Author Topic: Weird I²C Signals, or what is it?  (Read 1552 times)

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Offline 128erTopic starter

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Weird I²C Signals, or what is it?
« on: April 05, 2014, 02:43:14 pm »
Hi,
at the moment im probing some data from a ultrasonic level sensor. You can attach a control interface with LCD to it. It uses I²C between the two units (the manufacturer labled it as I²C). In the past i have probed some I²C lines, but this example is a bit weird. In the pictures you can see some analog-like artefacts. To hack into the signals, im using 8cm long wires for SCL, SDA and GND, which i have soldered onto LCD Unit. I can not imagine that it has any effects on the signal integrity (seen from my experiences in the past)

I dont know whats going on there  ;D

By the way: The devices are fully functional and do what they have to do
 

Offline amyk

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Re: Weird I²C Signals, or what is it?
« Reply #1 on: April 05, 2014, 02:59:32 pm »
Pullup resistors charging up the line capacitance. I2C is open-drain.
 

Offline T3sl4co1l

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Re: Weird I²C Signals, or what is it?
« Reply #2 on: April 05, 2014, 04:45:57 pm »
That accounts for the rising edge of most, but what about the reeeeeaaaaaaalllly long edges sometimes seen?

Agree, it's very strange.  Maybe there are interface drivers in there, not just passive pullups?

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
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