lesson learned: TRRS audio jacks come in 2 different flavors: OMTP + CTIA
this topic is actually a bit dated ( 2021-04-27 ). i ran into problems when i first tested the KLST_TINY boards. it turns out that the TRRS ( tip-ring-ring-sleeve ) audio jack (
HEADPHONE+MIC aka headset ) comes in two different versions or standards:
the only difference between OMTP and CTIA ( or AHJ ) is the different arrangement of
GND. unfortunately, i carelessly chose the less common ( in my universe ) OMTP standard for KLST_TINY but switched to CTIA in KLST_SHEEP. in summary, if a headset ( TRRS ) is used make sure that it has uses a standard that fits with the KSLT boards. alternatively there are also adapters that switch the arrangement.
a quick research showed that most international manufacturers use CTIA standards and it is often used by the following brands:
- and most android devices
for more information see the wikipedia article on TRRS standards.