[AVR] Problem with SHT11 cable

[Sharagim]

Hi,
I have a SHT11 and Xmega64 and have problem with cable and wires.
As you see in attachment if there is some gap between clock(SCK) and other wires (Specialy GND), it is working perfectly but when they are close to each other I am getting error. In the datasheet I see there is some notice about crosstalk but over 10cm.
I tried twisted pair with better result but at the terminal connector if they are close to each other problem exist yet.
SDA and SCK are pulled up.

 

[hobbyckts]

Try using shielded cable. That should solve the problem

 

[bigdogguru]

As you see in attachment if there is some gap between clock(SCK) and other wires (Specialy GND), it is working perfectly but when they are close to each other I am getting error. In the datasheet I see there is some notice about crosstalk but over 10cm.

One possible option is to utilize a flat cable, with every other conductor connected to GND. This technique is utilized in some high speed parallel interfaces, like ATA.

I tried twisted pair with better result but at the terminal connector if they are close to each other problem exist yet.
SDA and SCK are pulled up.

As they are NOT a differential pair, you certainly do NOT want to utilize a twisted pair.


BigDog

 

[Sharagim]

Thx for replies.

One possible option is to utilize a flat cable, with every other conductor connected to GND. This technique is utilized in some high speed parallel interfaces, like ATA.

Could you please confirm if you mean :
|GND|SCK|GND|SDA|GND|VCC

 

[bigdogguru]

Yes, the commonly used ATA HD cables used in PCs have a similar arrangement, quite effectively I might add.

Utilizing a flat cable would also prevent any of the signal lines from inadvertently crossing, while the GND lines offer some protection from EMI from nearby signal lines.

BigDog

 

[Sharagim]

Thx,
I tried to capture with scope and see what is different between the cables and wire positions. but I couldn't find something bold. Do you have anything which can help me on see them on scope?

 

[bigdogguru]

It appears to be a standard I2C synchronous serial interface, if so the serial clock line (SCK) is interfering with the adjacent serial data line (SDA). The I2C protocol was not originally intended for a flying lead implementation, especially relatively long leads.

BigDog