Hmmm, after reading the Whimsical response to this issue, if there is in fact no current-limiting resistor between the -12V power rail and the normalling connection on the RUN jack, then it is pretty clearly a design mistake in JF and a more straightforward
mea culpa from Whimsical might have been better, rather than blaming a lack of standards.
To re-quote what Olivier Gillet said about this issue in another thread:
pichenettes wrote:I think the designer(s) of the JF wanted to normalize the "Run" input to -12V so that it was set to a known, easily detectable voltage when nothing is patched in the jack (detecting unpatched jacks is tricky indeed).
The issue of doing it by connecting the "switch" of the jack straight to -12V is that there is a temporary short to -12V during the insertion of the jack, which can cause the module on the other end to send an excess of current, and exceed the current drive capability of an op-amp or GPIO. A more sensible choice would have been to insert a small resistor (2 or 3k is low enough) between the -12V rail and the "switch", so that, in the event of a short during insertion, only (12 - -12) / 2k = 10mA of current is at most sourced or sinked on either sides. In normal operation, this would cause only a small voltage drop (100/102 x -12 = -11.7V).
I made a similar mistake early in the genesis of Tides, though I found it before the module went in production.
Most module manufacturers will design the outputs of their modules to be safe against shorts to ground, but expecting them to make all their outputs safe against connection directly to one of the power rails, which seems to be the case with JF, is a bit much and a very unsafe assumption.
Here's part of the Tides schematic for an input which has normalling to one of the power rails. Notice the 2.49k resistor (R60) between the power rail and the normalling connection on the jack socket. That's what seems to have been omitted from JF, although we can't be certain because no schematics are available for it.
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