HBA09-001-70
HB-NEDSP1068
5
6.1.1
Connecting an external microphone capsule or line signal
Locate and identify the jumper J4 (see diagram in appendix A). See the table below for
the correct connections for the different types of microphone.
Pin Designation
Use
Operation
1 I
or
In
External
Microphone
External Microphone or low level audio
input
2
+ or V+
Microphone Supply
Separate Bias Supply 3v3 (3 pin
electrets)
3
0 or Gnd
Microphone Ground
Ground
4
S or Scr
Microphone Shield
Ground
5
O or Ovr
External Overload
LED
External Overload LED facility
6.1.2 Dynamic Microphones
Dynamic microphones tend to have a lower output level than active Condenser Electret
devices, but can have a much more rounded audio reproduction.
To use this type of device, resistor
R7
needs to be removed. This can be found on the
underside of the PCB as shown in photograph in appendix A on page 11. Ensure that
the
PRE
jumper is soldered and the
MIC
jumper is open. The Pre-amplifier Gain setting
needs to be set to 60 dB (links
A
&
B
open, see section 6.1.6).
The microphone connections are then made to MIC IN (J4 pin 1) and MIC GND (J4 pin
3) respectively.
6.1.3 Condenser Electret Microphones
Electret microphones need to be biased either via the third pin or via the microphone
input lead. Both types of microphone have been catered for on the 1068 module. For
self biased devices R7 needs to be fitted. This is nominally factory fitted for 2.2K Ohms,
but may be adjusted as per the following formula:
R7 = 3.3v – 2 v (Mic voltage)
0.5 mA
External biased capsules will need to use the regulated voltage available on J4 pin 2.
This supplies 3v3 for the microphone bias.
The pre-amplifier gain should be set to 50dB for most electret inserts (see section
6.1.6).
6.1.4 External Signal Sources
The microphone input will also accept low level signals up to about 500mV p-p.
However, the pre-amplifier gain should be set to its lowest (40dB) and R7 needs to be
removed.
