Kenmore 158 UI: Power & Data Cable

The Arduino Mega behind the LCD panel communicates serially through the Serial1 hardware, leaving the USB connection available for its usual console + program loading functions. The cable also carries +7 VDC for the Mega’s on-board regulator, plus a few bits that might prove useful, and enough grounds to be meaningful.

The pinout on the DE-9 female back-panel connector:

  1. TX (Mini -> Mega)
  2. RX (Mini <- Mega)
  3. Current sense amp
  4. D4 Enable ATX
  5. Gnd
  6. +7V regulator
  7. Gnd
  8. Gnd
  9. Gnd

Which looks like this:

Kenmore 158 UI - cable at motor controller
Kenmore 158 UI – cable at motor controller

One could argue that I should use insulation-displacement connectors and pin headers, but there’s something to be said for a bit of meditative hand-soldering.

The 7 V supply drops about 90 mV through its slightly too thin wire. With current around 100 mA, that works out to 900 mΩ, including all the connectors and gimcrackery along the way. Close enough.

More cogently, one could argue that I should have used a DE-9 male connector, so as to remove the possibility of swapping the cables. So it goes. The pinout attempts to minimize damage, but ya never know.

The green jumper on the Mini’s serial pins reminds me to unplug the UI cable, lest I plug the USB adapter into it and put the serial drivers in parallel.

The 7 V regulator stands over on the left, powering both the Arduino Pro Mini and the Mega + LCD panel. My thumb tells me that piddly little heatsink isn’t quite up to its new responsibilities, unlike the now vastly overqualified heatsink on the ET227. On the other paw, that’s why I used a pre-regulator: so that same heat isn’t burning up the SMD regulators on the Arduino PCBs. Time to rummage in the Big Box o’ Heatsinks again.

4 thoughts on “Kenmore 158 UI: Power & Data Cable

  1. Do you worry about the conductors breaking at the ends of the D-9’s solder cups? I often “pot” such a connection in a slightly rubbery flavor of hot-melt glue, figuring that the ribbon cable is going to be less prone to breaking 1/4″ away than the bare wires at the ends of the solder joints.

    The PCB end of the cables are hand-soldered to pins and individually heat-shrunk? Very nice technique there. I do the same but maybe not always quite as tidily. :-)

    1. the conductors breaking at the ends of the D-9’s solder cups

      I generally close my eyes, hold my nose, and ignore that whole issue. Obviously, they’re intended for use with a connector housing or inside a never-opened case, but I haven’t had any problems to speak of.

      maybe not always quite as tidily

      Documenting this stuff has definitely up-amped my attention to detail. For the stuff that gets shown off, anyway… [grin]

  2. there’s something to be said for a bit of meditative hand-soldering

    And not to mention reliability in an actual connection! I recently bought 4 50-pin ribbon cables using IDC connectors from ebay/China … you guessed it, all had at least several pins that were not reliable when slightly wiggled. I have since purchased the much more reliable AMP IDCs to replace the ends with. I don’t have a choice on either end but to use the 50-pin headers, but I’m not about to solder that many connections to a connector with pins! Price those same cables from Digikey!

    1. I generally use heat shrink on each connection or a hood with a strain relief but hot glue does work very well as a strain relief.

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