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Project OhmLeds2
Designing successor of Ohmleds
Status Initializing
Contact cmpxchg
Last Update 2020-06-06

Problem description

There is word that ohmleds https://tkkrlab.nl/wiki/OHM_LEDS might not work with all modern switches, due to lack of supporting 10 mbps mode in their PHY of switch fabric. On the other hand, there is demand for new features, like Power-over-ethernet, and a more compact, but still weather-proof design. The OhmLeds design used a microchip ethernet controller with a built-in UDP stack, and SPI link to another microcontroller doing the ArtNet protocol implementation and driving the Leds. A laptop powersupply delivers the power from 230 V. The whole is mounted in a short PVC tube, which is would around with a RGB LedStrip. The whole is mounted using tie-raps to a datenklo. The artnet protocol is used to drive and indicate the status of the datenklo.

Exploring solution space

The SPI link between the microcontroller and ethernet controller is unique for the OhmLight setup. Almost all other microcontrollers use a parallel interface to an ethernet PHY, https://en.wikipedia.org/wiki/Media-independent_interface The idea is to use a microcontroller with such interface.

Ethernet interfacing

On the PHY side, there is the need for power-over-ethernet. This involves three main components, an ethernet transformer that can take off the DC power (20 watts or more), a controller for such power-takeoff (ST has a few options), and a PHY that does the actual ethernet analog signal conversion, clock recovery, and interfacing to the clock domain of the MII interface of the microcontroller. 10 megabit ethernet is very simple encoding, but for 100 megabit ethernet, escape sequences are already defined to define framing, and bandwidth limitations due to that frameing. Idea is to explore the usage of an FPGA to build the digital part of the ethernet PHY.

Mains power

Next to power-over-ethernet, mains power might be needed in PoE is not sufficient or just not working due to vendor-specific implementation details. For this, a discrete 230V to 5V, 40 watt powersupply can be designed on the same, 4-layer board.

LED interface

5 volts, ground, and data/clock soldering pads.