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View Full Version : Microphone to Headphones?????



SamMishal
07-16-2009, 10:48 PM
Hi All,
I have just tried the program in the OBEX by Chip Gracey called
Microphone_to_Headphones.Spin
http://obex.parallax.com/objects/57/ (http://obex.parallax.com/objects/57/)
It is·working …but… the quality of the sound output is REALLY BAD………
I am wondering if anyone has tried this program and what kind of quality you achieved.
I am wondering if there is a way to·obtain better quality and if I am doing something
wrong.
·
Samuel
·

CounterRotatingProps
07-16-2009, 11:40 PM
Hey Sam,

have you twiddled the 'bits' setting on line 33?

out of the box, it's bits=11 for sample size@39kHz - you might try 10 or maybe 9, but then you run into the resolution problem.

Are you driving the headphones properly?

- H

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SamMishal
07-16-2009, 11:50 PM
I tried all the settings....it gets better the higher but even on the highest (5) I still get awful quality.....
I am using the headphones amplifier that comes with the Propeller Professional Development Board which
is the exact same thing as the Propeller Demo board.
For the microphone I am using an Electret mic from Radio Shack and the exact same circuit as the one on the
Demo Board....I double and triple checked the circuit and it is as is shown in the Schematic PDF.......
I am interested to see if anyone got the program to work on the Demo Boards and what quality they got....
if with the demo board the quality is good then that means that something is wrong with my circuit or
the microphone I am using.
I do not want to buy a Demo Board just to try this out......I am hoping someone with the Demo Board can try it and
report on the results.........PLEASE...........
Samuel
·
·

Mike Green
07-16-2009, 11:55 PM
The Demo Board microphone input works fine. The ADC circuit is very sensitive to lead lengths, particularly at relatively high conversion speeds and precision. You have to have the resistors and capacitors within about an inch or so of the Propeller chip for it to work properly.

CounterRotatingProps
07-17-2009, 12:22 AM
[oops fat fingered]

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Post Edited (CounterRotatingProps) : 7/16/2009 5:30:00 PM GMT

SamMishal
07-17-2009, 12:26 AM
Mike Green said...
The Demo Board microphone input works fine. The ADC circuit is very sensitive to lead lengths, particularly at relatively high conversion speeds and precision. You have to have the resistors and capacitors within about an inch or so of the Propeller chip for it to work properly.
Thanks Mike.....that makes sense.......I built the circuit myself and the resistors caps etc. are all in the Bread Board
of the PPDB and obviously that is not the best trace setup.....
·
I am going to try and see if I can get a better setup.....otherwise I am going to have to dish out the
money for a Demo Board.
·
Do you think if I built the components and the mic together on a small board and then have
leads that go in the Propeller (and volts and ground) that would work??
·
·
Also I have a small query......the specs of the Mic say it needs 4 to 10 volts....
the schematic as shown on the Demo board is using Vdd (i.e. 3.3 V)...... Could this be causing
a problem?
·
·
Sam

CounterRotatingProps
07-17-2009, 12:27 AM
When you go down to five bits you're going to get bad sound too.

Like Mike said, also your microphone leads need to be short and/or shielded.
Are you getting hum, buzz, distortion, garble, what? What's it sounding like?

Can you scope it?

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CounterRotatingProps
07-17-2009, 12:29 AM
> the specs of the Mic say it needs 4 to 10 volts
> the schematic as shown on the Demo board is using Vdd (i.e. 3.3 V)...... Could this be causing a problem

yes

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SamMishal
07-17-2009, 12:32 AM
CounterRotatingProps said...
When you go down to five bits you're going to get bad sound too.

Like Mike said, also your microphone leads need to be short and/or shielded.
Are you getting hum, buzz, distortion, garble, what? What's it sounding like?

Can you scope it?


I tried all bit settings....it gets better the lower
·
I am getting a slight hum....but it is mainly the distortion and garble that makes the
playback bad.....I can hear the words alright but they are not good quality at all
they are garbled and distorted...but still comprehendible.....

Sam

SamMishal
07-17-2009, 12:36 AM
CounterRotatingProps said...
> the specs of the Mic say it needs 4 to 10 volts
> the schematic as shown on the Demo board is using Vdd (i.e. 3.3 V)...... Could this be causing a problem

yes


Ok .....so that means I have to use 5V but then does that mean that I have to add a resistor between
P8 and the rest of the circuit? P9 already has a 100K but P8 is connected directly....I am guessign the
P8 is the input and P9 is the feedback for the SigmaDelta....or is it the other way round??

Anyway...if I use 5V instead of 3.3 for the Vdd as shown on the circuit then do I also need to add
a 1K between the Pins and the circuit??

Sam
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dMajo
07-17-2009, 12:48 AM
SamMishal said...
·
I am going to try and see if I can get a better setup.....otherwise I am going to have to dish out the
money for a Demo Board.
·

No need for this. I have a Propeller Professional Development Board too. I· (home) made a small·PCB and mounted it between the socket and the propeller to test the ADC functions. It worked much better than on breadbord but still (in my opinion) it is not a hardware ADC (I mean a I2C or SPI IC)

Microcontrolled
07-17-2009, 09:26 AM
On the demo board the sound output sounds like one of those intercoms at Wal-Mart

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Toys are microcontroled.
Robots are microcontroled.
I am microcontroled.


If it's not Parallax then don't even bother. :-)
·

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