Hardware Assembly; Ethernet Cables - sparkfun QwiicBus COM-18000 Hook-Up Manual

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The QwiicBus EndPoint PCB measures identically to the Differential I C Breakout at 1.75in x 1.00in (44.45mm x
25.40mm). The MidPoint measures 1.80in x 1in (45.72mm x 25.40mm) and is flared to 1.10in (27.94mm) wide at
the RJ-45 end. The RJ-45 connectors extend roughly 0.30in (7.62mm)from the edge of the PCB on both boards.

Hardware Assembly

In this section we'll go over configuring your QwiicBus EndPoint and MidPoint as how to assemble the QwiicBus
circuit. Before we start connecting anything there are a couple of things to take note of.

Ethernet Cables

Make sure your Ethernet cables are straight-through (i.e. Pin 1 on one end of the cable is connected to Pin 1 on
the other end) and not crossover. Most Ethernet cables sold are straight-through so you probably have nothing to
worry about here. If you're not sure what type of Ethernet cable you have, you can test for pin continuity with a
digital multimeter.
Also take the voltage drop over the Ethernet cables into account. For longer chains or for circuits with many
devices on multiple MidPoints, consider using one of the alternate power configurations so the voltage drop is
negligible. The formula below can help you calculate the voltage drop at different lengths of CAT-6/Ethernet cable
and whether or not you will need to consider one of the alternate power options:
In this formula, I is the current through the object in Amperes and R is the resistance of the wires in Ohms. Most
CAT-6/Ethernet cable will have 24AWG internal wires and depending on the quality of the cable will be either
copper or aluminum. Refer to a table like this one from PowerStream to determine the resistance in Ω/1000ft or
Ω/km to help calculate the approximate voltage drop.
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I C Pull-Up Resistors
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Take time to note which devices you will have connected to your EndPoint and MidPoint's I C bus side have their
pull-up resistors enabled and what voltage they are tied to. Almost all Qwiic products have pull-up resistors
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enabled by default that pull the SDA/SCL lines connected directly to the I C bus to 3.3V.