connecttion between inertial sensor (ADI 16450) with usb-8451

[cuem2k]

Does anyone has the same problem? When i connected inerital sensor using SPI (Serial Peripheral Interface) digital

communication protocol in usb-8451, some first days it were working pretty well, then it has problem sending out wrong data.

However, when i hooked the ocsiloscope to any of the SDI or SDO to measure the signals, it works fine again.

Any of you have face the same problem, please let me know what happen? 

[Albert.Geven]

Seems to be something with signal integrety.

How long is your cable and which voltages do you measure with your scope.

[cuem2k]

The cables are not so long, it is about 2-3 feet. The signals on the acsiloscope are the stream of pulse from 0-3.3 V that are the same with the spec of sensor. Do you think is these any wrong with the A/D and D/A in the USB device?

[Albert.Geven]

Hi

I don't think something is wrong with AD or DA but maybe with powersupply or signal integrity on the wires.

picking up interferences and repairing this by connecting a probe reminds me of a computersetup one of our customers had in 1982!

The system only worked when the scope was connected.

It happened that a powersupply did reach the correct voltage almost. Other system I have seen since show behaviour like that when the connecting cables are not twisted with ground or when ground is completely absent.

So check your complete system carefully.

[cuem2k]

Thanks for your reply!

I did try different powersupplis orther than the +5V from the the USB device but it still had the same problem. As you said I think

that ground is causing problem. Let's me check it again.

[cuem2k]

I double checked my system today, it still has the same problem, although i tried a different powersupply and ground. Powersupply is 4.92, it is in the range of sensor requirement Vcc=4.75 - 5.25 V. I could not figure out what happen with them. Every time i unhook the probe, i have to disconnect the USB with computer and then connects it again ortherwise the sensor send out the wrong data.  

[Justin_E]

I'm assuming the USB-8451 is connected to your PC. When you say you've tried a different powersupply, are you saying you've swapped out the PC's supply? Have you tried the USB device in a different USB port? Are you using a USB hub or anything like that?

Like Albert said, it seems like there's an issue with the signal integrity. Can you try reducing the wire lengths between the screw terminals on the USB device and where they're connected to? What kind of environment is this device in?

[cuem2k]

I did try everything from switching to different USB ports to using powersupply in the PCIe card. It still did work. It was very

interesting that when i holded the output signal wire and ground wire in my fingers, it worked fine. Thus, i think i should add a

resistor between these wires to drop the current on the output signal. Please let me know if you have any suggestion.