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MAX232 (RS232) based Serial to Propeller interface - how safe ? — Parallax Forums

MAX232 (RS232) based Serial to Propeller interface - how safe ?

RizThomasRizThomas Posts: 24
edited 2009-01-21 22:45 in Propeller 1
Although I have built the Parallax Serial to Propeller Interface which works great in place of my USB propplug, I came across a MAX232 Serial to Propeller circuit (WWW.tdus.de) incoporated a Prop D-40 board.

Question: Are the signal levels safe for the Propeller. I seem to remember that for 3.3V circuits, they recommend to use the MAX3232 ic which is the 3.3 volt version of the chip.

I can only find MAX232 chips here locally unless I order·the MAX3232·from the US.

Comments

  • Dr_AculaDr_Acula Posts: 5,484
    edited 2009-01-21 07:31
    Well - you *could* use max232s with voltage dividers and/or with other techniques others will no doubt be able to suggest.

    The max3232 though is the neater solution. I got some from http://www.futurlec.com I'm in Australia and Futurlec ship out of Thailand so their shipping time is about 8 working days whereever you are.

    $1.90 each, postage for small quantities is a flat $4. I buy about 2 orders a week because their shipping is so low you can afford to get a few test chips then come back and get more if they work fine.

    Post Edited (Dr_Acula (James Moxham)) : 1/21/2009 7:37:26 AM GMT
  • virtuPICvirtuPIC Posts: 193
    edited 2009-01-21 08:16
    Well, you can also order MAX232 from the US at a price lower than $0.90 per piece. The TI ones are much cheaper than the Dallas ones.

    Regarding the voltage levels have a look at the hardware stickies in this forum: 'HOW TO SAFELY INTERFACE A 5V SIGNAL TO THE PROPELLER?' I would not connect it directly to RS232. Stay with the MAX232 or build a converter yourself from two transistors and a few resistors.

    virtuPIC

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  • QuattroRS4QuattroRS4 Posts: 916
    edited 2009-01-21 10:14
    Have a look at these two options .. from 'St Microelectronics' and 'Intersil' - Both are Max3232 drop in replacements .. and are 3v - 5.5v devices.

    I have included pdf's for both.

    The ST Microelectronics option is available from Radionics - radionics.rs-online.com/web/
    Specifically - radionics.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=4152111

    The Intersil version is available from Farnell - www.farnell.com/
    Specifically - ie.farnell.com/intersil/icl3232cpz/rs232-transceiver-3232-dip16/dp/1201546

    Incidentally I have used both without issue.

    Hope this helps..

    Regards,
    John


    Edit: As a reference I have added a·Pdf of the the RS-232 PropStick schematic as used by parallax.

    Rgds,

    JT

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    Post Edited (QuattroRS4) : 1/21/2009 10:29:07 AM GMT
    pdf
    pdf
    ST3232.pdf
    86K
    pdf
    pdf
    ICL3232.pdf
    657K
    pdf
    pdf
    PropStick-v1.2.pdf
    1M
  • RizThomasRizThomas Posts: 24
    edited 2009-01-21 15:22
    Thank you for all the replies. I needed these info to clear up some things in my mind.
    The links and files are very helpful
  • virtuPICvirtuPIC Posts: 193
    edited 2009-01-21 22:45
    ...and here is another link: www.parallax.com/tabid/254/Default.aspx. The second image headlined 'Serial to Propeller' shows a level converter Propeller to RS232. I knew that I've seen a schematic for a discrete converter recently... smilewinkgrin.gif

    However, I would put diodes in parallel to the resistor between basis and emitter of the transistors taking RS121 as inputs. Haven't looked up the datasheets but usually they don't like negative VBE.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
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