Need help troubleshooting 3.3v SPI

Forum 2005-2010 (read only) Hardware Interfacing
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Hi everyone? I'm having trouble interfacing with a LIS3LV02DQ 3-axis accelerometer via SPI. I am using the breakout board from Sparkfun which sadly has been discontinued (the schematic for the breakout board is located here: http://www.sparkfun.com/datasheets/Sensors/LIS3LV02DQ-Breakout.pdf)

and here is the datasheet link:

http://www.st.com/stonline/products/literature/ds/11115/lis3lv02dq.pdf

This is a 3.3v device but there have been many successful attempts to interface via I2C or SPI at 5v (references below)

http://www.nearfuturelaboratory.com/2006/09/22/arduino-and-the-lis3lv02dq-triple-axis-accelerometer/

http://interactive.usc.edu/members/jbleecker/archives/006915.html

http://www.kerrywong.com/2010/04/17/interfacing-lis3lv02dl-using-spi-ii/

I have indeed been successful at interfacing with this at 5v (good “WHO_AM_I” value of 0x3A and clearly good data, but so far have been unsuccessful using 3.3v (“WHO_AM_I” of 0xFF or sometimes 0x3F and bad data). I have tried using the 3.3v output from the arduino as well as using a voltage divider on the 5v output, bringing it down to 3.4v or so? neither worked (with nothing else changed from the wiring that worked when I ran the 5v output directly to power the breakoutboard).

I have also tried using the inline resistor method covered at sparkfun (http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=65) to interface between the 5v arduino and 3.3v accelometer without success. It is worth noting that this same circuit worked perfectly for me when interfacing with a 3.3v SCP1000 pressure sensor breakout board. I pulled that board out and popped the accelerometer into the same circuit but no worky.

There are no _CS conflicts on the bus (the accelerometer is currently the only sensor on the bus)

Can anyone explain why I can interface fine at 5.0v but not at 3.3v (as it was designed for?!)

Any suggestions on further troubleshooting? I really want to get this working at 3.3v as I plan on additional 3.3v sensors on the SPI bus that are not as overvolt tolerant as the LIS3LV02DQ apparently is. If this can't be solved, can anyone suggest a safe way to interface with both 3.3v and 5.0v sensors on the same SPI bus?

Unfortunately I do not have a logic analyzer? (if anyone can recommend a cheap one I would appreciate it!)

Thanks in advance

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Any chance you can sketch out your circuit?

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You can use a hex converter, Sparkfun has one on their micro sd shield.SparkFun microSD Shield - DEV-12761 - SparkFun Electronics

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I'll try to upload a schematic tonight. I'll certainly consider a hex converter and I have a sparkfun logic level shifter I could try. That aside, I'm still interested in finding out why my existing circuit won't work. I have very little electronics background but having reviewed the forums, I'm wondering if this could be an impedance issue or if perhaps the capacitance of my breadboard is a factor (I'm using a breadboard for the voltage divider circuit as well as the inline resistors - the successful 5v supplied circuit did not use the breadboard... I just directly wired the accelerometer's pins to the relevant arduino pins).