Serial Problem

How can i connect another device with a RS232, 9600 Baud, to Hardware serial port of Arduino UNO?. i used hyper terminal and the device i want to use with arduino works fine, but i cannot read any thing from it using Arduino? The device has a female serial port connector, so far i just connected common ground and hooked up TX of device with pin 2 or Arduino uno (using softwareserial example sketch) but no luck. then i also tried connecting TX of device with RX of Arduino UNO. Please help me fix this problem!!!

You need a RS232 to TTL level converter. You can use a crap design or you can do it right with a chip like a MAX202.

MAX202

That should be "MAX232" I believe. (or HIN232, ADM232, etc)

OP: DO NOT CROSS POST the same question in three different parts of the forum.
It wastes time.

The duplicates have been deleted.

That should be “MAX232” I believe.

No the MAX202 is a perfectly good chip, I use it all the time.

ok thats fine, as far as i know, the max232 is like a voltage converter that helps establish common logic levels? in that case how do i hook up max232 with arduino? i know the chip has rin and rout and tin and tout pins and which direction should it be when connecting it to the arduino? and should i use arduinos hardware RX/TX? many thanks

http://hacking.majenko.co.uk/rs-232-shield

Is the handshaking necessary? I will try this out any ways, thanks

No, it's optional.

Is the handshaking necessary?

No, it’s optional.

Well it is optional at the arduino end but it might be needed at the other end, what ever that is.

You can use a crap design or you can do it right with a chip like a MAX202.

By crap design, do you mean something like this? http://www.sparkfun.com/products/133 I hope not, because I just ordered two!

Quick question, once i connect the MAX232 chip (available to me) to arduino, do i have to disconnect the USB cable which i use to upload the sketch to the board? i would use it to also view the serial data i read from the other device [the other device is an RFID receiver http://www.ebay.com/itm/RF8315R-Active-RFID-Receiver-Module-/300033606407 ]. Thanks

i now built a max232 circuit, now i am receiving something but its just some unwanted character, and not what i am expecting. The baud rate is fine 9600 on every thing (rfid device and uno). My rfid has 2 transmitters and the receiver outputs codes of the transmitters via serial port and should be something like sh001 or sh007 but i am getting only one character for both which is "!". I rebuilt the max232 circuit and now i am getting the same problem but the character is different its "à". I am really annoyed by this small problem to which i have no solution... please help

Do you have an oscilloscope?

Unfortunately not, the thing is serial data is being received at correct time I know this because the RFID receiver upon catching the RFID transmitter, transmits that transmitters serial code out on the serial port every second, and those weird characters come every second. What I am confused about is that is it possible that the onboard arduino UNO serial to USB chip is interfering with data being received from the max232 chip that is sitting between the RFID receiver and the arduino UNO.

By crap design, do you mean something like this?

Yes that is quite a crap design. There is no negative voltage generator. It won't work with a real RS232 interface but will probbly work with the crap ones you get on PCs.

is it possible that the onboard arduino UNO serial to USB chip is interfering with data being received from the max232 chip that is sitting between the RFID receiver and the arduino UNO.

Not likely if the USB is not receiving anything. There is a 1K series resistor between the arduino and the USB chip so a direct connection from a MAX232 will be able to over ride it. However the fact that you have built it twice and got different results suggest you are not building it right. Also as well as the baud rate have you checked the parity?

By crap design, do you mean something like this? Yes that is quite a crap design. There is no negative voltage generator. It won't work with a real RS232 interface but will probbly work with the crap ones you get on PCs.

Crap! Thanks for the tip, Grumpy_Mike. I am reading the output from a digital scale using an RS232 shield from CuteDigi. This shield works great and also allows me to send commands to the scale (like tare, print, etc.), but I can't upload programs while the shield is installed. Another crap design? Now that I've mastered discovered SoftwareSerial, I want to replace the shield with a simple adapter. Do you think what I ordered will work? I guess I'll find out soon enough...