Difference between revisions of "LED Water Wall"

Revision as of 12:41, 15 July 2013

Initial prototype of a smaller version of one of the panels.

Overview

A board member of Huntsville's Downtown 47 and a member of their investment committee approached us on May 28th, 2013 with an interesting proposition. They are "interested in a project to build a wall covered with LED lights that illuminate when the diodes come in contact with water. Our intent is to place the wall in Big Spring Park as a 'water graffiti' exhibit". A similar project was undertaken by Antonin Fourneau in Poitiers, France (video).

Requirements

• The group is willing to spend a decent amount of money to get this built, they don't want to cheap out on the project. They are willing to provide the money for a quality production.
• Our contact thought that 6' by 18' is a good size for the wall, but it is open for negotiation.
• Timeline is flexible; they would prefer that it would be done before it starts getting cold again, but if it takes until next summer, that may be acceptable.
• The exhibit will be transportable, and would not need to be left outside 24/7. It will be pulled out and set up for events as necessary.
• We would likely be able to keep the wall at the shop (only if we want!) to show off when the city isn't using it. (I know there are mixed feelings about this; they will not try to force us to hold it if we don't want to)
• They are very excited about Makers Local and the hackerspace scene, and would love to include us in things like this in the future.
• They are willing to pay for a small demo board to show off how the wall would work, and give us a chance to determine a more accurate budget/timeline before ordering thousands of LEDs.
• Depending on the cost, they are interested in looking into extra features/improvements of the LED wall.
• It needs to be safe (obviously); I don't think this will be an issue, if we take the proper precautions.

Design Decisions

Wall Size

Panel Size

Number of LEDs

Panel Construction

Type of LED

Through-hole, 5mm - LINK

Pros:

• Cheaper (around $0.15)
• Larger "dots" (5mm diameter)
• Can be made flush with surface without epoxy
• If no epoxy is used, LEDs may be easily replaceable

Cons:

• Requires grinding
• Soldering process requires bending two leads and soldering each lead
• Must be soldered by hand
• Some brightness lost due to grinding

SMD (Surface-mounted) - LINK

Pros:

• Assembly is simple and quick: apply solder paste with stencil, place LEDs, heat in an oven
• Brighter (? Depends on the effect of the epoxy and other factors)

Cons:

• Smaller "dots" (<2mm diameter)
• More expensive ($0.41)
• Requires some sort of epoxy to be flush with surface
• LED would only extend ~1/3 of the way through the PCB hole
• With epoxy, LEDs may be harder to replace
• Requires a stencil to assemble

Decision

TBD

Corrosion Prevention

Power Supply

Frame

Cost Estimation

PCB Manufacture

PCB Option 1

40 boards, 500mm by 500mm, 1.6mm-thick FR4, 1oz ENIG plating, black soldermask, white silkscreen

• Quote: $2370 + shipping from Shenzhen (~$60 per board)
• I also got a quote for a limited run of just 5 boards: $684 + shipping (~$137 per board)

LEDs

Frame

Power Supply

Prototypes

Version v0.1 - complete

This 5"x3" 6-LED prototype was made completely in-house. The single-sided PCB was created using an etch-resist mask cut by the vinyl cutter, and the holes were drilled with the drill press. Six blue LEDs and two 3V coin-cell batteries were used to populate the board.

Verdict: Pad shape did not seem to make a difference on water conductivity. Basic circuit idea works very well.

Cost: $0 (used materials that were on-hand)

Version v0.2 - in design

This prototype will consist of 10 6"x6" double-sided PCBs with black soldermask and solder-tinned pads. This prototype will give a better feel for the finished product, and can be used as a sample/demonstration to show off to others. Features that we'd like to see in this prototype are inter-connectivity, water resistance, and overall aesthetics. This prototype will also help provide a better estimate for the time required to assemble the boards by hand. I'm going to try to work in some sort of music controller as well, using parts I have on-hand.

Estimated cost: ~$200 (~$230 with expedited PCB shipping)

• PCBs: Ten double-sided 6"x6" boards, with black soldermask, shipped = $100
• LEDs: 300 C512A-WNS Cree 5mm LEDs from Mouser, white, shipped = $65
• Alternative LEDs: 300 5mm Ultra-bright wide-angle flat-top LEDs, eBay, US seller, shipped = $20
• Connectors: 20 pairs Molex Right-angle PCB connectors, Mouser, shipped with the LEDs = $8
• Other: Optional expedited shipping for PCBs = $30-40

Progress Log

00:56, 11 June 2013 (CDT): Started the wiki page with some PCB cost information. We have also created a small sample prototype to prove the viability of the overall idea. The prototype worked very well, and it seems that the water-sensor shape does not really have much effect on the LED brightness or conductivity of the water.

13:58, 19 June 2013 (CDT): We demonstrated the board and got some great feedback and ideas. We were given the go-ahead to draw up a design for more "finished" prototype in order to give a better feel for the final product and the time it will require to build it. One possibly feasible idea that merits investigation is using the same water pads to control a MIDI (or similar) instrument when water hits the pads.