I bought a generic branded IP Camera from eBay.
It featured POE support, but unfortunately things don’t always go to plan…
POE - Passive and Active
POE stands for Power Over Ethernet; and is a way of supplying power over an Ethernet cable. This makes connecting remote devices a breeze - as you no longer need to think about how to get both data and power to the device.
There are two main types of POE connections - Passive POE and Active POE.
There are also different “POE Modes” - but here I will only cover the main one, Mode B / Midspan.
Passive POE
In an Ethernet cable, for 100 Mbit operation, only pins/wires 1, 2, 3 and 6 are used (For Mode B).
Passive POE functions by injecting electricity into the unused pins 4-5, and 7-8.
The device on the other side can then have those powered pins, wired as their voltage source.
With Gigabit / 1000 Mbit Ethernet, all pairs of the wire are used.
Passive Gigabit POE still injects power into these wire pairs, but a “center-tapped transformer” is used to extract the power. It reminds me of Phantom Voltage / +48V when it comes to XLR cables for audio
There exists Passive POE injectors to inject power into the Ethernet cable; and Passive POE splitters to extract the power from the Ethernet cable.
Passive POE is considered ‘dumb’ - as their is no smart / regulating technology as you will see in Active POE.
This creates a tradeoff - Cheapness of Passive POE, versus the danger of accidentally connecting a device that does not support Passive POE, and damaging the device.
Active POE
Active POE performs a negotiation with the end device, to confirm if the device requires POE; and if so, what voltage is needed. They use the 802.3af, 802.3at and 802.3bt protocols.
The cost of Active POE devices is quite high - especially for the POE switches.
They are much safer than Passive POE devices, as nothing will go bad if you connect an Active POE injector / switch / source to a device that does not require POE.
A helpful article by Ubiquiti: Intro to Networking - Power Over Ethernet (PoE)
The Camera
Upon receiving the camera, I tried to connect it to the 12V 1A POE Injector, however to no avail. Powering the camera through the DC barrel jack works, so I had a suspicion that either my POE Injector was faulty, or there was something wrong with the camera.
I got my multimeter out, and tested the POE injector… I was definitely getting 12 volts of potential from the 4-5 and 7-8 pairs - So it must be the camera.
The Breakdown
You can open the camera by twisting the base plate off, and popping the camera through the mounting shell.
Then you can twist the camera as well to open it up.
Inside reveals the circuitry.
The thing that first stood out to me was the microchip with the print Smart POE HN1602CG.
After some Google-ing, I found a datasheet for the chip.
It’s described as a “10 / 100 Base-T Single Port Transformer” that is “IEEE 802.3 Ethernet Compatible, 10 / 100 Base-TX”
“802.3” - Yep it’s an Active POE device - meaning that my Passive POE Injector was unusable, without buying a Passive POE splitter.
But, hey… I’m an Electrical Engineering student… My degree is somewhat useful right???
Surely I can find a way to get it working!!!! (Right?????????)
The Modification
The camera requires a 12VDC power supply into the DC barrel jack of the camera, or an 802.3 POE supply into the Ethernet. I had a 12V Passive POE injector that supplied power into pins 4-5 and 7-8 of the Ethernet cable.
I could rewire the pins, and route the Passive POE into where the 12V barrel jack goes!
Firstly, I needed to get a pin-out of the circuit board.
There were 11 wires coming out of the camera’s external cable.
| Ethernet T-568B Colour | Wire Colour | Circuit Port | Purpose |
|---|---|---|---|
| Orange White | Blue White | R1 | Data |
| Orange | Blue | R2 | Data |
| Green White | Green White | R3 | Data |
| Blue & Blue White (Bridged) | White | 4 / 5 | + POE |
| Green | Green | R6 | Data |
| Brown & Brown White (Bridged) | Yellow | 7 / 8 | - POE |
| - | Red 1 (Bridged) | +12V | Power |
| - | Red 2 (Bridged) | +12V | Power |
| - | Black 1 (Bridged) | GND | Power |
| - | Black 2 (Bridged) | GND | Power |
| - | Purple | L+ | LED |
There were three circuit boards in the camera.
- POE board - Extract 802.3 POE, and to pass cables to the other boards
- Control board
- Camera board
There were two sets of black and red power wires, one set which went to the POE board (which connects to the control board), and the other set to the camera board.
The power wires seem to be bridged from the external cable; meaning that if I were to splice the Passive POE wires - it would have to be either from the external cable, or I’d have to tap the power wires.
Luckily, I had these scotch locks (2-wire type, but they will do the job still).
I disconnected the yellow and white wires, and spliced a set of black and red wires.
I then put both cut ends of the black wire into one port of the scotch lock, and the yellow wire into the other.
Press on the lock, and crimp it with a plier - done!
After doing the same thing with the red and yellow wires we’ve got something that looks like this.
Connecting the power… everything works! Hooray!
The Installation
The first thing was to run an Ethernet (CAT5E) cable from underneath the house to the roof.
Up we go!
After that, on the other side of the roof - pull the cable and install the camera.
Clean up the cables, and… voila!
Lastly, I just had to cut some wires to connect the injector to.
Plug it in, and we’re done!
Conclusion
I’m pretty happy that everything worked out at the end.
Yes, I could have just bought a $3 Passive POE splitter, or just fork up some cash for a 802.3 switch or injector, but this was way more fun!
Also, rtsp://[IP ADDRESS]:554/stream0
