PoE Pi : Powering a Raspberry Pi with Power over Ethernet

Power over Ethernet (PoE) is a standard for powering devices over an ethernet cable. Aside from the IEEE 802.3af standard (description) there are other ways of powering devices over ethernet cables.

Shopping on internet shows two different PoE solutions, the cheap (and slightly sloppy and maybe dangerous) way is to use unused pairs in the Cat 5 cable and use a passive injector and splitter. The problem with that solution is the dissipation and loss in the network cable at higher powers. The nicer and safer solution is the official IEEE 802.3af solution that I wanted, and I wanted this to work with thin 2-pair Cat 5 cable. Regular Cat5 cable has 4 pairs. I’ll only be using the IEEE 802.3af standard here.

I bought a (second hand and very loud) Cisco Home Office PoE switch to try this all out.

2 Pair Cat-5

I bought a PoE splitter from Aliexpress

The PoE splitter was fairly cheap (about 7 euro) and there were some doubts if this was actually an active splitter. The sticker on the back states IEEE802.3af compatibility.

The insides seems legit,an actual PoE controller chip, isolating transformer and Ethernet transformer. The parts used look like the application note with one difference : the application note describes a 10/100/100 MB/s solution with 4 wire pairs, this splitter only supports 2 pairs.

IMG_20160528_213953

The track clearance is not great though. And there is something going on with the connections between two cable pairs but this configuration seems to be used in other setups as well ( figure 4, figure 1.1 ).

IMG_20160528_213922

These PoE splitters deliver 12 V. The raspberry Pi needs 5 V on the micro USB port. I’ll need to convert it to 5 V.

Aliexpress and other sites sell step down converters. I bought these, trimmed it to 5 V. and fixated the pot with nail polish.

I sacrificed a USB cable, added a barrel jack and hotsnotted it al in place.

IMG_20160325_224105

IMG_20160325_224116

Success ! The setup works with RTL-SDR on a Raspberry Pi.

Someone built a Modular Analog Synth

As seen on the stand of the dutch electronics forum Circuitsonline at the VERON Fleamarket : a home built modular synthesizer.

It’s hard to find more information, all i have found is the forum post (in dutch : translation here).

The setup is similar to the Elektor Formant and Compact and the modules from Doepfer. Of course those are all inspired by the Modular Moogs.

The use of PCB as frontpanel is innovative. It’s a clever solution: PCB can be made cheaply and easily, in all sorts of colors and with text. Mikes electric stuff explains how and why.

I hope to find more information about this machine, a kit like this needs to be heard as much as seen.

Alpha Clock Five

In return for helping out at Makerfaire Eindhoven, Pieter from Floris.cc gave me a Alpha Clock Five kit from Evil Mad Scientist.

The kit is very well documented (schematic and sourcecode), uses only though hole components and is easy to assemble.

Aside from the Atmel and Chronodot stuff it uses two interesting IC’s : Macroblock MBI5027 and Macroblock MBI5168

Another nice thing about the Alpha Clock Five is the Serial protocol that allow you to control all aspects of the clock.

The software is really polished, no flickering display, nice gradient while dimming, user definable characters. The only thing missing you could possibly want is different intensities per segment.

Baking Impees

A jig to keep the boards and stencil in place

The large blobs make it hard to find the right place for the components

Having cheap PCB’s made

The PCB’s for the kits and projects on this blog are made by cheap manufacturers. These manufacturers don’t especially cater to hobbyists but would like to have filler orders to keep production running when there are no large orders available. The PCB manufacturers sell this production time cheaply, the downside for the customer is the long or uncertain delivery time.

When shopping for PCBs you can sometimes tweak two parameters : the delivery time and the number of boards. A longer delivery time will lower the cost, a larger number of boards will raise the total cost but in general lower the cost per board, sometimes by a lot.

The manufacturers will typically want you to deliver gerber files. Making and checking gerbers is a blogpost by itself, the BatchPCB FAQ has an entry about them and Sparkfun has a tutorial. Before I have PCB’s made I check them at circuitpeople.com and if the board is really new I usually render it with Eagle3D.

