i use sm8223 as fsk decoder it has serial output data ,And i connected my circuit to serial port on my computer via MAX232 and it works well and I have the caller ID on my computer, but there is problem, that is there noise sound on my phone line appear as i connect my computer with circuit,
can any one help me to clear phone line noise

thank u in advance

 

Hi alitex,

I think that the problem could be the power supply you're using for the decoder chip. Your copy of the app note out of the datasheet tells me nothing about it. If you're using a DC supply with insufficient filtering, you can easily get 60 hz hum or other noises on your phone line.

Try this. Temporarily run your circuit from either a well-filtered lab power supply or from batteries that you combine to get the proper voltage for the IC chip. If the noise goes away, then you'll know it's your power supply for the IC. And if so, you can easily take care of it by putting a large capacitor across the power supplies DC output. Try 470 uF or 1,000 uF electrolytic. But make sure that the cap voltage is higher than the power supply voltage. You could also have a problem with 'pickup'. Things like florescent lights and other household circuits plugged into the 120 VAC line radiate signals that often get picked-up as hum or other audio at the rep rate of the circuit. Make sure all your wires for the circuit are as short as possible and place the circuit in a metal box.

If you need more help, please draw a schematic and upload it. Make sure it's readable.

Good luck,
Kamran Kazem,
kkazem

 

Hi alitex,

I think that the problem could be the power supply you're using for the decoder chip. Your copy of the app note out of the datasheet tells me nothing about it. If you're using a DC supply with insufficient filtering, you can easily get 60 hz hum or other noises on your phone line.

Try this. Temporarily run your circuit from either a well-filtered lab power supply or from batteries that you combine to get the proper voltage for the IC chip. If the noise goes away, then you'll know it's your power supply for the IC. And if so, you can easily take care of it by putting a large capacitor across the power supplies DC output. Try 470 uF or 1,000 uF electrolytic. But make sure that the cap voltage is higher than the power supply voltage. You could also have a problem with 'pickup'. Things like florescent lights and other household circuits plugged into the 120 VAC line radiate signals that often get picked-up as hum or other audio at the rep rate of the circuit. Make sure all your wires for the circuit are as short as possible and place the circuit in a metal box.

If you need more help, please draw a schematic and upload it. Make sure it's readable.

Good luck,
Kamran Kazem,
kkazem

ok i took your opinion into account,for the power supply i used good one without noise, i put alot of capacitor that has alot of valus but i can't solve it...
my only problem is when i connect any pin of com port in my computer with my circuit happen that(noise in phone)