Shop OBEX P1 Docs P2 Docs Learn Events
MAX 232 Circuit Components — Parallax Forums

MAX 232 Circuit Components

Shane MShane M Posts: 58
edited 2009-08-31 04:10 in Propeller 1
This· may sound silly.· But the last time I put together a max 232 circuit I had all the components in the same area and didn't actually have to order the parts.

NOW, I'm trying to solder a rs232 circuit onto a propellor board and I am having trouble identifying the parts to purchase from DigiKey.· EVEN the max chip itself.

Has anyone out there order those parts? Can you give me part numbers or links (to any place or site) so I order the right parts?

I used live chat at digikey and they were trying to sell me polarized capacitors.· I know the caps are ceramic non-polarized.· But I still don't know what exactly to get.

Help!

Shane

Comments

  • schillschill Posts: 741
    edited 2009-08-25 14:07
    You should be able to use either polarized electrolytic or nonpolarized ceramic caps, but it depends on the values required for the driver chip you use.

    I think most of the ones I've used recently have been STMicroelectronics ST232 variations - something like this one:

    http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=497-3017-5-ND

    But, I don't have them in front of me to let you know exactly which ones. According to the specs, these can use .1 uF caps so small nonpolarized ceramic caps should be fine.

    I haven't used max232 chips for a while since other alternatives tend to be quite a bit cheaper. The ones I have used had higher recommended capacitance (1uF or 10uF).
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2009-08-25 14:11
    There are all sorts of max232 variants. I like the bog standard DIP part. Type max232 into ebay and it comes up. Or futurlec (though I did accidentally order some surface mount ones recently. Watch those suffixes!). Not sure about digikey.

    The standard max232 uses 1uF caps and these are polarized. Use either tantalum or electrolytic. >=16V. (non polarized 1uF caps tend to be rather large)
    There are variants on the max232 that use 0.1uF caps instead of 1uF, and these would be non polarized caps - and any sort of cap ought to work.

    I just bought another batch of 20 as I've decided that RS232 is the standard connector for all my projects. Old, safe, reliable, but most importantly, you can plug outputs to outputs and short connections and plug connectors into unpowered boards and nothing bad will happen.

    There is the max232 vs the max3232. The first needs 1k resistors in series to do the 5V to 3V translation.

    The different variants are very confusing. Pick one and stick to it!

    Post Edited (Dr_Acula) : 8/25/2009 2:17:29 PM GMT
  • localrogerlocalroger Posts: 3,452
    edited 2009-08-25 14:11
    I just breadboarded one of these onto a demoboard so I can fix you up.· For all the caps I used 0.1 uF ceramic caps digikey p/n 399-4151-ND, and·the chip is a·max3232ECPE chip predictably p/n MAX3232ECPE+-ND.· I copied the circuit from the PropRPM diagram except that I wired both channels up as serial ports instead of the second one to reset for downloading.
  • LeonLeon Posts: 7,620
    edited 2009-08-25 14:15
    The MAX3232 should be used, as it is rated for 3.3 V operation, and can use 100 nF capacitors. The MAX232 requires 1 uF capacitors. I use standard 100 nF capacitors with the MAX3232.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle
  • Agent420Agent420 Posts: 439
    edited 2009-08-25 14:21
    If in doubt, check the datasheets ;-)· They usually offer a std design layout with suggested part values.

    On a side note, you can tap the charge pumps on std 232 type devices for a quick low current negative voltage source... I've done this for dac references and the like.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
  • Shane MShane M Posts: 58
    edited 2009-08-25 14:54
    THANKS SO MUCH everyone! That is a terrific response in a terrific timeframe!
  • hinvhinv Posts: 1,255
    edited 2009-08-25 15:04
    Has anyone here used the max3238, the 8 port variety?
  • Shane MShane M Posts: 58
    edited 2009-08-30 19:12
    Another fast question if anyone is out there.

    I'm using basic 2400 n,8,1 serial·from a PC to the Propeller board.

    The max chip is setup for RX/TX/RTS/CTS.·

    My Question.· Isn't it true that I only really need RX/TX.· The software I wrote·only has pins for rx/tx.·

    The reason I ask is because the 9 pin right angle connection won't solder in since the pins are not positioned for the proto board.· So I was going to cut all but pins 2,3,5· (rx/tx/sig gnd) on the port.· Then I think I can tweak it and make it fit.

    I am 98% sure that will be fine.

    Please respond if you know the answer.

    Shane
  • LeonLeon Posts: 7,620
    edited 2009-08-30 19:19
    The PC can be set up to ignore handshaking. I normally just use TxD, RxD and Gnd.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2009-08-30 23:08
    I only ever use 3 wires. In terminal programs you might find a setting called 'handshaking' and the options are hardware, software or none. Select 'none' if using the 3 wire connection. Also some terminal programs get upset if RTS/CTS are not looped back. As a general rule I join pins 7 and 8 together. And then join pins 1 4 and 6 together. Pin 9 not connected. And then that leaves the 3 pins 2,3 and ground 5.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2009-08-31 01:37
    A MAX233 (ADM233, et al.)·costs a little bit more, but it's worth it because it·doesn't use the external capacitors required with the MAX232 (etc.)
  • Shane MShane M Posts: 58
    edited 2009-08-31 04:10
    Thanks! After checking it out -- I'm not sure why you would mess with the MAX3232 chip?

    I appreciate it.
Sign In or Register to comment.