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Help trouble shooting MAX232 interface

Started by Sal P. February 10, 2007
I'm attempting to interface a CMOS camera module [C328-7640] to my PC
via the RS232 com1 port to learn how to interface with the chip.

The modem cable is working ( I tested it by connecting the Tx & Rx
pins (2& 3) then opened hyperterminal and when I type any letters they
get written on the terminal )

I put both the schematic and how the breadboard is wired on my website
to show what I did:

http://www.polifemo.us/mambo/index.php?option=com_content&task=view&id=25&Itemid=41


The power comes from a 5V / 750ma Blackberry charger, and I use the
resistors shown on the left of the breadboard to provide 3.3 volts to
the upper rails.  The voltage is 5V to the bottom rails and 3.3V to
the upper rails and I can see that with a voltmeter.

The one thing I'm not sure is if the capacitors are polarized as I
dont see any markings on them, I'm using Digi-Key # BC1148CT-ND
[ 0.10uF 25V ceramic +80/-20% ]

It is my understanding that I should be able to issue control codes in
hyperterminal and see a reply from the C238 module, assuming I got the
baud rate correct.

Thanks for the help in troubleshooting this.

Sal

Sal P. wrote:


> The modem cable is working ( I tested it by connecting the Tx & Rx > pins (2& 3) then opened hyperterminal and when I type any letters they > get written on the terminal )
I'd suggest disconnecting your camera module and connecting pin 11 to 12 on the max232 for a local loopback test.
> The power comes from a 5V / 750ma Blackberry charger, and I use the > resistors shown on the left of the breadboard to provide 3.3 volts to > the upper rails. The voltage is 5V to the bottom rails and 3.3V to > the upper rails and I can see that with a voltmeter. >
I'd suggest providing a properly filtered and regulated 3.3v supply for the module; a bare series dropping resistor most likely won't do. Regards, Michael
On Feb 10, 3:03 pm, msg <msg@_cybertheque.org_> wrote:
> Sal P. wrote: > > The modem cable is working ( I tested it by connecting the Tx & Rx > > pins (2& 3) then opened hyperterminal and when I type any letters they > > get written on the terminal ) > > I'd suggest disconnecting your camera module and connecting pin 11 to > 12 on the max232 for a local loopback test. > > > The power comes from a 5V / 750ma Blackberry charger, and I use the > > resistors shown on the left of the breadboard to provide 3.3 volts to > > the upper rails. The voltage is 5V to the bottom rails and 3.3V to > > the upper rails and I can see that with a voltmeter. > > I'd suggest providing a properly filtered and regulated 3.3v supply > for the module; a bare series dropping resistor most likely won't do. > > Regards, > > Michael
thanks Michael I will try it. It did not occur to me to test across the MAX232 chip the same way I tested the cable. Sal
Sal P. wrote:


 > I put both the schematic and how the breadboard is wired on my website
 > to show what I did:
 >
 > 
http://www.polifemo.us/mambo/index.php?option=com_content&task=view&id=25&Itemid=41
 >

Also check your schematic; you've drawn a zero-volt power connection to
your camera module.

Regards,

Michael
On Feb 10, 3:13 pm, msg <msg@_cybertheque.org_> wrote:
> Sal P. wrote: > > > I put both the schematic and how the breadboard is wired on my website > > to show what I did: > > > >http://www.polifemo.us/mambo/index.php?option=com_content&task=view&i... > > > > Also check your schematic; you've drawn a zero-volt power connection to > your camera module. > > Regards, > > Michael
I tested putting a loop back on the TTL side of the MAX232 chip and the characters got echoed back, so it seems the problem is with the CMOS camera module. I will try to put a proper 3.3V power supply and try again. Thanks for the help. Sal