Cisco – Experimental Engineering

Posted on October 22, 2015 by The Engineer — Leave a comment

Netgear GS308 Gigabit Switch

Here’s a new addition to the network, mainly to replace the ancient Cisco Catalyst 3500 XL 100MB switch I’ve been using for many years, until I can find a decently priced second hand commercial gigabit switch.

Here’s the switch with some network connections on test. So far it’s very stable & draws minimum power. I’ve not yet attempted to run my core links (NAS) through yet, as I’ve not yet seen a consumer grade switch that can stand up to constant full load without crashing.

Here’s the switch with it’s lid popped. The magnetics can be seen at the back, next to the RJ-45 ports, the large IC in the centre is the main switching IC, with a heatsink bonded to the top. Very minimal design, with only a couple of switching regulators for power supply & not much else.

Here’s a closeup of some of the support components. There’s a 25MHz crystal providing a clock signal for the switch IC, just to the right of that is an EEPROM. I imagine this is storing the switch configuration & MAC address. Further right is one of the switching DC-DC converter ICs for power.

As a quick test, here’s 500GB of data being shifted through the switch, at quite an impressive rate. I’m clearly maxing out the bandwidth of the link here. Soon I will upgrade to a 10G Ethernet link between the NAS & main PC to get some more performance.

Posted on September 27, 2015 by The Engineer — Leave a comment

DIY SMPS Cooling

The power supplies I have recently built from surplus Cisco switch boards have started displaying a rather irritating problem – continual load of over 9A causes the supplies to shut down on overheat.

This was partially expected, as the original switches that these supplies came from are cooled by a monster of a centrifugal blower that could give a Dyson a run for it’s money. The problem with these fans is that they’re very loud, draw a lot of power (3-4A) and aren’t small enough to fit into the case I’ve used for the project.

The solution of course, is a bigger fan – I’ve got some Delta AFB0612EHE server fans, these are very powerful axial units, shifting 60CFM at 11,000RPM, with a power draw of 1.12A.
They’re 60mm diameter, so only just fit into the back of the case – although they stick out of the back by 40mm.

Here’s the fan, not the beefiest I have, but the beefiest that will fit into the available space.
These will easily take fingers off if they get too close at full speed, so guards will definitely be required.

To reduce the noise (they sound like jet engines at full pelt), I have ordered some PWM controllers that have a temperature sensor onboard, so I can have the fan run at a speed proportional to the PSU temperature. I will probably attach the sensor to the output rectifier heatsink, since that’s got the highest thermal load for it’s size.

More to come when parts arrive!

73s for now 🙂

Posted on July 25, 2015July 29, 2015 by The Engineer — Leave a comment

13.8v SMPS PSU Build

A while ago I blogged about modifying the output voltage of some surplus Cisco switch power supplies to operate at 13.8v.

Since I was able to score a nice Hammond 1598DSGYPBK ABS project box on eBay, I’ve built one of the supplies into a nice bench unit.

Above is the supply mounted into the box, I had to slightly trim one edge of the PCB to make everything fit, as it was just a couple of mm too wide. Luckily on the mains side of the board is some space without any copper tracks.

These supplies are very high quality & very efficient, however they came from equipment that was force-air cooled. Running the PSU in this box with no cooling resulted in overheating. Because of this I have added a small 12v fan to move some air through the case. The unit runs much cooler now. To allow the air to flow straight through the case, I drilled a row of holes under the front edge as vents.

Here is the output side of the supply, it uses standard banana jacks for the terminals. I have used crimp terminals here, but they are soldered on instead of crimped to allow for higher current draw. The negative return side of the output is mains earth referenced.

I have tried to measure output ripple on this supply, but with my 10X scope probe, and the scope set to 5mV/Div, the trace barely moves. The output is a very nice & stable DC.

This supply is now running my main radio in the shack, and is small enough to be easily portable when I move my station.

Posted on July 8, 2012 by The Engineer — Leave a comment

Cisco 2G Fibre Channel SFP Module

2G Fibre Tranciever — 2G Fibre Transceiver

Here is a 2Gbit Fibre Channel transceiver from Cisco Systems in SFP module format.

Here the shield has been removed from the bottom of the module (it just clips off). The bottom of the PCB can be seen, with the copper interface on the left & the rubber boots over the photodiode & 850 nm laser on the right.

Here the PCB has been completely removed from the frame, the fibre ends slide into the rubber tubes on the right.

Top of the PCB, showing the chipset. There are a pair of adjustment pots under some glue, next to the chipset, presumably for adjusting laser power & receive sensitivity. The laser diode & photodiode are inside the soldered cans on the right hand side of the board, with the optics required to couple the 850nm near-IR light into the fibre.