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Topic: Ground bus for a bunch of LEDs? (8) (Read 142 times) previous topic - next topic

HankB

A bunch is eight arranged in a circle 2" (5cm) in diameter. I've already run into some difficulty wiring these so I'd like to share my plans here because I've  gotten some very helpful recommendations.

The LEDs are glued into holes in an acrylic box so the base portion is slightly above the surface of the acrylic. They are mounted on the underside of the lid so some movement between LEDs and connection to a PCB is expected, mostly during construction.

Plans for the supply lead are to bend the leg of the LED so it is parallel to the underside of the lid and a few mm above it. I will solder stranded wire to the leg and then cover the solder joint with some shrink wrap. I also plan to put a dab of hot melt glue on the base of the LED to act as a strain relief for the legs.Near the hinge I will snub the leads to the lid so there is no movement at the LED. (lead, lid, LED... did I actually type all of that correctly on the first try?  ;D ) I will run the leads around the circle, binding them together either with more shrink wrap or zip ties (or perhaps some cable lacing.)

I could do the same with the ground leads, but it seems like a waste of wire since they are all ultimately connected together. I'm thinking about a decent way to provide a common ground connection to all eight LEDs. The first attempt included a bare wire bent in a circle and soldered to the ground leg of each LED. A connection to the one on the end and run to a ground on the processor completes this part of the circuit.

Is a bare ground wire OK? One alternative is to use insulated wire and strip a small section at each LED to expose some bare wire for soldering. That would reduce the exposure of the ground wire. I could paint the solder connection with some liquid electrical tape to further reduce exposure. (It might make sense to paint the supply side of the LED with that too.)

In addition, there are four push-buttons outboard of ring of LEDs which also require ground connections. (The other connection on each push-button goes to a digital input configured with the internal pullup resistor enabled.)

I'm interested in hearing about other strategies that have been employed for similar ground connections. Surely others have faced this same issue.

Thanks!

weedpharma

The only way to have a problem with shorting is to have both wires bare and floating. You are going to insulate and restrain the active wire so no problem wire bare ground. You can wire all ground wires to the ring and use one common wire to connect to Arduino.

I assume the ground ring will be held in place by the LED leads.

Weedpharma

KenF


Paul__B

Using bare, solid wire rather than stranded sounds entirely appropriate for the ground.  If the LEDs are close enough, a common trick would be to bend each LED cathode lead over so that it touches the adjacent one and can be soldered to it.

Stranded wire is used for wire that is going to be flexed - moved about.  Single-strand for wiring that is not going to be moved (such as the power wiring in your house, though even there the ground wire is generally stranded to ensure that breakage of any one strand cannot possibly cause it to disconnect).

My practice - apparently discouraged in some circles but I have always found it the most reliable - is to strip the very tip of a piece of stranded wire, "tin" that then by holding that point with a pair of pliers, pull back the insulation a number of millimetres, twist the strands whilst holding with the pliers, then re-tin the exposed wire and finally whilst it is hot, push the insulation back over half of the tinned part.  This puts the junction of the stiff, tinned area with the very flexible individual strands, well covered with the stiff insulation.

Otherwise, if there is a region of un-tinned wire between the stiff insulation and the stiff tinned area, that part bends back and forth in preference to any other part and readily breaks.  As will be well-know to anyone with experience of repairing equipment.

{The argument goes that flux ingress under the insulation will result in corrosion and/ or degradation of the insulation.  Most of us nowadays however use non-corrosive flux.  Chinese cottage workshops may be the exception.}

CrossRoads

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

weedpharma

Technology from last century ;D

Weedpharma

HankB

Thanks for the suggestions.

I've done some wire wrapping but now have no idea where my wire-wrap tool is. I might have given it to one of my sons thinking I wouldn't use it any more. I would prefer not to be using wire-wrap sockets due to space requirements behind the board. Otherwise I would give it some thought. The LEDs are close enough for the leg of one to reach the next so I think I'll go with that.

I'm using 60/40 rosin core solder. Should I worry about the corrosive effects of the flux? I'm sure this stuff dates to the last century too. ;) (I date to the middle of the last century myself :o )

weedpharma

That solder will probably not be a problem but you can rinse it off with isopropyl.

Weedpharma

Paul__B

Rosin core solder should not be a problem.

Wire Wrap or VeroWire would probably be do-able; you do the wrap close to the base of the LED and you cut off the non-wrapped part of the lead once you have done all the wraps.  By "chaining" the connections (which is exactly what VeroWire does automatically) you have at most two wraps per wire.

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