1
\$\begingroup\$

I'm trying to make the OpenMV Cam M7 PoE enabled. See the link below for the camera:

https://openmv.io/collections/cams/products/openmv-cam-m7

It has USB interface, SPI, UART and CAN buses. My initial thought is to use a PoE splitter and send power through the USB and then convert the ethernet to SPI or UART, but I'm looking for more ideas. The network switch conforms to the IEEE 802.3af standard, and the splitter steps it down to 5V, which the microcontroller board can tolerate.

\$\endgroup\$
1
  • \$\begingroup\$ There are pseudo POE kits available \$\endgroup\$
    – Voltage Spike
    Jun 15, 2017 at 19:32

3 Answers 3

1
\$\begingroup\$

If your device uses only 100base-T ethernet, you can use the cheap and simple PoE protocol used by inexpensive IP cameras. 100base-T uses only two pairs of the 4-pairs in a standard cat-5 cable: orange & green (plus their respective white-stripe conductors). The otherwise-unused blue and brown pairs are used to supply power to the camera. Most IP cameras used 12 Vdc as the PoE source.

This technique was specified in the IEEE 802.3 standard in 2003. It is known as "Alternative B" and places the positive voltage on pins 4&5 (blue pair) and ground on pins 7&8 (brown pair).

You can purchase inexpensive adapters or simply roll your own.

\$\endgroup\$
0
\$\begingroup\$

I haven't tried it myself yet, but one of these should do the trick: http://skpang.co.uk/catalog/enc28j60-ethernet-module-with-spi-bus-poe-circuitry-33v-p-313.html . However it would require you to power the OpenMV from 3.3V. Looking through the specs, it seems (10 seconds research) to run on 3.3V however needs a 3.6V power supply, probably to overcome the voltage drop. Possibly you could just supply 3.3V to the 3.3V pin and things will work.... Or not...

I'm actually about to buy some to try powering a raspberry pi from it!

\$\endgroup\$
2
  • \$\begingroup\$ Be careful with that product, because it does not step down the 48V from 802.3af switch to the ~3.6V you need for the board. \$\endgroup\$
    – Alex H.
    Jun 19, 2017 at 19:14
  • \$\begingroup\$ You are right! I was fooled by the 3.3V in the name, I guess that the SPI voltage :(. I guess this board is just an SPI ethernet and breakout for the ethernet pins needed to implement one's own (pretty complex) circuitry... Thanks! \$\endgroup\$
    – Claude
    Jun 20, 2017 at 8:26
-1
\$\begingroup\$

Through the use of phantom power—power sent over the same wire pairs used for data, the same pair is used for both power and data, the power and data transmissions don’t interfere with each other because electricity and data function at opposite ends of the frequency spectrum, they can travel over the same cable. Electricity has a low frequency of 60 Hz or less, and data transmissions have frequencies that can range from 10 million to 100 million Hz.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.