author: Lomax
author_rank: Frequent Contributor
timestamp: April 06, 2017, 12:30:08 pm
content: Quote from: Ian.M on April 06, 2017, 12:12:50 pmAnother good way to multiplex multiple button inputs onto a single line. But it's hard to beat the simplicity of pulling something low - particularly in a steel hulled boat!

author: Lomax
author_rank: Frequent Contributor
timestamp: April 06, 2017, 01:07:05 pm
content: Ok, here's what I think I'll do: I will run a separate 2x1mm2power line down each leg, which will limit the max cable length to ~10 metres. This should solve any voltage drop issues. I'll add a single, unshielded, two-pair cable for the buttons and the 1-wire interface, which loops round at the far end for a ~15m "daisy chain". I think this will be the best compromise wrt cost and conduit "stuffing".

author: Lomax
author_rank: Frequent Contributor
timestamp: April 06, 2017, 01:16:21 pm
content: Aaaand just as a said that, I stumbled upon the Belden 5284US "siamese" cable, which features two 24 AWG twisted pair solid conductors in tandem with two 18 AWG stranded tinned copper power lines in a 5x10mm figure eight configuration.http://www.mouser.co.uk/ProductDetail/Belden-Wire-Cable/5284US-010500Hmmmmmmmm.

author: Lomax
author_rank: Frequent Contributor
timestamp: April 06, 2017, 01:22:55 pm
content: Question: considering that the 1-wire interface is single ended, and there will be a separate 16-18 AWG ground wire for the power supply, is there any benefit with using twisted pair cabling for the data line? Won't the power GND negate any benefit of having the 1-wire line twisted with a separate GND, by preventing the GND reference shifting along with the data level?

author: Ian.M
author_rank: Super Contributor
timestamp: April 06, 2017, 04:09:34 pm
content: You would do best to semi-isolate the grounds - use 12V for the gate driver and load circuit, with an optocoupler between the BAE0910 output and the transistor bases, then run everything else relative to the data twisted pair ground with a choke on the regulator input so its input decoupling cap doesn't couple the 12V power line noise into the data ground.That will tolerate a lot of drop in the power/ground wiring.

author: Lomax
author_rank: Frequent Contributor
timestamp: April 06, 2017, 04:46:48 pm
content: Quote from: Ian.M on April 06, 2017, 04:09:34 pmThis sounds like a great idea, thank you! I was wondering if there was a way to keep the BAE0910 ground reference "floating" with respect to the power GND. But are you saying I should ground reference the buck converter to the data pair's GND, or the power line GND? And does "use 12V for the gate driver and load circuit" mean I should connect the high side of the gate driver to 12V, or just connect the low side to the power line GND? Sorry, but this kind of design is a little unknown to me - I understand the principle, and its benefits, just confused about correct implementation!Edit: Oh, and should the TVSs on the digital side dump to data ground or power ground?

author: CM800
author_rank: Frequent Contributor
timestamp: April 06, 2017, 05:27:36 pm
content: Have a look at IGUS and cables for automation.There are a lot of cables out there designed for power + twisted pairs, usually used with CAN or EtherCAT with power for motors with integrated drives.

author: Ian.M
author_rank: Super Contributor
timestamp: April 06, 2017, 06:20:47 pm
content: The ONLY connection that joins the two power domains on the board should be the choke feeding the regulator. All the control side grounds including the 5V regulator would be data ground. This does however mean the data ground wire will carry the control logic ground return current, but as the BAE0910 only draws 8mA max, if you use a high CTR optocoupler, you can keep the ground return current under 10mA. You've already got clamps on the data lines (though you should insert a resistor between BAE0910 pin 4 and clamp diode D4) so even if one board looses its data ground, resulting in its data line trying to rise above 5V, it wont damage the other boards.The load circuit and gate driver would operate between +12V and power ground. Put the opto's phototransistor directly between +12V and the bases, with a pulldown resistor to power ground for turnoff.Put the opto's LED between R4 (change to 1K8) and data ground.This has the side benefit of giving the MOSFET 12V gate drive, so it turns on harder - you can probably use a cheaper MOSFET that isn't low Vgs threshold and still get very low losses.Stick a 22R resistor in series with C1 - its kinder to the MOSFET. You should also put a fast anti-parallel diode across the load, cathode +ve as a back-EMF surpressor in case an inductive load is ever connected.

