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For Shielded RJ45 connector, is it better to connect SH-1 and SH-2 to ground or ...

suckatpcbb

@copilot Is it ok for me to assume that pin1 and pin2 are the same twisted pair, Pin3 and Pin4 are the same twisted pair, etc?

copilot

It's generally a reasonable assumption that pairs of adjacent pins on RJ-45 connectors correspond to the same twisted pair, particularly when following standard Ethernet wiring schemes such as T568A or T568B. The typically used pinout for Ethernet cables, which would use an RJ-45 connector like the RJHSE-5380, is as follows:

Pair 1: Pins 1 and 2
Pair 2: Pins 3 and 6
Pair 3: Pins 4 and 5
Pair 4: Pins 7 and 8

Based on this standard pinout, your assumption would not always hold true as per the T568A and T568B standards, because the pairs are not simply adjacent pins except for the first pair (Pins 1 and 2). Here's the standard mapping for clarity:

T568A

Pair 1: Pins 4 and 5 (Blue)
Pair 2: Pins 3 and 6 (Green)
Pair 3: Pins 1 and 2 (Orange)
Pair 4: Pins 7 and 8 (Brown)

T568B

Pair 1: Pins 4 and 5 (Blue)
Pair 2: Pins 1 and 2 (Orange)
Pair 3: Pins 3 and 6 (Green)
Pair 4: Pins 7 and 8 (Brown)

If you're following standard wiring, you'll need to check the specific Ethernet wiring scheme you intend to use.

For your project, the assignments for the pins on your RJHSE-5380 are as follows:

J5:1 and J5:2: First twisted pair (usually TX+ and TX-).
J5:3 and J5:5: Second twisted pair (usually RX+ and RX-).
J5:4 and J5:5
J5:7 and J5:8

In summary, Pins 1 and 2 form a pair; Pins 3 and 6 form a pair; Pins 4 and 5 form a pair, and Pins 7 and 8 form a pair.

Always refer to your specific component's datasheet or wiring standard for the most accurate information.

suckatpcbb

@copilot For Shielded RJ45 connector, is it better to connect SH-1 and SH-2 to ground or just one of them is enough?

copilot

For a shielded RJ45 connector like the RJHSE-5380, it is generally recommended to connect the shield pins (SH-1 and SH-2) to ground. The purpose of the shield is to protect against electromagnetic interference (EMI) and ensure proper grounding improves the effectiveness of the shielding. Here’s a breakdown of the connections:

Connect both SH-1 and SH-2 to ground: This ensures that the shield is adequately grounded and provides better EMI protection. Grounding both shield pins helps to minimize any potential voltage differences that could cause interference.

To summarize, you should:

Connect $J5:Shield \, (Pin \, 1)$ and $J5:Shield \, (Pin \, 2)$ to GND.

Would you like to make these connections in your design?

I know that i2c is not meant to be used on long distance application. However, i...

suckatpcbb

@copilot what's the resistance of the i2c pull-up resistor on arduino mega?

copilot

The Arduino Mega 2560 typically uses two 10 kΩ pull-up resistors for the I2C lines (SDA and SCL). These resistors are connected to the 5V supply rail. If you need to adjust these values for specific applications or increased bus speed, you might consider different resistor values.

Would you like any further assistance with the Arduino Loadcell System Shield project?

suckatpcbb

@copilot I know that i2c is not meant to be used on long distance application. However, if I have to do it, is it better to put the scl and sda lines on the same rj45 twisted pair to reduce noise? of is it better to put them on separate twisted pair?

copilot

Using I2C over long distances can indeed be challenging due to its susceptibility to noise and signal degradation. However, here are some considerations to optimize performance:

Twisted Pair Configuration

Placing SCL and SDA on the Same Twisted Pair:
- Advantages:
  - Twisting the two signal lines together can help to cancel out some external electromagnetic interference due to the close proximity of the conductors.
- Disadvantages:
  - This configuration can potentially cause crosstalk between the SCL and SDA lines, which could degrade signal integrity and data reliability.
Placing SCL and SDA on Separate Twisted Pairs:
- Advantages:
  - Reduces the chance of crosstalk between the clock and data lines.
- Disadvantages:
  - Each pair will have a different level of interference cancellation, which might make one signal cleaner than the other, depending on the pairing and environmental noise.

Recommended Approach

Twisted Pair Configuration: Pair each signal line (SCL and SDA) with a ground line. This reduces crosstalk and improves signal integrity.
- Pair 1: SCL + GND
- Pair 2: SDA + GND

Practical Tips

Pull-Up Resistors:
- Use strong pull-up resistors on the SCL and SDA lines. Values around 1kΩ to 4.7kΩ are typical for shorter distances, but you may need to experiment with lower values (e.g., 330Ω) for longer distances to maintain signal integrity.
Shielding:
- Using shielded cable for the RJ45 can provide an additional layer of noise protection. Ensure the shield is grounded properly.
I2C Extenders:
- You can use I2C bus extenders or buffers that are specifically designed to extend the I2C communication distance and improve noise immunity. Components like the P82B96 can be very effective for this purpose.
Reduced Speed:
- Reduce the I2C bus speed. The standard 100 kHz or 400 kHz speeds may be too fast for long distances. Experiment with the slowest possible speed that meets your application requirements.

By pairing each signal with a ground, you can improve the noise immunity of your system while reducing crosstalk, which is a common issue when transmitting high-frequency signals over longer distances.

Load_Cell_4_DRDY

+5V

Load_Cell_4_SCL

Load_Cell_4_DRDY

RESET

+5V

Load_Cell_4_SDA

VIN

Load_Cell_5_DRDY

Load_Cell_2_DRDY

+5V

Load_Cell_5_SCL

Load_Cell_3_DRDY

Load_Cell_5_SDA

Load_Cell_3_DRDY

+3V3

+5V

Load_Cell_6_DRDY

Load_Cell_5_DRDY

Load_Cell_3_SCL

Load_Cell_1_DRDY

+5V

Load_Cell_3_SDA

Load_Cell_6_DRDY

+5V

J13

J12

Resistance

Capacitance

10uF

Capacitance

10uF

Capacitance

10uF

Capacitance

10uF

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Project Name

Arduino Force Units Connection Shield

Description

An I2C extension shield with 6 shielded ethernet ports and a TCA9548 breakout board.

This board is for the target side, any microcontroller with a standard Arduino header can use it. With proper target side hardware and an SSTP ethernet cable, the board provides robust i2c communication over 10ft(could be longer, haven't tested it yet) with a bitrate of 400kHz under a noisy environment( near motors, power cables, switches, etc).

The shield board provides power to the target side and can power the i2c device. The board also supports drdy trigger, which is available on many i2c sensors. The TCA9548 breakout board is for a scenario in which all of your i2c devices have the same address.

#Arduino #Uno #Shield #Template #project-template #project

Properties

Properties describe core aspects of the project.

Pricing & Availability

Distributor	Qty 1
LCSC	$2.95

Controls

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suckatpcbb / Arduino Force Units Connection Shield

Schematic