I received noticed from UPS that there is a package on route to me. I will assume it is the equipment for this RoadTest. I have no other items I am waiting to receive. I didn't click the link to confirm. I'm hoping it not just a UPS related phishing attempt. Oh well, let's post some theory for this RoadTest in the mean time.
What is Power over Ethernet (PoE) as it relates to this device. With the Microchip PoE, a USB-C powered device can get power over the same cable that carries network data. In Scenario A drawing, the Network switch is designed to provide power and data over the network cable. In the top drawing, the Microchip PoE device is interfacing the power and data to the Pi Zero. In the lower pictorial from Scenario A, you have a Pi with a PoE HAT that interfaces power and data to the Pi4B+.
Some additional details in the scenario. The devices are attached back to the Network Switch on 100 meters of CAT 6. The Network Switch is connected to a device that provides Internet access. In this case a Internet Gateway. The Pi Zero or Pi4B+ can gain access the Internet over the cable and be powered from that same cable.
In Scenario B, the PoE support network switch is replaced with a regular switch. A regular switch doesn't supply PoE power on it outputs. To support this design a PoE injector or PoE power supply is added to the circuit. The injector provides the power out to the end devices. The PoE injector takes data connection on one side and feeds power and data out the other connection. The PoE injector is plugged into a wall outlet to get it power.
To complete this RoadTest Scenario B will be used with a TP-Link Gigabit PoE injector TL-POE150S deployed. Not all PoE power providing devices are the same. I have another PoE power supply that I have used in the past The Road to Raspberry Pi4B/ PoE Hat RoadTest Review (power supply) . I discovered the device limits the data throughput on the network to 100Mb's, down from 1G. Since this RoadTest includes a data components, The TP-Link injector is the being used to ensure the highest data throughput.
Hey wait a minute, a Pi Zero doesn't have an Ethernet connection! Besides it's power is via a USB mini and not USB-C connector. The different power connectors can easily be accommodated with adapators. The data requires something more. That is where On-The-Go (OTG) technology comes into play.
The PiZero power connector supports a data output. The same can be said for the Pi4B+. The power connector (USB mini for PiZero and USB-C for the Pi4B+) has data capabilitie using OTG. The initial blog post for this RoadTest Microchip PoE to USB-C
Power and Data Adapter RoadTest Review Introduction provides some insight.
I am hoping (again not sure), the Pi OTG will provide a network data connection. That would enable a wired network to a PiZero. It also would provide a wired network connection to the Pi4B+ without using the Ethernet adaptor.
In addition to achieving data connection, the end device needs to be loaded down so it draws maximum power from it's supply. The network cable has considerable length, this provides resistance that can impact power. Creating a heavy load on the end device ensures all the components in the chain work effectively if the end device is to function correctly. The TP-Link injector has been used in the past as a power source with good success. Will the Mircochip PoE supply added to the chain, can it supply the needed power?
