P82B715 question.

Projects Networking, Protocols, and Devices
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I'm considering using the P82B715 to extend a I2C bus. I planned to have three wires, SDA, SCL and GND.

But when looking at this page I see that they use 4 wires, SDA, SCL, GND and Vcc.

I assume that Vcc is not required if the equipment at the other end has it's own power supply? Or is it required? I could not find anything about this in the datasheet.

If there are someone here that has experience with the P82B715 I would appreciate to get some feedback on how long they have extended the I2C bus.

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I assume that Vcc is not required if the equipment at the other end has it's own power supply? Or is it required? I could not find anything about this in the datasheet.

It is required to power the chip. If the "other end" drives the chip it might be not be necessary to connect it to the Arduino side but in the end it has to be connected.

If there are someone here that has experience with the P82B715 I would appreciate to get some feedback on how long they have extended the I2C bus.

I have used it to extend the bus to about 2-3 meters.

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pylon:
It is required to power the chip. If the "other end" drives the chip it might be not be necessary to connect it to the Arduino side but in the end it has to be connected.

I have used it to extend the bus to about 2-3 meters.

Both ends have it's own power supply.

I see that very low resistors are recommended for pull-ups on the line between the two chips - as low as 330 Ohm. May I ask what you used?

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I see that very low resistors are recommended for pull-ups on the line between the two chips - as low as 330 Ohm. May I ask what you used?

That depends on your circuit. We use 470Ω pull-ups if I remember correctly but we had a rather high wiring capacitance. Section 8.1.1 of the datasheet shows you how to calculate the resistance you need.

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Thanks.

Guess we have different datasheets since I find the formula R = 1uS / (Cdevice + Cwiring) in a different section.
Assume you are talking about this.

Just have to measure the wire capacitance then :slight_smile:

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Just have to measure the wire capacitance then

And maybe the capacitance of the connected device too.

Guess we have different datasheets since I find the formula R = 1uS / (Cdevice + Cwiring) in a different section.

I used this one.

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pylon:
And maybe the capacitance of the connected device too.

Of cause. Measuring the wire capacitance is easy since my multimeter can do this. But how can the capacitance for devices be measured?

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Of cause. Measuring the wire capacitance is easy since my multimeter can do this. But how can the capacitance for devices be measured?

Usually the datasheet tells you that.

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