M2M CONTROL C660 - Technical Manual V2.00
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Page 18 of 36
Hands-free connector
The C660 unit has a 4-pole 2.5mm jack connector for connecting a hands-free set to the built-in
GSM modem. The speaker output is amplified through the internal Class-D amplifier and is a
differential (balanced) signal. A loudspeaker of 4/8 Ω can be connected directly to the speaker
output. The microphone input is differential in order to minimize GSM (TDMA) noise. An audio
line transformer must be used to convert the signal to a single ended signal, when connected to
external equipment that does not have a differential (balanced) input. Otherwise the GSM noise
will not be suppressed / cancelled, and will pass through all the way to the loudspeaker.
The microphone signal is biased internal for active microphones.
4 pin headset connector overview
Pin
Name
Description
1
Mic +
Microphone positive Input
2
SPK +
Speaker positive output
3
Mic -
Microphone negative input
4
SPK -
Speaker negative output
Microphone characteristics
Parameter
Min.
Typ.
Max.
Unit
Working voltage
1.65
1.8
1.95
V
Working current
20
1000
µA
Speaker characteristics
Parameter
Min.
Typ.
Max.
Unit
Working voltage
3.5
3.8
4.2
V
Output power (THD+N=10%)
0.83
2.05
W
Please consult the M2M CONTROL IDE documentation for more information on using the Hands-
free interface.
External voice output
A voice audio output is available on X2 connector. Digitized audio can be played through this
output by the application interface. Please consult the M2M CONTROL IDE documentation for
more information about enabling the xVoice output, and playing digitized voice messages.
The output is at line-out level (3Vpeak-peak), and internally shared with GSM voice line.