I’m working on a project using I2C with an Arduino Nano, and I’m having trouble with the signal integrity when running long cable, around 8-10 feet. I saw the [BOB-14589, an I2C Differential Breakout using the PCA9615, and it looks it might be what I’m looking for with its limitation being 100 ft. However, I have some questions regarding it.
First off, the Quicc connectors are there just for Quicc devices, correct? From what I see in the schematic, there’s no real circuitry to limit it to Quicc devices, so with the 5-pin header at the end, it can be used with any I2C sensor (non-Quicc), correct? If that’s the case, what is the purpose of the EN pin?
Second, I’m confused as to the methods of powering the board. For my application, the sensor will be receiving +5V power through the I2C connector and not through an external separate power supply due to space. Therefore, it seems that using the VDD_B and GND pin next to it is not necessary in my case. Reading the get-started guide, it looks like what I need to do is shown in the ‘VDD_A == VDD_ B, Power Whole Bus (Non-Qwiic Option)’ section, but what exactly do I have to do in order to get this configuration? I’m only using one I2C sensor at each connector, so I don’t need to power multiple devices.](SparkFun QwiicBus - EndPoint - COM-16988 - SparkFun Electronics)
First off, the 5 pin header is ‘seperate’ the Qwiic connector. They share some pins but won’t interfere with each other. ‘EN’ is for enable. From the [product hookup guide:
“EN (optional) - PCA9615 enable (active high, internally pulled up). This is used to disable the bus buffer, and is useful for fault finding, power-up sequencing, or reconfiguration of a large bus system by isolating sections not needed at all times.”
The key note for VDDA - VDDB is using 5V AND 3.3V. Keeping it shorted will allow you to work with 5V to 5V or 3.3V to 3.3V.
Thank you for your reply. Based on what you said, I just have to keep it shorted. Since VDDA and VDDB are both shorted together already, there is no need to make any modifications to the breakout board to power the I2C module through RJ-45 (and not from an external power source), correct?
TS-Brandon:
First off, the 5 pin header is ‘seperate’ the Qwiic connector. They share some pins but won’t interfere with each other. ‘EN’ is for enable. From the [product hookup guide:
“EN (optional) - PCA9615 enable (active high, internally pulled up). This is used to disable the bus buffer, and is useful for fault finding, power-up sequencing, or reconfiguration of a large bus system by isolating sections not needed at all times.”
The key note for VDDA - VDDB is using 5V AND 3.3V. Keeping it shorted will allow you to work with 5V to 5V or 3.3V to 3.3V.
I hope this helps!
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Brandon,
Thank you for your reply. I apologize, but there was one other thing that I wanted to ask you. The PCA9615 IC that you use on the breakout board converts the I2C signals to a differential pair of signals. Add that and power and ground for a total of six signals which goes to the RJ-45 connector. Theoretically, if I were to replace the RJ-45 connector with another type of connector (something smaller, more compact), as long as it has six pins, any connector can really work in place of the RJ-45 connector over long distances?](https://learn.sparkfun.com/tutorials/qwiic-differential-i2c-bus-extender-pca9615-hookup-guide?_ga=2.176836261.1003182432.1578944325-2114068872.1578439588#hardware-overview)
The connector itself, while engineered to handle specific operating conditions, has very little to do with the signals themselves. You can fully remove the connector and replace it with corresponding wires. I would advise that, whatever your replacement is, use shielded wires to help protect the integrity of the signal over long distances.
TS-Brandon:
The connector itself, while engineered to handle specific operating conditions, has very little to do with the signals themselves. You can fully remove the connector and replace it with corresponding wires. I would advise that, whatever your replacement is, use shielded wires to help protect the integrity of the signal over long distances.
Thank you for your reply. I apologize, but I have one final question about the breakout board. I was wondering why you chose 4.7k ohms for your pull-up resistors on the SCL/SDA lines of the IC. I’m trying to calculate the minimum pull-up resistor value based on the value for the low level output voltage, but the low-level output current conditions make it hard to pin down what the minimum would be for the IC.
That’s ultimately a decision by the engineer who designed it. 1k, 2.2k, 4.7k, and 10k are some common values you see used as pull-ups. Usually, datasheets will give recommended values for pull-up resistors. Try checking the [Datasheet to see if it gives a recommendation for a pull-up resistor for your purposes.](https://cdn.sparkfun.com/assets/a/5/1/3/6/PCA9615.pdf)