Help trouble shooting MAX232 interface

Feb 10, 2007 4 Replies
S

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:



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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



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M

I'd suggest disconnecting your camera module and connecting pin 11 to

12 on the max232 for a local loopback test.

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

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S

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

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M

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

Regards,

Michael

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S

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

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