Gas station without pumps

2012 August 13

EKG blinky boards arrived

Filed under: Circuits course,Printed Circuit Boards — gasstationwithoutpumps @ 22:20
Tags: , , , ,

I ordered an EKG-blinky printed circuit board from OSH Park, on 2012 July 25, and it arrived today, 2012 Aug 13, a delivery time of 19 days, which is not bad for $12.15  for 3 boards (including shipping).  I didn’t even have to create Gerber files, as they accepted the Eagle .brd file directly.

OSH Park’s artistic rendering of the EKG blinky board.

Actual front of EKG blinky board, as delivered.

I’m a little disappointed by the sloppy drill-and-break technique they used for separating the boards, as it leaves rather ugly tabs. I can cut the tabs off with diagonal cutters, but there will still be rough edges left.

I’ll take pictures of all the components tomorrow, and try soldering up the board. If everything works, I’ll try releasing pages for the parts list and assembly. I probably won’t be making kits for this version as I’m already thinking of some revisions.

OSH Park’s artistic rendition of what the back of the board should look like.

Actual EKG blinky board back, as delivered.

I’m a bit worried that I crowded the layout on back here a bit too much for easy soldering. I’ll have to see how tricky the soldering really is.

Some of the revisions I’m considering include

  • A heart-shaped board with symmetric drill holes on the top to make a pendant.  This would require mounting the battery centered, to keep the center of gravity in the middle.  It would also probably double the cost, as the board houses charge for the bounding box.  (Rotating the heart 45° would probably minimize the bounding box, but there would still be more waste than on this board.)
  • Using two LEDs (just below the drill holes?).
  • Perhaps trying a 2-electrode, rather than 3-electrode, EKG (as described by Dobrev et al, the design I copied and cited in the post Medical Instrumentation Chapter 6).
  • Providing different connectors instead of screw terminals for the leads and maybe something other than header pins for the analog output.
  • Using shielded twisted-pair cable for connecting to the electrodes.  It looks like Cat6 STP or SSTP cables with stranded wires would be a fairly cheap choice.  I was thinking of using off-the-shelf CAT6 cables (with the standard RJ45 connectors on the end).  At each electrode I would have a small PC board with two RJ45 jacks and a 4mm snap connector wired to one of the 8 wires or the shield.  That way up to 9 electrodes (counting the ground electrode connected to the shield) could be daisy-chained together.  It’s a cute idea, though it would probably cost about $3/electrode for parts.

    I’m not sure where I’ll find 4mm snap connectors that can be mounted on a PC board.  The snap size is a common one (all the ESD wrist straps use 4mm snaps, as well as most EKG electrodes), but most snap manufacturers seem to have proprietary size schemes which do not include any specs about the size of snaps, and all warn against mixing snaps from different manufacturers, as sizes are not standardized.  My best bet will probably be to go to a craft store that has snap sockets intended for setting in leather (so using posts rather than prongs), and find a socket that fits.  That may be hard to do, as they probably come in blister packs, which can’t be opened in the store for testing.

    One disadvantage of using cat6 cables and RJ45 connectors (other than the price) is that some idiot would undoubtedly try hooking it up to an ethernet port on a computer. It probably wouldn’t damage the computer, but I wouldn’t want to count on that.


  1. […] EKG blinky boards arrived […]

    Pingback by Order and topics for labs « Gas station without pumps — 2012 August 16 @ 23:39 | Reply

  2. can i get your board and schematic files?

    Comment by Salman Sheikh — 2013 August 24 @ 02:15 | Reply

    • I was going to open-source the EKG blinky design, but I’d rather not release the current version, for 3 reasons:
      1) I found a bug in the design. See Blinky EKG hard to debug and Blinky EKG fixed.
      2) I’m planning to do a prettier layout that would make the Blinky EKG be wearable as jewelry.
      3) My class is required to design an EKG circuit as the final lab of the Applied Circuits class, and I’d rather not have them just copying this design—I don’t think this concern will stop me from open-sourcing the project, but the first two will delay me.

      Comment by gasstationwithoutpumps — 2013 August 24 @ 08:19 | Reply

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