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Author Topic: UNO board I2C pullups? Can be enabled/disabled?  (Read 2342 times)
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The scanner sketch miss-reports the device address.
No it doesn't it reports the address you must use in an Arduino environment, this like many other implementations of the bus do not include the R/W bit as part of the address. 
It is difficult to tell much from the photos as they are too blurred.

Were those traces from your code? The data does not look to match what you have posted as your code.

Things to try:-
The code on the module's web site.

A different I2C library
http://dsscircuits.com/articles/arduino-i2c-master-library.html

It could be you have a faulty module.
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It is difficult to tell much from the photos as they are too blurred.
Can't do better, I'm afraid.

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Were those traces from your code? The data does not look to match what you have posted as your code.
The traces were from the I2CScanner code. As you can tell from the code, the program puts out many addresses. The scope is triggering on the SDA trace (blue), but it could be for any address.

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Things to try:-
The code on the module's web site.
Did that some time back.

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I'll try it.

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It could be you have a faulty module.
I think that's the problem. When I first used the module, it worked fine. Then I put an 8 ohm speaker on the output. I read the manual later and it implies that the output should not be loaded at all - even the scope probe had to great an input capacity (some 100 pf). Since then its been misbehaving. But I didn't think the I2C system would be damaged.
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Then I put an 8 ohm speaker on the output.
Yep that would screw it.

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But I didn't think the I2C system would be damaged.
Well you never know what is going to be damaged because you don't know how the die is laid out.
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Well you never know what is going to be damaged because you don't know how the die is laid out.
. Yet the chip has a 10 ohm resistor at the output, and the manual's cautionary note was for good waveforms at high frequency ... but after trying the decoupling, I can think of no other reason.
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Just as a follow up:
I obtained a few samples of the LTC6904 chip and wired one up to the UNO in the same way as the module was. The changes in frequency are more reliable than with the 1st chip, but that reliability goes down with the greater frequency coming out of the chip. Changes in low frequency, say in the range of 200 KHz appear the work just fine; in the range of 60 MHz, the change attempts often cause I2C errors.

In addition, the new chip seems to have a much higher frequency jitter at its output than for the 1st chip.

I think I'm going to look for another, more reliable, chip than the LTC6904. Its a bit of a nuisance.

Thanks.
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in the range of 200 KHz appear the work just fine; in the range of 60 MHz, the change attempts often cause I2C errors.

I would definitely say that was a decoupling issue with your layout. Read this:-
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

That is a high frequency you are dealing with and it can get into the supplies. I would also include a 1nF ceramic decoupling capacitor as well as the normal ones.
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in the range of 200 KHz appear the work just fine; in the range of 60 MHz, the change attempts often cause I2C errors.

I would definitely say that was a decoupling issue with your layout. Read this:-
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

That is a high frequency you are dealing with and it can get into the supplies. I would also include a 1nF ceramic decoupling capacitor as well as the normal ones.
If you recall (reread some of your posts), we tried both large and small caps at the same time. There was no difference. However, I do believe you and I did read the article on decoupling (there are better descriptions). Unfortunately, I have had to put the project away for now. Perhaps in a few weeks we can try something more.
Sorry, but thanks for your help.
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