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|   March  3, 2009 at 5:26 PM

I just got mine up and running (only it's RX pin for now) and it works great with hyper terminal. I soldered on downward facing header pins and it slots right into my breadboard. THANKS!

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|   March 18, 2009 at 10:22 AM

Before purchasing this part you need to know if you have a condition called UART dyslexia. This is a neurological disorder that will render you incapable of properly wireing this device no matter how my times you triple check the the wiring. I have this disorder and I have only found three possible solutions:

1) Find someone else without UART dyslexia to wire it up for you
2) When you get the board, immediatly scratch out the silk screen for the TX and RX pins. You will have a better chance attaching the wires at random than attemping to determine the proper connections in your screwed up head. Test the device and if it doesn't work swap the lines. The advantage of this approach is that you didn't spend hours trying to figure out the wrong way to wire the connections.
3) Try to figure out the proper connections and do the opposite of what you think is correct. I have had some success with this approach.

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|   April 18, 2009 at 4:18 PM

I am not joking! That has been driving me crazy for months! Why is it so mind boggling to want to add a DB9 male port to my micro controller so that I can use it with the card reader! I think i'm suppowed to add power to pin 2 and 1???

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|   April  7, 2009 at 10:15 AM

As a UART dyslexia suffer, can I can match the TX-O silk to the RX pin of my uC and the RX-I silk to the TX pin of the micro and expect success with a normal serial cable and hypertermal?

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|   April  9, 2009 at 12:01 AM

Are there any plans to make a "Pro Version" that will level-shift all RS232 I/O lines? Interfacing with many industrial devices via RS-232 requires using flow control.

The Intersil ICL3243 IC would work perfectly for this, and provide complete serial port functionality.

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|   October  5, 2009 at 8:39 PM

I second that request! A unit that supports ALL the handshaking lines would be fantastic! At the moment I'm trying to do this with some MAX232s and suffering from the afore-mentioned UART-dyslexia... Having a module to take care of this automagically would be great.

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|   October  5, 2009 at 8:44 PM

Perhaps a Maxim MAX235 would also be suitable? It has the advantage of not requiring external capacitors which should allow smaller, more flexible installations...

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|   April 29, 2009 at 11:11 AM

The I and O on the TX and RX pins refers to those pins, specifically. The RX-I pin, the one on the four-pin header, is an input, and this is connected to pin 2 (RX) on the DE-9 connector. The TX-I pin, the one on the four-pin header, is an output, and this is connected to pin 3 (TX) on the DE-9.

This makes your microcontroller a DCE (modem), as opposed to a DTE (terminal), and as such, you should connect this to a computer (which is a DTE) using a straight-through DE-9 cable, not a null-modem cable.

With regard to level shifting, this board does not have a MAX232 or equivalent, so it does not comply with the classical RS232 spec (0 = Space = +12V, 1 = Mark = -12V). Instead, its input will accept RS232 voltages on the input and shift them (-12V [mark] -> VCC, +12V [space] -> GND). For its output, it merely inverts the signal (VCC->GND, GND->VCC) so you must be using a newer UART that will tolerate this.

I believe this is accurate - if it's not, feel free to correct me.

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|   May 10, 2009 at 9:21 PM

I just got around to using this guy and he works great. RX-I is, indeed, an input to the PCB and TX-O is the output. Simply wire your uC TX to RX-I on this product and your uC RX to TX-O on this product and you are good to go. Thanks for another good product from SFE.

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|   June 12, 2009 at 9:12 AM

MotiveForce: Before purchasing this part you need to know if you have a condition called UART dyslexia. This is a neurological disorder that will render you incapable of properly wireing this device no matter how my times you triple check the the wiring.

Here's a hint that works for me. It's fairly easy to remember that for basic serial comms, the numbers to know are 2, 3 and 5. Two and three are data, five is ground. The problem is always to keep track of which data line is which....and on the corner of whiteboards around the office, I write "PC talks on Three!"

Once you know that, everything else falls into place.

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|   September 18, 2009 at 1:52 PM

I initially started with this device and later transitioned to the BlueSmirf Gold break-out. The great thing is that the pinout on this is mostly pin for pin compatible with the pins on the BlueSmirf. Actually, the BlueSmirf has an extra 2 pins on it with the extra pins being at each end, but that hasn't stopped me from using both interchangeably.

It probably wasn't intentional, but I think it's great that I can choose a wired or wireless connection just by changing out one part!

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|   October 25, 2009 at 8:34 PM

This is only a EIA-232 shifter is it not?

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|   November 26, 2009 at 5:28 PM

Ok help!!!! EE 101 help needed. how in blazes does this thing convert the TTL tx signal to 12V??? If VCC is 5V, I can't see how it creates the 12V from the 5V VCC from the schematic.

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|   January 11, 2010 at 3:10 PM

it might be using a dc-to-dc step up regulator.

something like this: http://www.sparkfun.com/commerce/product_info.php?products_id=8249

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|   December 14, 2009 at 1:55 PM

jleslie48: Ok help!!!! EE 101 help needed. how in blazes does this thing convert the TTL tx signal to 12V??? If VCC is 5V, I can't see how it creates the 12V from the 5V VCC from the schematic.

It doesn't really convert VCC to 12v. It simply pulls the output (pin 2 on the DB9) up to the level of VCC for "mark". To get the lower negative voltage for "space" it uses a clever little trick of stealing and storing the negative voltage from the connected host coming in on pin 3. This is done with the diode D1 and the capacitor C1 (note how the capacitor is installed with the + side connected to ground). This negative level is then just allowed to feed back out pin 2 via R1 to the connected device when not pulled up by Q1 for a "mark". If the connected devices does not supply a negative "space" signal then it probably doesn't require a negative "space" just a voltage level around 0v or below for "space" and above 3v (even as low as 1.5v will work, from my experience) for "mark" as per EIA-232 specification rather than the old RS232 spec of +/- 12v.

BTW. I could be totally wrong on this too.