Creator Ci40 Microphone & Stereo Inputs
by pevans9463 in Circuits > Electronics
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Creator Ci40 Microphone & Stereo Inputs
The Creator Ci40 platform, available from RS and Mouser, is designed to allow developers to easily create connected projects based on MIPS hardware. For more projects, documentation and open-source code for the Creator Ci40 check out www.creatordev.io
In this instructable we investigate several modes in which the Creator Ci40 board can be used in audio related projects. The article covers:-
1) Using headsets & microphone
2) Feeding stereo audio from other sources
3) Stereo microphone or audio source input
4) Creator Ci40 audio input configuration options
...........a. Headset microphone connection
...........b. Microphone Plug-In-Power
...........c. Audio input gain control
5) Appendix
...........a. Audio input electrical parameter summary
.
What you'll need
-- 1 x Creator Ci40 board
Using Headsets With a (Mono) Microphone
By default the Creator Ci40 is supplied configured for mono
microphone input on the 3.5mm headset socket CN12.
The CN12 microphone connection has Plug-In-Power (PiP) (also known as Phantom Power) for powering a standard electret condenser microphone.
Additionally the Creator Ci40 also has an audio pre-amplifier for providing extra gain when using microphones. The pre-amplifier is enabled using switch SW3.1 (refer to the Board Configuration Options later in this article)
The Creator Ci40 headset socket has 4 contacts and is configured for use with CTIA standard headsets. If you have a headset that is OMTP standard you need to use an OMTP-CTIA adaptor which are readily available.
Feeding Stereo Audio And/or Microphone Signals From Other Sources
If you want to feed stereo audio into the Creator Ci40 from another source, such as a mobile phone, tablet, or stereo microphone you can use the on-board stereo audio ADC.
The Creator Ci40 has a stereo audio ADC. The inputs to the ADC are accessible via pads on the underside of the PCB. Stereo audio signals can be fed into these pads.
Note: Some re-configuration of the Ci40 board may be needed depending on your application.
Connections:
Pad Reference.........................................Signal
TP40.........................................................Audio LEFT Input
TP41.........................................................Audio RIGHT Input
TP42.........................................................Audio Ground
A typical connection to TP40, TP41 and TP42 is shown in the figure.
Use of screened cable is recommended to minimise noise.
Creator Ci40 Audio Input Configuration Options
The microphone input on the headset connector CN12 is connected to the audio ADC LEFT Input. If a standard stereo headphone jack, with 3 contacts, is inserted into CN12 then the microphone input will be shorted to audio GND so the LEFT input channel will not function.
To allow simultaneous use of stereo headphones and stereo audio input the microphone connection from CN12 should be disconnected using R94
R94............................Function
0R..............................12 Mic input connected to audio LEFT input (Default)
Not Fitted...................CN12 Mic input disconnected
Microphone Plug-In-Power
Both LEFT and RIGHT audio inputs have Plug-In-Power (PiP). PiP provides a low current dc supply, in this case at 3.3 Volts, to power microphones and this voltage shares the same conductor as the audio.
Most audio sources will not be affected by the PiP voltage. However if you experience issues with your audio source then the PiP can be disabled using R62 and R93
R62..................R93...................Function
2.2k..................____.................RIGHT Audio Input – PiP Enabled (Default)
Not Fitted.........____.................RIGHT Audio Input – PiP Disabled
_______...........2.2k..................LEFT Audio Input – PiP Enabled (Default)
_______...........Not Fitted.........LEFT Audio Input – PiP Disabled
Audio Input Gain Control
The audio ADC has a pre-amplifier which can provide an additional
+15dB gain for use when connecting to microphones or other low level audio sources.
The pre-amplifier can be enabled using SW3.1
SW3.1...............................................Signal
OFF...................................................Pre-Amplifier gain 0dB (Default)
ON....................................................Pre-Amplifier gain +15dB
SW3.1 should be set ON when using headsets or microphones. This is not the default state
SW3.1 location is shown in the figure
Audio Input Electrical Parameter Summary
Parameter..........................Value....................Condition
Audio ADC......................................................AKM AK5720VT 24bit
Max input signal level........2.0 Vpp.................Pre-Amplifier OFF (0dB)
(0dBFS digital level)..........0.35 Vpp...............Pre-Amplifier ON (+15dB)
Input Resistance...............>2kΩ....................PiP Enabled
..........................................>15kΩ..................PiP Disabled
PiP voltage........................3.3V......................PiP Enabled
..........................................None.....................PiP Disabled
Input coupling.................................................Both channels are AC coupled into the ADC
Special thanks to hardware engineer Pete Money from the Creator team for his efforts in putting this article together.
Find Out More
If you'd like to find out more about the Creator Ci40, documentation, projects and source-code, check out
.
Creator Ci40 boards can be purchased from Mouser or RS