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MAX233A TTL RS232 Conveter with LK204-25 and Basic Stamp
Posted: Thu Apr 16, 2009 9:02 pm
by ronczap
Has anyone tried using a MAXIM MAX233A converter IC to connect a Basic Stamp 2 to a LK204-25 using the DSUB serial port?
I would like to leave the protocol jumpers set for RS232 so I can connect the LCD to the computer serial port sometimes and also be able to use it with a Basic Stamp via the MAX233A converter.
Unfortunately, it appears that the LK204-25 does not respond to the signals from the MAX233A. Maybe the converters output voltage is too low.
Any suggestions?
Posted: Fri Apr 17, 2009 11:20 am
by Raquel
Hi,
Thank you for posting on the forum.
The MAX233A looks like a standard RS232 driver, so it should work,
You might want to double check your connections from Basic Stamp and then the connections to the display. Swapped TX and RX is normally overlooked and connected incorrectly, so you want to make sure those are correct.
Best Regards,
Posted: Fri Apr 17, 2009 12:36 pm
by ronczap
Raquel,
I have the MAX233A wired on a small PCB using both RS232/TTL pairs - one with a male connector and the other with a female. They are wired the same and I can connect thru my computer's serial port with no problem.
Despite that, I tried switching the TX and RX wires (per your suggestion) between pins 2 and 3, but the LK204-25 still does not interface.
BTW - I set LCD to remember the 9600 baud rate and the Basic Stamp baudmode to 84 (the BS2 setting for 9600,n,8,1).
I tried some other BS2 baudmode settings to no avail.
Not sure what to try next.
Thanks for your suggestion though.
Posted: Fri Apr 17, 2009 2:55 pm
by Raquel
If I understand you right, the Basic Stamp with MAX233A converter connects to the PC no problem? How about the display? Does the display connect to the PC no problem?
If it does, then what I suggest is to get a null modem cable to connect Basic Stamp (plus MAX233A) to the LK204-25 display. Or, if you do not need to connect the Basic Stamp to the PC, you can use a straight through cable and permanently switch the TX and RX (such that DB9 pin 2 is RX pin of the MAX233A and DB9 pin 3 is TX of the MAX233A), leave the TX and RX of the LK204-25 display as is.
Also, you probably have GND connected, but just want to mention it here. You should have pins 2,3 and 5 (GND) connected of the DB9 connector.
I hope this helps.
Posted: Sat Apr 18, 2009 5:03 pm
by ronczap
Raquel,
I have it working now. I thought I had swapped the TX/RX DB9 pins coming out of the MAX233A but didn't.
I tried it again and everything works perfectly...
It should be like this:
LK204-25__________________ MAX233A___________ Basic Stamp
--------------------------------RS232 || TTL --------------------------
DB9 pin 3 (TX) <-- pin 18 (T2out) || pin 1 (T2in) <-- Serout
DB9 pin 2 (RX) --> pin 19 (R2in) ..||. pin 20 (R2out) --> Serin
NOT THIS
LK204-25__________________ MAX233A___________ Basic Stamp
--------------------------------RS232 || TTL --------------------------
DB9 pin 2 (RX) <-- pin 18 (T2out) || pin 1 (T2in) <-- Serout
DB9 pin 3 (TX) --> pin 19 (R2in) ..||. pin 20 (R2out) --> Serin
Thanks for your help!!!
This is much better than swapping those protocol jumpers back and forth!
MY SUGGESTION
I wish you would implement plug type jumpers or dip switches instead on the next hardware revision...
- Ron