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Hello,

I was wondering if anyone might be able to suggest some ideas for 2 problems I am experiencing.

I'm using an I2C temperature sensor (LM92) with the xmc4500 relax kit.

Problem 1)
I have a problem that after about 5 minutes the clock signal disappears. (I have it connected to an oscilloscope)

Problem 2)
I also have a problem when I use a wire longer than a few cm to connect the temperature sensor. The problem is:
I get no clock signal when I use a 50cm shielded cat 5 network cable for the sensor connection. I tried lowering the bit rate to 100 kbaud but this didnt work.

I appreciate any suggestions people may have.

Thanks

Charles
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Travis
Employee
Employee
First solution authored Welcome! 500 replies posted
Problem 1)
I have a problem that after about 5 minutes the clock signal disappears. (I have it connected to an oscilloscope)

Travis: Clock pulse will be generated only on the transmission side. Can you check if you have stop transmission?
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I have male pin headers soldered to the Relax kit, and that's where I'm directly attaching the oscilloscope probe.

Is that's what you mean?

I do note that there is no clock signal if I disconnect the sensor. Is this normal? It makes it seem like the clock signal comes from the sensor.

I have the CLK signal on pin 0.11 and the data on pin 2.14.

Thanks

Charles
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I have discovered that I was inadvertently causing the clock drop out by connecting the oscilloscope with only one attachment (no ground reference prob)
I dont understand how this caused the clock signal to drop out, but it did!

Now I still have the problem of using a long wire.
The sensor does not work over a 80 cm long shielded wire, UNLESS (and here's the weird part) the oscilloscope is connected to the clock and ground.
It no like the oscilloscope is a life support system!

I noted that in the XMC4500 datasheet The maximum capacitive load for each bus line is 400 pF.
A quick calculation suggests between the wires on my cat5 cable there should be approx 60-100pF so I thought it would be ok.

Maybe I need a bus driver?
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Update for anyone interested;
I tried a bus driver, it didnt work. Couldnt get any signal through it, except a test signal.
So I am now using SMT160 temperature sensor. It is much easier to use!
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