Saturday, 17 December 2016

DIY 50mil (1.27mm) to 100mil (2.54mm) adapter for atatmel ice

I've been meaning to try the new cortex m0 chips by atmel but was put off by the high programmer price, fortunately they now sell a bare version known as atatmel-ice-pcba with no case or cables. So after the initial shock of how small the cortex debug connector is I set off to find a cheap way to break this out to 0.1" headers. Fortunately a soic chip has the same footprint as the SMD variant of the mating connector. Flicking through the CPC site to find anything 1.27mm (50mil) I found some soic to dip adapters, after checking the data sheets to confirm it would work I made the order.

Description CPC code Manufacturer code
AMPHENOL FCI Minitek127 10way SMT RECEPTACLE CN18263 20021321-00010C4LF
PROTO ADVANTAGE SOIC-14 to DIP-14 Adapter PC01795 PA0003

Thursday, 1 December 2016

Using the TPLink TL-POE10R PoE Splitter with a Cisco Inline power switch WS-C3550-24PWR-SMI

As part of my Raspberry Pi Zero CCTV project, I've opted to use PoE to get data and power outside to the cameras.

After another hasty ebay spree I ended up with a Cisco WS-C3550-24PWR-SMI 24 port "PoE" switch.  Little did I know Cisco had their own version of PoE before the 802.3af standard arrived called Inline power.

After doing my usual and researching what I've bought after purchasing (and not before) and realizing it wasn't compatible :(  I initially I thought to just return it but after pricing up real PoE or passive PoE compared to what I payed for this switch (£25) it seemed daft to not give it a go.

I took the switch apart and googled some of the part numbers that looked like they may control the Inline power circuit  and I couldn't find any datasheets to see if there was any way to "hot wire" or reverse engineer the circuit.

Anyway after hours of searching Cisco inline power and seeing if anyone else had the pleasure, all I could find were people trying to use inline power phones with 802.3af switches.

At this point the only information I had was that a "PD" echos a low frequency signal back to the switch via a low pass filter which then tells it to enable the power output.

So now the plan is to measure this low frequency signal with my scope and try and reproduce this filter with my own circuit.

By this point I figured a Cisco Inline power phone is going to be the cheapest method of seeing this signal being used and what components are used in the phone.

Back to eBay to acquire a cheap Cisco phone, so £8 lighter and a few days later a CP-7912G-A arrived. Connected it up to the switch and its powered up OK so good news!

Get the screw driver out and take the phone apart and everything is very compact and there isn't the magical silkscreen with labels to the filter PCB that I was hoping for to copy however I did spot some relays which help explain some of the Cisco trouble shooting guides.

TL:DR using some relays to bridge the tx and rx pins on the "normally closed" pins so that it go open circuit when powered is enough to enable the power output and it works no problem with a TL-POE10R