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5.3 Audio Bypass 

In safety critical applications, a bypass system should be included to maintain communications in the 
unlikely event of the 
NEDSP1901 or power 
failing.  The following circuit 
uses a relay to route the 
audio signal directly.  In the 
event that the power fails, 
the Relay will de-energise 
and connect the Input to 
the Output directly.  It will 
be noted that a switch has 
been included to allow the 
signal to bypass the  
Module.      
 
Fig 12. Typical Relay operated audio bypass circuit with user Power Off/Bypass switch 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Summary of Contents for NEDSP1901-PCB

Page 1: ...e not interchangeable although the NEDSP1901 PCB MIC can also be used with line level audio signals Note Go to page 12 for the specific NEDSP1901 PCB MIC information NEDSP1901 PCB Version The NEDSP190...

Page 2: ...or Right angle pin headers or direct wiring This makes a flexible connection arrangement and allows the using to be mounted either vertically or horizontally plugged in or soldered directly to the tar...

Page 3: ...s low as possible supply voltage The power supply input is reverse polarity protected 1 4 DSP Noise Reduction The NEDSP1901 processes the incoming signal and uses known speech and noise patterns to di...

Page 4: ...als into and out of the module are capacitor coupled to ensure that no DC levels are pulled down or shorted when the module is used embodied as part of existing equipment The on board voltage regulato...

Page 5: ...s and mounting hole positions The Jumpers NS0 through NS2 highlighted in Figure 4 are solder jumper pads to allow the user to fix the Nosie Reduction level required Care must be taken so as not to spl...

Page 6: ...o signal and make sure that the 0V pin is grounded correctly with all signal grounds being reference to this pin 2 4 Controls The audio level control potentiometers VR2 Audio Out and VR1 Audio In prov...

Page 7: ...e Reduction Levels 8 Levels of noise reduction are available Noise and tone reduction is shown in the table below Notes 1 When processing signals with high levels of noise using the higher levels of N...

Page 8: ...l in the table containing 3 3 V may be taken up to or left open circuit Level N2 N1 N0 1 0 V 0 V 0 V 2 0 V 0 V 3 3 V 3 0 V 3 3 V 0 V 4 0 V 3 3 V 3 3 V 5 3 3 V 0 V 0 V 6 3 3 V 0 V 3 3 V 7 3 3 V 3 3 V 0...

Page 9: ...erefore if it is intended that the Microprocessor is to drive the 1901 lines High the Microprocessor should be operating from a 3 3 Volt supply as well Alternatively the control signals may be attenua...

Page 10: ...h a Microcontroller Important Note If the Microcontroller is driving the control pins both High and Low it should be operate from a 3 3 Volt supply only If this can t be achieved then consider using e...

Page 11: ...wer failing The following circuit uses a relay to route the audio signal directly In the event that the power fails the Relay will de energise and connect the Input to the Output directly It will be n...

Page 12: ...et or just Electret Capsules Dynamic or Magnetic Microphones These usually have a very low impedance between 30 Ohms and 600 Ohms and provide signal levels of between 55 dBV Pa and 40 dBV Pa As a word...

Page 13: ...d Some devices even have serial data converters built in such that they can be used directly with other digital circuits directly via I2 S these cannot be directly interfaced to the 1901 module Like t...

Page 14: ...trace that joins then Note Do not cut too deep as this PCB has several layers and you may sever traces on the underlying PCB layers Re connecting CH1 G0 is carried out using a solder link The other t...

Page 15: ...etting of 24dB should create a signal of 20dBV by simple addition which should give a signal of about 282mV P P maximum Using the AGC action As previously mentioned the module has an AGC system that m...

Page 16: ...7 97 50 8 943 49 10 03 48 11 26 27 47 12 63 46 14 17 45 15 9 44 17 84 Electret 43 20 02 42 22 46 41 25 2 24 40 28 28 39 31 73 38 35 6 37 39 95 36 44 82 35 50 29 34 56 43 33 63 31 18 MEMS 32 71 04 31 7...

Page 17: ...Page 17 Contact details bhi Ltd PO Box 318 Burgess Hill West Sussex RH15 9NR Tel 44 0 1444 870333 Email sales bhi ltd com Web www bhi ltd com...

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