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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 or 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 wound around with a RGB LedStrip. The whole is mounted using tie-raps to a datenklo. The artnet protocol https://artisticlicence.com/WebSiteMaster/User%20Guides/art-net.pdf 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 OhmLed 2013 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.

I would like to explore the space of such solution, since this also allows for PoE (power over ethernet)

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
  • an ethernet PHY that does the actual ethernet analog signal conversion

PoE Ethernet transformer and circuitry

The STEVAL-POE002V1 SCHEMATIC is available https://www.st.com/content/st_com/en/products/evaluation-tools/solution-evaluation-tools/psu-and-converter-solution-eval-boards/steval-poe002v1.html#resource

It lists many of the electromagnetic components, that are critical in the power-conversion process, and have a lot of parameters that need to be designed in. Thus understanding these choices and optimizing them for our application is critical.

Designator Comment Manufacturer/partno datasheet
T1 main PoE power-takeof transformer CoilCraft eth1-460 https://www.coilcraft.com/eth1-460.cfm
T1 alt Wurth TBD TBD
T5, T6 SMT power filtering transformers Wurth 744272102 https://www.we-online.com/catalog/datasheet/744272102.pdf
T7, T8 alt for T5,T6, not mounted
Figure 3 T2 DC common mode filter, not mounted
T2 Power Inductor (SMD), 5.6 µH, 7.2 A, Shielded, 6.3 A Coilcraft XAL5050-562 5.48mm x 5.28mm x 5.1mm https://www.coilcraft.com/pdfs/xal50xx.pdf
T3 High Power PoE/flyback Transformer CoilCraft NA6083-BL https://www.coilcraft.com/pdfs/ra7129.pdf
T4 gate driver transformer 1:1 COILCRAFT DA2319-AL https://www.coilcraft.com/pdfs/da23xx_gate.pdf
L4 120nH power inductor 20% DCR=0.0015 28A/17A COILCRAFT DO3316H series https://www.coilcraft.com/pdfs/do3316h.pdf
U3 optocoupler OnSemi FOD817AS https://www.onsemi.com/pub/Collateral/FOD814-D.PDF
U4 Low voltage adjustable shunt reference ST TS432 AILT SOT23-5 https://www.st.com/content/st_com/en/products/power-management/voltage-references/ts431.html
Q1 power MOSFET N ch 60 V 10 milli max Qt <30nc ST TBD check spec STL110NS3LLH7 (??) https://www.st.com/en/power-transistors/stripfet-f7-series.html
Q1 alt TBD: check spec power MOSFET N ch 60 V 10 milli max Qt <30nc Infineon BSC039N06NS https://www.infineon.com/cms/en/product/power/mosfet/12v-300v-n-channel-power-mosfet/bsc039n06ns/
Q4 power MOSFET N ch 150-200V 50 milli max Qt <30nc OnSemi/Fairchild FDMS86252 woerflat 5x6 https://www.onsemi.com/pub/Collateral/FDMS86252-D.pdf
Q4 alternative TBD: check specs MOSFET N ch 150-200V 50 milli max Qt <30nc Infineon BSC500N20NS3G https://www.infineon.com/cms/en/product/power/mosfet/12v-300v-n-channel-power-mosfet/bsc500n20ns3-g/

PoE controller/circuitry

This is a combination of many cheap passives, and a PoE controller. ST has a few options https://www.st.com/content/st_com/en/campaigns/PoE_supply_reference_designs.html

One 8A, 5V solution might be great for driving many Leds, since their forward voltage is typically around 3 volt and are controlled using PWM.


  • PM8805 4-pair IEEE 802.3bt compliant PD interface (ca EUR 5.00 / 100 pcs)
  • Output stage managed by configurable PM8804 controller (ca EUR 1.05 / 100 pcs)
  • Output voltage: 5 VDC ±2.5%
  • Output current: 8 A
  • Works with power supplied from Ethernet LAN cables or local auxiliary sources
  • Line input voltage range: 40 to 60 VDC
  • Peak-to-peak output ripple: <50 mV
  • DC-DC full load efficiency: >91%
  • Overall full load efficiency: >90%
  • Transient response ΔV pk-pk 100% to 50% load step ≈ 700 mV
  • Switching frequency ≈ 280 KHz

Ethernet PHY

There are many solutions, but no offerings from NXP or ST. RealTek, Texas Instruments, Analog Devices, Intel.

This part does the clock recovery, converting via a small (!) fifo to the clock domain and parallel interface of the MII interface of the microcontroller. This part should be reliable, no 'packets of death' should bring this link down, for example, as reported already in februari 2013 in this article, bringing the link down after triggering on seemingly arbitrary bytes at a specific offset in the ethernet frame: https://www.theregister.com/2013/02/06/packet_of_death_intel_ethernet/

Realtek RTL8201F 10/100Mbps Ethernet PHY MII/RMII interface https://datasheet.lcsc.com/szlcsc/Realtek-Semicon-RTL8201F-VB-CG_C45044.pdf
Analog Devices ADIN 1200 10/100 PHY 10BASE-Te/100BASE-TX IEEE® 802.3™ compliant

MII, RMII and RGMII MAC interfaces 100BASE-TX RGMII latency transmit: <124 ns, receive <250 ns 100BASE-TX MII latency transmit: <52 ns, receive <248 ns


Discrete Ethernet PHY

Building a PHY from discrete logic/small FPGA might be explored too. Idea is to explore the usage of an FPGA to build the digital part of the ethernet PHY. 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.


This is the application-specific part, it depends on PHY interface. It needs software to control the ethernet PHY, configure the PHY It needs a small network stack implementing DHCP and UDP It needs an application implementing ArtNet protocol (minor part) It needs a peripheral to control the leds via SPI, serial, a parallel fifo ST has MII/RMII interface microcontrollers:

hi-end: STM32F469BIT6 2 MByte flash and 384 kb SRAM should be enough for an embedded networking stack https://www.st.com/resource/en/datasheet/stm32f469bi.pdf

low-end STM32F107RB 64 kbyte flash, 64 kbyte SRAM - not a lot for a network stack! https://www.st.com/content/st_com/en/products/microcontrollers-microprocessors/stm32-32-bit-arm-cortex-mcus/stm32-mainstream-mcus/stm32f1-series/stm32f105-107/stm32f107rb.html

Newer L4 and L5 series does not seem to have ethernet peripheral variants

LED interface

5 volts, ground, and data/clock soldering pads. How simple could it be ?

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.