RS232 filter [bandpass]

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RS232 filter [bandpass]

Postby SemiconductorCat » Sun Jun 16, 2013 8:09 am

Hi I have to do 5V 232 protocol communication with a noisy device. First of all this is a part of a one big
proximity sensor project.

How could I obtain the equivalent AC circuit and where I could start to design such filter for that.
Baud rate is 1200bps.

Is that IN4148 is needed there?
I'm messed and out of my capabilities and need help.

I'm in a big trouble, If somebody done this already please let me know.
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Re: RS232 filter [bandpass]

Postby Neo » Tue Jul 30, 2013 10:47 pm

The question is not clear.

As I get it, you have two devices to communicate through RS232 and you are expected to be on an environment with lot of interferences. The first thing I would suggest is to use shielded cable. For most of the environments this matches the most.

I would also suggest you to use MAX232 chips on both ends which will keep communication in control. There are some more powerful RS232 chips that increase the voltage levels to keep communication in control.
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Re: RS232 filter [bandpass]

Postby SemiconductorCat » Tue Aug 06, 2013 6:15 pm

This makes me nuts neo sir.
I don't know how to do this. This is completely outside my current capabilities and I don't believe I ever would be
able to design this crap. This is so complicated.

I'll try to a buffer chip to ramp up the voltage. Not sure whether it's a echo ,noise
or EMI. I have already tried those ferrite leads.Where those are necessary, but
whole the electromagnetic system get complicated with then too. I don't know
where to start. How to calculate the parameters that I need.

First I'm start at calculating the noise circuit's thevinin equivalent.Is that my first step
is right? But what and which parameters that I should collect.
Should I take the other end of the circuit as an open end. What impedance should I
assume there.

Whatever the demon is still playing inside the machine! Drives me nuts.
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Re: RS232 filter [bandpass]

Postby Neo » Wed Aug 07, 2013 6:55 pm

Sandun, unlike in analogue communication, digital communication is less prone to distortions such as attenuation. Since RS232 is used here with close proximity, I don't think you need to think that deep to design this. Just start working with two level shifters such as MAX232 and I'm sure those will manage the communication for you. Be sure to use a shielded cable. I'm fully sure this setup can be designed to work without trouble.

You can also look at USB, RS422 or RS485 communication. All of them use differential signalling making them more effective for industrial environments.

See How differential signalling helps suppressing noise

RS 232 / RS485 / RS422 - what's difference?
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