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Circuit suggestions for counting pulses through audio jack

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doncarlosalbatros

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I want to send pulses coming from a device to a smart phone through its audio jack.

I dont know where to start with.

What considerations should I look into?

I mean my idea was to count pulses so on off voltages appearing at the audio jack and read the freq. by an app.

How can I achieve the analog part? Does anyone have experience with this?
 

Hi,

each design begins with specifications.
This are values with units. Maybe additionally tolerance.

A pulse maybe is defined with
* low voltage (min, max)
* low time (min, max)
* high voltage (min, max)
* high time (min, max)
maybe additionally risetime, fall time...or anything else...

you say counting.
Counting with limited time? Or inifinte?

Klaus
 

Counting part will be done by software. Im just asking an interface between pulse train coming from LM331 and smart phone audio jack. I can adjust pulse freq. Between 100Hz upto 10kHz. I need an interface which converts 0..5V pulses with 1kHz to 0..10mV clean pulses which will go to iphone's audio jack. I guess iphone's mic input impedamce is 600Ohm.
 

Hi,

I need an interface which converts 0..5V pulses with 1kHz to 0..10mV clean pulses which will go to iphone's audio jack. I guess iphone's mic input impedamce is 600Ohm.
Click to expand...

What about two resistors as voltage divider? 300k, 600R
If there is 600Ohms input impedance, than use: 150k, 600R

Klaus
 

How about the noise at that mV level pulse amplitudes? Im afraid of glitches. Should I use a low pass filter. I want clean pulses since they will be 10mV amplitude with varying 100Hz to 1kHz freq.
 

Hi,

specify the glitches, specify the noise, specify "clean", then we can discuss.

A 150k/600R voltage divider won´t introduce considerable noise.
A 150k/600R voltage divider won´t introduce glitches.

So if there are glitches or noise then will come from some (to us) unknown source.
If you are afraid of glitches ... I assume you know the source.

Klaus
 

Oh okay if the divider wont introduce glitches so I dont have problem.
 

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