Need to change RS232 levels to TTL

[Joe Keaveney]

Hi guys, wondering if any of you have any knowledge of this.

I'm making a board that lights up when the following RS232 outputs are lit:

RTS  DTR   Result
On    On      Green light on
Off    On      Red light on
Off    Off      Lights off

I can't change the choice of RTS & DTR unfortunately.

What I was wondering was if there is a way to change the -12V/+12V RS232 signal levels to the 0V/5V TTL levels that I need for Arduino to read the signals? The various RS232 level shifters/converters don't seem to cater for these 2 pins.

Kind of scratching my head with this one at the minute.

Cheers!

Joe

[Robert Longbottom]

Hi,

Have you looked at the max232 chip?  According to the Wikipedia page ( https://en.m.wikipedia.org/wiki/MAX232 ) ( not my usual go to site for electronics information! ) it can do this.  I've used them in the past for serial to TTL conversion on RX and TX lines and I think the chip has another 2 lines spare on top of that.  I guess you can use them for whichever other signal lines you want / need.

Cheers,
Rob.

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[Steve Netting]

Hi Joe,

Depending on what RS232 device you're using, you may find the signal levels already resemble TTL levels.  I think most cheap USB->RS232 adapters fall into this category, causing some incompatibility with 'old school' devices.  Check the levels, you may be surprised :)

Steve

 

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[Joe Keaveney]

Hi Rob,

Thanks for the info, I'm looking at that as a solution now, just taking the DTR & RTS lines into the R1 IN and R2 IN lines instead, and coming out on the R1OUT and R2OUT lines you think?

Cheers

Joe

[Joe Keaveney]

Haha good point, Steve! I'll get the multimeter out :)

[Robert Longbottom]

Yeah, I don't see why that wouldn't work. (Which quite likely means that it won't work, but its worth a try)  All its doing is shifting signal levels, it doesn't know if they are RX, TX, DTR, or something totally different...

I seem to recall you need capacitors around the chip for it to work correctly.  Other than that from what I remember it was fairly to get working for RX and tx if nothing else.

Rob.

Joe

[Joe Keaveney]

Got the MAX232 ordered already :) Thanks again for the info. This particular device will just receive RS232 signals, nothing coming the other way.

Cheers!

Joe

On Tuesday, July 14, 2015 at 2:59:32 PM UTC+1, Robert Longbottom wrote: