Figure 50: PWM Example Schematic
2.18.3 Unused PWM Signal Termination
Unused PWM signals can be left unconnected.
2.19 Analogue Audio
2.19.1 Analogue Audio Signals
If only single channel (mono) line input or headphone output is required, it is recommended to use
the left channel.
Table 31: Analogue Audio Signals
2.19.2 Reference Schematics
Depending on the module, the headphone output signals can have a DC offset. Since the Apalis
standard does not provide a virtual headphone ground, series capacitors are needed. If the
headphone output signals are used only as line output signals, 1µF series capacitors are sufficient.
If the signals are used for driving headphones, larger capacitors (47µF and more) are
recommended.
The line-in and microphone signals do not require serial capacitors since they are already placed
on the module. Some microphones (e.g. the widely used electret microphones) require a phantom
power. The reference schematic below shows a suitable solution for common electret microphone
capsules. Please note that some microphones require that the phantom power is provided on the
middle ring of the 3.5mm jack while others need to be powered over the tip of the 3.5mm jack
which is also used for the audio signals.
The Apalis module features separate ground pins for the analog interfaces (AGND). These ground
pins are connected to the regular ground on the module. Therefore, a connection between AGND
and GND (over a ferrite bead) is not required on the carrier board. Try to route the headphone
ground with a separate trace from the module ground (star ground philosophy). This avoids
conductive coupling between the return current of the headphone output and the microphone
input.
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