SparkFun Forums

[bretskee]

OK, so here goes my dumb question. First of all, I do not pretend to understand how the rs232 shifter circuit works and I think I have overcome the dislexia extensively described in relation to this product. My plan is to use two of these devices back to back to extend an otherwise TTL serial connection over a few metres between a 407 GPS with arducopter interface card and a fez domino / arduino.

First I thought I would get one unit working using a USB FTDI inteface card to go USB to TTL and then put this into the the rs232 shifter TTL input and loop back on the rs232 side so that I could see characters echo on a terminal program. I used volts from the FTDI card to power the RS232 shifter. The FTDI card provides both 3.3 and 5 volts. After getting the ins and outs correct using 3.3v power all is good and I see the characters echoed as expected and LEDS blink as they should. When I went to use 5v, I get an odd problem. Both LEDS on the shifter card light (one brighter than the other) and my loopback no longer works. This is repeatable with the other shifter I have and restoring the 3.3v return all to the working condition so I assume I have not fried anything.

Can anyone tell me what is going on. Is there some issue with the TTL interfaces being 3.3v (but 5v tollerant) and powering the shifter with 5 volts. I am totally stumped.

[Cannibal]

The only time I used the shifter, I had some issues and decided to just use ds323's and the like in the future.

My guess is that the output low voltage of the shifter is too high and reads as a 1 by the processor even when it's supposed to be a zero. You could try resistively loading your RX line to see if that helps bring it back into the valid range, but rather than worry about this type of matching, I suggest just grabbing one of the IC's that does this job.