Need help wiring Serial device to arduino

Hi I have a 9DOF Razor IMU which spits out sensor data in a serial stream. It runs on 3.3V
Normally it is hooked into an FTDI breakout board and a USB cable from there to a pc.

Because it doesnt have any extra I/O pins and I need to add data from two additional sensors, I need to connect it to an arduino that will simply collect the serial data, collect additional sensor data from its own input pins, then merge them into the stream and send that out USB to processing on my PC.

I am concerned about how to connect the IMU board to the arduino. The Razor IMU has the following pins:


I need to use software serial for this so I figure I can get 3.3v from the arduino, GND as well and hook Tx and Rx to the pins designated for softserial in the sketch.

My question is can I plug rx and tx into arduino pins if the arduino board is 5V and the IMU is 3.3v as long as I feed the IMU only 3.3v to the 3.3v pin???.. and leave CTS and DTR unplugged?

In other words is this correct?


GND ---------> GND
CTS ---------> nothing
3.3V ---------> 3.3V ( or nothing???)
RxI ---------> Tx pin (pin 10 soft serial)
TxO ---------> Rx pin (pin 11 soft serial)
DTR ---------> nothing

OH and do I need to hook up the 3.3v pin at all??? The IMU has its own 3.3v input to run its internal microprocessor and sensors. I think at the serial pins, the 3.3v is an output voltage not input so maybe I just need to do a common ground and not connect the 3.3v to anything…but really not sure
Hope someone can help

If you take a look at the schematics of the Razor, you'll find that the RX/TX are already crossed internally, so you can connect TX to TX and RX to RX to get the desired result. The DTR pin is used only if you wanna reprogram the internal Arduino chip (it's the reset line then). CTS is connected to GND anyway so you don't have to connect it.

Thanks pylon! What about the voltages? Do I connect the 3.3v pin to arduino a 3.3v out? And do the arduino pins put out 5v for Rx/Rx ? And if so will the Razors 3.3v requirements cause a problem when hooking up Rx/Rx pins?

Do I connect the 3.3v pin to arduino a 3.3v out?


To protect the RX of the Razor I would try with a voltage divider (, usually this is enough to protect the 3V3 circuit from damage.