Shop OBEX P1 Docs P2 Docs Learn Events
Max232 potoboard interface — Parallax Forums

Max232 potoboard interface

Ole Man EarlOle Man Earl Posts: 262
edited 2008-07-02 02:26 in Propeller 1
Here is a how-to for interfacing a Parallax PROTO board to a PC's serial port.

Parts:

1 - MAX232
4 - 10 uf Electrolitic Caps 5vdc or larger
1 - Parallax proto board
1 - 9 vdc wall wart for powering protoboard

Pinouts:

Max232 and DB9 Pins:

16 > Protoboard 3.3 vdc
15 > Protoboard VSS (Ground)
14 > Pin 2 of DB-9 Female Connector· for PC serial port
13 > Pin·3 of DB-9 Female Connector· for PC serial port
12·> Protoboard P31 TTl TX
11 > Protoboard P30 TTL RX
9··> Protoboard·USB2SER pin 4 (reset pin)
8· > Pin 4 of DB-9 Female Connector· for PC serial port
1 <> 3·· 10 uf Cap + on pin 1
2 <> 16· 10 uf Cap + on pin 2 .... neg of Cap on Pin 16 (3.3 vdc vcc)
4 <> 5··· 10 uf Cap + on pin 4
6 <> 15·· 10 uf Cap + on pin 15
Pin·5 of DB-9 Female Connector· for PC serial port <> Pin 15 of MAX232 (Ground)

Thats it ! Simple aint it !

The max232 level converter chip normally runs on 5 VDC but is quite happy with the 3.3 vdc cmos levels.

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2008-06-28 01:17
    The MAX232 is not designed for use at 3.3V. Better would be to use an equivalent chip that's designed for that use, the MAX3232.· This has the same pinout and uses 0.1uF capacitors for the charge pump.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2008-07-01 14:25
    This project still needs some editing and corrections to the data so we’ll move this to the Propeller Forum for now. I would look into what Mike says…The MAX3232 is the 3.3V version of the MAX232. A more clear connection diagram or schematic would also help clarify your connections.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
  • Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
    edited 2008-07-01 15:14
    I'm kinda curious why "10 uf Electrolytic Caps" were used
    for the "charge-pump" connections on the Max232?

    I would have figured something like .1uf ceramic would have been used there.

    Good post, needs a good diagram.

    OBC

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    New to the Propeller?

    Getting started with the Protoboard? - Propeller Cookbook 1.4
    Updates to the Cookbook are now posted to: Propeller.warrantyvoid.us
    Got an SD card? - PropDOS
    Need a part? Got spare electronics? - The Electronics Exchange
  • LeonLeon Posts: 7,620
    edited 2008-07-01 16:23
    I've designed and made a little PCB with a similar circuit on it. It's got its own LDO 3.3V regulator on it to make it more versatile.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle

    Post Edited (Leon) : 7/1/2008 4:31:35 PM GMT
  • parts-man73parts-man73 Posts: 830
    edited 2008-07-01 17:28
    OBC said...
    I'm kinda curious why "10 uf Electrolytic Caps" were used
    for the "charge-pump" connections on the Max232?

    I would have figured something like .1uf ceramic would have been used there.

    The MAX232 does require 10uF "monsters" - the MAX3232 on the other hand specifies .01 uf

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Brian

    uController.com - home of SpinStudio - the modular Development system for the Propeller

    PropNIC - Add ethernet ability to your Propeller! PropJoy - Plug in a joystick and play some games!

    SD card Adapter - mass storage for the masses Audio/Video adapter add composite video and sound to your Proto Board
  • parts-man73parts-man73 Posts: 830
    edited 2008-07-01 17:31
    @ Praxis - Your Schematics are wonderful... might I ask, do you have a certain program to draw those? or do you do them "freehand" ?

    By freehand...I mean with a non-function specific computer drawing program

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Brian

    uController.com - home of SpinStudio - the modular Development system for the Propeller

    PropNIC - Add ethernet ability to your Propeller! PropJoy - Plug in a joystick and play some games!

    SD card Adapter - mass storage for the masses Audio/Video adapter add composite video and sound to your Proto Board
  • PraxisPraxis Posts: 333
    edited 2008-07-01 17:47
    Hi parts-man73,

    I used schematic drafting software to do the circuit.

    Praxis
  • MioTheGreatMioTheGreat Posts: 9
    edited 2008-07-01 17:57
    That schematic doesn't include a hookup for the reset pin.
  • PraxisPraxis Posts: 333
    edited 2008-07-01 18:17
    Circuit Updated.
    MAX3232.png
    1161 x 682 - 37K
  • LeonLeon Posts: 7,620
    edited 2008-07-01 18:27
    parts-man73 said...
    OBC said...
    I'm kinda curious why "10 uf Electrolytic Caps" were used
    for the "charge-pump" connections on the Max232?

    I would have figured something like .1uf ceramic would have been used there.

    The MAX232 does require 10uF "monsters" - the MAX3232 on the other hand specifies .01 uf

    100 nF (0.1 uF) actually!

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle
  • MioTheGreatMioTheGreat Posts: 9
    edited 2008-07-01 19:24
    Praxis said...
    Circuit Updated.

    Beautiful. Thanks.
  • parts-man73parts-man73 Posts: 830
    edited 2008-07-01 20:14
    Leon said...
    100 nF (0.1 uF) actually!

    opps, good catch.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Brian

    uController.com - home of SpinStudio - the modular Development system for the Propeller

    PropNIC - Add ethernet ability to your Propeller! PropJoy - Plug in a joystick and play some games!

    SD card Adapter - mass storage for the masses Audio/Video adapter add composite video and sound to your Proto Board
  • parts-man73parts-man73 Posts: 830
    edited 2008-07-02 02:26
    I've been thinking about the earlier posts in this thread....and I'm now thinking there are more unsolved problems.....

    First of all, I believe in the serial (vs USB) type of interface. P30 should be pulled high. A resistor value of around 4.7k to 10k should suffice.

    Second. Here's an excerpt from a thread I participated in back from 2006. It describes the requirements for the DTR signal.
    Parts-man73 said...
    A question about making a serial port programming adapter. Would it be possible to use a MAX3232 chip instead of the transister network called for in the diagram refered to many times in this forum? This chip is functionally the same as the MAX232, it converts serial port level signals to TTL level signals. The "3232" version of the IC can be run at 3.3 volts.

    One other related questions. Is the serial data Rx/Tx (P30,P31) inverted or non-inverted?

    Thank you,
    Brian

    and the reply from Chip....
    Chip Gracey said...
    That chip should work fine.

    The logic levels are TRUE, not inverted like the signals on the DB9.

    You must make the low-pulse generator for positively-transitioning DTR. To do this, take the DTR signal from the MAX chip and couple it to the base of an NPN via a 10nf cap. Tie the NPN base via a 10k resistor to ground. Tie the NPN emitter directly to ground. The NPN collector must connect to the RESn pin on the Propeller chip. This way, when DTR goes from low to high, RESn will be pulsed low briefly to generate a reset.

    Hope that helps!

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Brian

    uController.com - home of SpinStudio - the modular Development system for the Propeller

    PropNIC - Add ethernet ability to your Propeller! PropJoy - Plug in a joystick and play some games!

    SD card Adapter - mass storage for the masses Audio/Video adapter add composite video and sound to your Proto Board
Sign In or Register to comment.