Here is a list of PCB manufacturers I have used and some that I have not yet used but offer interesting services.

MakePCB

MakePCB is by far the cheapest PCB manufacturer I have found. The site is not as detailed as the competitors site and the communication is not very helpful at all. The price is unbeatable. I have used their service in the past expect to use them in the future.

Price : http://www.makepcb.com/
Specs : – here –

BatchPCB

BatchPCB is Sparkfun’s PCB Pooling service. The designs are panelised by BatchPCB and the panels are made and cut by by Gold Phoenix and sent to the US in bulk. BatchPCB then sends out the PCB’s to the end customers. Specs and tolerances can be found here, prices are here. BatchPCB is a great service and offers other services like selling your boards to other users. I have stopped using BatchPCB because BatchPCB is expensive and located in the US. Sending boards from China to the US and sending them from the US to Europe adds to the cost and delivery times.

Eurocircuits

Eurocircuits have their own manufacturing and pooling service. The quality of the boards is high and the price is too. Where MakePCB keeps communication to just below the bare minimum, Eurocircuits has a hand-full of sites in different languages, and a coice of 4 or 5 different PCB services. The result is pretty confusing. The price calculator is shared between all sites but needs magic parameters in the URL to determine the price. I suspect they have different prices for different kinds of customers. Eurocircuits have been partnering with Elektor and offer Elektor PCB’s no longer offered by Elektor themselves.

Price : – here –
Specs : – here – (in a PDF)

Board and price examples

Say we’d like to have 25 Arduino shields made. The shields are double sided, with double sided solder mask and a single silkscreen. The PCB’s are not rectangular but have the traditional Arduino Shield bump and holes. The board is 69 x 53 mm. Shipping is to the Netherlands.

Manufacturer	clearance	trace	via	Price 1	Price 25	S&H 1	S&H 25	Total 1	Total 25	Lead time
MakePCB	0.2 mm (8 mil)	0.2 mm (8 mil)	0.3 mm (12 mil)	26.72 €	56.76 €	6.21 €	14.73 €	32.48 €	71.49 €	about 4 weeks
BatchPCB	8 mil (0.2 mm)	8 mil (0.2 mm)	20 mil (0.5 mm)	15 USD	375 USD	about 18 USD	about 18 USD	33 USD	393 USD	about 20 days
Eurocircuits	8 mil	8 mil	0.35 mm	53.81 €	121.13 €	10.01 €	10.16 €	63.81 €	131.29 €	about 30 days

Other PCB services

There are a couple PCB services that I have not used yet but that seem to offer interesting services.

Gold Phoenix PCB

Gold Phoenix PCB is the manufacturer that supplies the PCB to BatchPCB. BatchPCB collects orders to fill up panels. Once a panel is full, BatchPCB has the panel made, cut up to the individual boards and sent to BatchPCB. This “buy a panel” service is also available to end users. The panel sizes for 2 layers are 1000 cm² or 650 cm². The shield in this example has an area of about 37 cm². One panel would yield 27 Arduino shields. Gold Phoenix is a bit more expensive than the cheapest option I have used but is interesting because they support tighter tolerances and, for a fee, inner cuts, different color soldermasks and different color silkscreens. You could do stuff like white PCB’s with black lettering.

PCB-Pool

PCB-Pool is one of the older PCB manufacturers that offer their services online. PCB-Pool is interesting because the offer solder paste stencils, sometimes for free. They also have a Front panel service.

Price : – here –
Specs : – here –

More price examples

Two notes about the prices here :

In this example PCB-Pool will make 30 PCB’s for the same total price as 25. Apparently they are filling panels.
In this example GoldPhoenix will make 27 PCB’s.

Manufacturer	clearance	trace	via	Price 1	Price 25	S&H 1	S&H 25	Total 1	Total 25	Lead time
GoldPhoenixPCB	7 mil	7 mil	15 mil	99 USD	99 USD	10 USD	10 USD	109 USD	109 USD	8 working days
PCB-Pool	0.15 mm (6 mil)	0.15 mm (6 mil)	0.3 mm (12 mil)	43.73	198.30 Euro	?	?	?	?	?

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