Audio Interface

Typical Usage

Combine multiple audio signals (radio scanners, laptop audio) and output to Bluetooth transmitters and pre-amp out used to drive amp/speaker.   This will be primarily in a mobile environment.

Requirements

• • Mobile audio interface with the following functionality.

Inputs

2 stereo 3.5mm TRS jacks (with attenuation)

2 mono 3.5mm TRS jacks (with attenuation)

Outputs

2 stereo 3.5mm stereo TRS jacks (line level)

2 bluetooth transmitters (re-purposed)

1 interface to "stackable" amp/speaker?

Power

12v input (TBD, may be lower voltage battery and/or 5v/usb)

• • Integration of functionality

  • Compact size

  • Form factor that easily integrates into external components

  • If attenuation is variable, trim pots internal to the case are acceptable

  • Radio scanners put out at approximately 60 mA.

Logical Diagram

Validate

• • Output voltage of scanners (used to determine level of attenuation)

Proposed Parts (notes only)

• • 10k trimmers:  http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=X262R103B-ND

  • 1k trimmer:  http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=X262R102B-ND

  • 10k resistor: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=RNF1/8T110KFRCT-ND

  • 1k resistor: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=RNF1/8T11KFRCT-ND

  • 3.5mm TRS jacks: http://search.digikey.com/scripts/DkSearch/dksus.dll?vendor=0&keywords=SJ1-3523NG

  • Project boxes: http://stores.ebay.com/Asia-Engineer__W0QQ_sidZ149380788?_nkw=project+box&submit=Search

References

Mixer circuits:

http://www.all-electric.com/schematic/simp_mix.htm

http://www.epanorama.net/circuits/linesum.html

http://www.redcircuits.com/Page53.htm

Attenuation:

http://www.epanorama.net/circuits/speaker_to_line.html