The schematic says DNP (DoNotPopulate):
(cannot upload picture)
But I can see two resistors near SDA and SCL on the board:
(cannot upload picture)
Thank you!
Hi there,
Usually there is a BOM and that would tell you, behind the schematic on the wiki, I see none there,
These two?
They should be left off. but either way,
For most standard I2C communication, both 4.7 kΩ and 10 kΩ resistors should work well. However, there may be instances where calculating exact pull-up resistor values is optimal for system performance, and this depends on factors like speed, capacitance, and the number of devices connected on the bus. so YMMV
HTH
GL 
PJ 
You’ll know when its wrong value because it won’t work very far or fast. 
Hi, they are there apparently from the picture.
Could not find a BOM so I still do not know the values.
I hope someone around here knows the values and can answer this question.
Thanks!
Hi there,
So does your board have them?
What are you trying to achieve , If i may ask?
Have you connected other I2C devices?
GL PJ
Hey, I’m debating if I can use this board with an I2C longer wire (5 feet) that is why I was asking about the values.
If they are 10kOhms, I’m pretty sure this will not work for my scenario.
If they have a lower value, I may have chances (to be tested).
Yes, I’ve been playing with many, mostly connected to Particle devices with this nifty board:
Cheers and thanks
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Hi there,
WOW, 5 Feet that is a long way , what speed?
I see this: The maximum length of an I2C (Inter-Integrated-Circuit) cable depends on the bus speed, and is generally limited to a few meters:
- 100 Kbaud: Maximum length of 1 meter
- 10 Kbaud: Maximum length of 10 meters
- 100kHz clock speed: Rough guideline of 12 inches
- 400kHz clock speed: Rough guideline of 6 inches
- 1MHz clock speed: Rough guideline of 3 inches
Other factors that affect the maximum length of an I2C cable include: Pull up resistors, External interference, Wire quality, and Capacitive loading.
Here are some tips for extending the length of an I2C cable:
- Run at a lower clock frequency
- Use twisted pair and/or shielded cable
- Use an active current source instead of a pull-up resistor
- Use a charge pump to reduce “ghost signals”
- Use USB devices in conjunction with an active USB extension
Solution According to Analog Devices
The maximum distance of an I2C bus depends on the capacitive loading. In typical applications, the length is limited to a few meters in standard mode. This is because a system has to be built to accommodate a maximum bus capacitance of 400pF to meet rise time requirements listed in the I2C bus specification (Rev. 6 – 4 April 2014). To achieve greater distances by operating above the maximum allowable bus capacitance, the I2C bus specification allows operating at a lower speed, using higher drive output devices, dividing the bus into segments with bus buffers, or the use of switched pullup circuits. While on the surface these methods may seem viable, they either do not meet the long-distance requirements or significantly increase the cost. An alternative is to use the DS28E17 1-Wire-to-I2C Master Bridge.
I like it…
check it out over HERE
Sounds like you need can bus or IEEE488 
jk’n…
HTH
GL PJ
hehe, imagine if I could use that 
There’s this other document from TI that I read when I need to do calculations:
So, if I start with:
- 10pF for each i2c device, 10pF for the micro controller and 10pF stray capacitance plus 50pF per meter of CAT5 cable (x2 for 2 meters)
That translates to: 130pF
I go with that value to the doc above, and the min and max values for resistors are:
Standard mode (100kHz) : between 967 Ω and 6.5 kΩ.
Fast mode (400kHz): between 967 Ω and 1.96 kΩ
So the standard mode (100kHz) allows me to use standard 4k7Ω resistors for pull ups on a 2 meter wire IF the premise of the wire having 50pF is real.
What do you think, do I still need to look into IEEE488?
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I think you got it no problem.
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