author: Lomax
author_rank: Frequent Contributor
timestamp: April 07, 2017, 12:08:36 am
content: Thanks Ian, that's one hell of a reply - answering all my questions, confirming things I wasn't 100% sure about, even expanding to suggest additional enhancements - I wish I could press "Say thanks" many times overQuote from: Ian.M on April 06, 2017, 06:20:47 pmWhich should be fine, since power usage on the control side is quite small. I wonder though, if this might be a problem should there be be a significant spike, e.g. from a nearby lightning strike? EMF design guidelines seem to emphasise the importance of a low impedance route to ground from the TVS diodes - which makes sense, but which a single 24 AWG conductor in a 15mtr twisted pair isnot.Quote from: Ian.M on April 06, 2017, 06:20:47 pmI had already started looking for a high CTR opto on Mouser, thinking that would be needed - good to know I was on the right track! Opto-transistors don't have many parameters of interest, but man there are many models to choose from. I have exhausted myself looking at datasheets, and have selected the Sharp PC367NJ0000F, more out of boredom than anything else - it does provide 10mA Ic @ 2mA If, which is way up there, but so is the price; £0.45 each @ 25pcs.Quote from: Ian.M on April 06, 2017, 06:20:47 pmRoger that!Quote from: Ian.M on April 06, 2017, 06:20:47 pmDone.Quote from: Ian.M on April 06, 2017, 06:20:47 pmAnd done.Quote from: Ian.M on April 06, 2017, 06:20:47 pmNot 100% sure I understand what you mean here.Quote from: Ian.M on April 06, 2017, 06:20:47 pmDone.Quote from: Ian.M on April 06, 2017, 06:20:47 pmYep, I'll take a look - the one that's on there was picked for its 2V threshold and low Rds.Quote from: Ian.M on April 06, 2017, 06:20:47 pmDidn't know that. Done.Quote from: Ian.M on April 06, 2017, 06:20:47 pmThe suggestion of adding an EMF suppressing diode across the output is excellent - the exact same circuit can then be used to control things like small fans (e.g. PC axial fans). Thank you. I'm guessing the same PMEG3020 Schottky I use for polarity protection should work here? I took the liberty of adding a small 100pF cap as well, to limit dV/dt in such use.This is quickly turning into the most complicated design I've tackled so far - but it does feel like it's on the right track. Not looking forward to the board layout; first time putting a buck converter on-board, and first time having two different ground references!Edit: The TPS560200 buck converter is now starting to look ridiculously over-spec, with its 500 mA output. I should look for somthing smaller...Edit: R5 moved "inside" the TSV, and increased to 150 Ohm.

author: Ian.M
author_rank: Super Contributor
timestamp: April 07, 2017, 01:07:18 am
content: Sorry about that - I meant pin 5 DQ for the extra resistor, so when the clamp is clamping a surge, the current into the IC pin is limited, otherwise you'll blow out the internal protection diode before the clamp conducts. The SMF5.0 datya says it breaks down at 7.0V and clamps at 9.2V. The BAE0910 I/O pin currents must be limited to +/-25mA, which would drive DQ to one diode drop outside the rails, so either you need 140R between the clamp and the pin, or if the source current it is clamping is limited enough to get the voltage down to just above 7V, at least 52R. Adding Schottky clamps right at the DQ pin eases this limitation by bypassing the internal clamp diodes allowing you to decrease the resistor and then the only issue is the charge storage in the 20uF bulk capacitors. It can only cope with a 0.8V rise before the BAE0910 max Vcc is exceeded, which can handle a surge of 160mA current into the pin to rail clamp for only 100us (30R resistor). Obviously more bulk capacitance helps extend the permitted surge duration, or providing an active clamp at the pin to keep the 5V rail from rising.I don't think the 'bounce' when the TVS diodes shunt ESD to the data ground will be an issue. The choke on the regulator input will block it long enough for the chrge to dissipate, and everything else sees the same common mode voltage. If you are feeling paranoid, put a 12V bidirectional TVS diode between the data and power grounds.

author: Lomax
author_rank: Frequent Contributor
timestamp: April 07, 2017, 12:41:16 pm
content: Thanks Ian, although much of that is beyond me, having a protective resistor on DQ makes sense. I have updated the schematic, but opted to remove R9 and move R5 "inside" the TVS while increasing its resistance from 47R to (stock) 150R. I had put R5 "outside" the TVS after reading that a TVS needs some minimum impedance to work against. In my application I expect that to be provided by the cabling anyway.Edit: Further discussionmoved to a separate thread!