Pulse Necklace 08Oct2009

Hack Notes, Pulse Choker, Oct 8th 2009

Problems:

• connection problems - fabric to wire. Fabric to LED.
• hot glue bleeds into fabric, making soldering impossible
• conductive thread frays easily and ends cause shorts
• if traces touch skin, ECG measurement is hosed
• circuit stencil has parallel LED problem - need new design
• conductive paint is hard to paint, expensive, bleeds
• ECG still doesn't work with fabric strap
• pendant way too big
• need batteries & holder - coin cells logical choice
  • can't find pack's that hold more than one
  • http://www.sparkfun.com/commerce/product_info.php?products_id=8822

Things that worked well:

• velcro clasp
• ECG circuit from open-ecg-project (on Eric only?)
• silver paint stencil looks good

Possible Steps Forward:

• use surface mount LEDs
• try putting paint on plastic fabric
  • does this make washing awkward/impossible?
• try using bias tape as replacement for solder connections
  • do a tensile test
• use snaps / metallic clasps as replacements for solder connections
  • still need to hold fabric flat somehow
• try laundering the silver paint!
• back to copper paint: it's too thin, we could just leave it open to dry out a bit
• can we make graphite paint work somehow?
• can we make one entirely with conductive thread?
  • Would force us to use through-hole parts
  • for LEDs, make little hoops from wire legs
  • for connection to wires, use jewelry hoops, then solder to them
  • try using conductive thread in a sewing machine?
  • do they sell snaps with hoops? - lilypad inspiration...
  • check out things at Jewelry store...
  • can also just stitch the LEDs in, leaving rest of display with paint...
• make new stencil
• can we iron stuff unto the conductive paint areas? e.g. ironing on the backing
  • need to do ironing step before you do soldering of LED step

Laundering Experiment

• we dug out our old, simple display, with just the three LEDs. Turns out, the traces on it are already unreliable, due to cracks in the silver paint where the fabric has been bent.
• after rinsing in water, the traces were still as good as before at conducting. The wet fabric does not conduct.
• after soap wash, traces are still great - so the silver paint does survive washing

Ribbon Snap Testing

• we tested a ribbon snap on two conductive paint traces - worked like genius!
  • we think it wouldn't work so well on conductive thread unless you made a big mess of thread at the connection point
• ribbon snap super strong
• but hard edge in contact with soft fabric makes a natural bend point - and those are bad for electrical connection of the paint.

What do we need for next time?

• more silver conductive paint - buy another one, we'll need it anyway... Chung-Hay will buy.
• disposable plastic plates to "air out" and evaporate the copper paint - Eric will bring.
• Chung-Hay will bring "Jewelry hoops"
• Eric will look into suitable ribbon snap part - bigger, single row
• Eric will look into TH LED parts - super bright, diffused lens, <=3mm, wide viewing angle
• Eric will look into battery holders for coin cells - 2 or 3 in holder! 1062K-ND