Access a Cisco Switch via USB Console

It may be that you want to use a USB cable, or it may be that just like me you forgot your USB to serial adapter, and now your faced with connecting to a Cisco switch with a USB cable rather than the serial cable on OSX.

Well how do we go about this, with Windows we could simply look up the port number in device manager, with OS X they do not use this reference, instead referring to the device as a TTY USB modem.

First we need to look up the device, which is contained with other devices in the folder /dev/, we also want to limit it to devices of the USB type so we are going to limit the command to that. Open terminal and type the following command;

ls -ltr /dev/*usb*

This will list all devices in the /dev/ directory (the devices directory) where it contains the key phrase usb within it, with all information, in a list with the most recently modified device (and therefore most likely the device we are looking for)

Your device will show up as something such as


Now we have the path to the device, we need to open a console using it. In OS X the console utility screen is built in, so lets open it utilising this utility and a baud rate of 9600 which most devices will happily handle. To do this type;

screen /dev/tty.usbmodem.12a1 9600

What this command is stating is open screen on device /dev/tty/usbmodem.12a1 utilising a 9600 baud rate, no settings for stop bits etc are input, you can also utilise other baud rates if needed.

Your terminal will now connect to the console of the Cisco device, this should also however work for any other devices that utilises a USB chipset to communicate via serial emulation.


Creating a USB to DC socket power cable (for an Iridium 9555)


As part of my travel kit I generally take a Satellite phone for emergency communication either out, or more commonly in from work colleagues. With my old one having died, I replaced it with an Iridium Model 9555, and whilst the phone is new, and is a current model it works along the same lines of phones from the early to mid-2000’s. Along the same lines of these phones, the phone uses a wall transformer wired into a standard DC power plug (3mm barrel diameter in this case). This leads to a plethora of adapters to keep the thing charged around the world, and adds to the things that I need to carry with me, and as you may have seen with my other posts I am trying to travel with less, not more.

2015-01-12 - DC Cable - 01 - PhoneThe Phone in Question

2015-01-12 - DC Cable - ChargersStandard Chargers & Adapters for Iridum 9555

Having a look at the chargers in an effort to see if I can eliminate them and use a charger that I already carry to charge the phone. Through looking at the details on the chargers a little measurement and testing of the chargers output 6V DC at 850mA output in a tip positive/barrel negative configuration. I found this rather interesting that it is using 6VDC, as it is very close the the USB voltage of 5V.

USB chargers these days are rather ubiquitous around the place, and with most chargers putting out 5VDC at around 1 amp and going up to 2.1 amps for tablet devices. Given this a USB charger should be able to power and charge the phone, however depending on the tolerances in the chargers output, and the phones required input it may accept a straight input from the USB charger, or it may need to be boosted through a boost converter to achieve this. Either way it means I can do away with all the adapters and simply use the USB chargers I already have to carry.

Looking at the boost converters such as the LM2577 and XL6009 based converters from eBay are capable of this, but first I want to see if I can charge the phone without the converters. Either way I need to make the same cable, with the converter if I need to add it later I can simply cut the cable and insert it in the middle.

Now to start, to complete this project only basic tools are needed; wire strippers, cutting tools, soldering iron (with solder). I used several different cutting tools but you can use whatever you want.

2015-01-12 - DC Cable - 03 - ToolsTools (Soldering Iron, Solder, Wire Strippers, Scissors & Scalple)

I also use a liquid to help the soldering process, this is called Bakers Soldering Fluid, I cannot recommend this stuff highly enough it is simply fantastic, and you do not need much of it, as such a bottle lasts for ages.

2015-01-12 - DC Cable - 04 - BakersBakers Soldering Fluid

As for the parts I used these are shown below, these include; USB Cable with a width of 3.3mm on the cable insulation which is less than the inner diameter of the hole for the DC power plug shroud which is 4mm. It is important to note that the “donor” cable is a USB to Micro cable, as all the full size cables (i.e. not mini or micro connectors on one end) were too wide to go into the plugs shroud. The DC power socket itself has a 3mm barrel on it, beyond that any plug should work. Also two pieces of heatshrink are used, one 4mm and the other 4.5mm. With this you can then create a USB to DC adapter.

2015-01-12 - DC Cable - 05 - PartsUSB Cable, Heat Shrink & DC Power Plug

The first step is to remove the desired head of the USB cable, in my case this is the Micro-USB head

2015-01-12 - DC Cable - 06 - Head RemovalCutting the head off the Cable 2015-01-12 - DC Cable - 07 - Head RemovedCable without Micro-USB Connector

After cutting the connector off the cable, the next thing to do is stripping the out insulation off the cable, thereby exposing the contents inside

2015-01-12 - DC Cable - 08 - Stripping the CableStripping the Cable

This exposes the two types of shielding that protect the inner conductors protecting the lines from EMI that can induce data errors. This shielding causes problems I will go into a below, it is however messy and causes some extra work, it is also not necessary for our purposes.

2015-01-12 - DC Cable - 09 - Cable ShieldingThe shielding on the USB cable

This shielding as per the USB specification is meant to be grounded to the chassis ground, which is no the same as the signal ground that is on the conductor inside the shielding. Whilst this shielding serves no purpose as DC jacks only have the two connections and no shield ground as there is in other connectors. In the creation of the cable can create an issue with causing a grounding loop if it is put directly against the bare metal of the barrel connection to which the inner ground (negative) conductor is to be connected to as these cables are commonly supported by the extension of this barrel connector, as such it needs to be removed as much as possible to do this we first strip it back and expose the insulated inner conductors

2015-01-12 - DC Cable - 10 - Stripped SheildingOuter wire shield pulled back, exposing the inner foil shield (Note how many wires are on the paper under the shield, this can be messy)

2015-01-12 - DC Cable - 11 - Both SheildsBoth Shields pulled back exposing the inner conductors

To make this easier I take the shields and twist them together, much like twisting the bare conductors together before tinning them to make it a cleaner job.

2015-01-12 - DC Cable - 12 - Wrapping SheildsTwisted up foil & wire shielding

Once it is twisted up, cut it off. For this I use some sharp scissors, although this could be achieved with most cutting devices, I like these scissors

2015-01-12 - DC Cable - 13 - Cutting ShieldsRemoving the shielding

Once this is done, I slip the shroud from the DC plug over the cable, and although this could have been done earlier or later in the process I find this is the best time to do it as the mess from the shielding has gone, and the heatshrink has not yet gone on, thereby expanding the cable diameter and making it harder to get the shroud on.

2015-01-12 - DC Cable - 14 - Place ShroudShroud placed on the cable

Sliding the shroud down the cable and out of the way for now I cut heat shrink just big enough to cover the end of the cable and ensure the last of the shielding that is hard to remove will not short against the barrel plug.

2015-01-12 - DC Cable - 15 - Heatshrink SizeCut heat shrink showing the size and the exposed remnants of the shielding

Once the cable is done, thread it over the cable so it covers the remnants of the shielding and shrink it into place

2015-01-12 - DC Cable - 16 - Heatshrink PlacementHeatshrink in place over the cabling protecting the remnants of the shielding

2015-01-12 - DC Cable - 17 - Shrinking HeatshrinkShrinking the heat shrink in place over the shielding remnants

Now that we have dealt with the shielding remnants, we need to get rid of the two data cables. USB cables for those prior to USB 3, use four conductors, two for power (the red and black), and two for data (green and white). Now whilst I could simply remove the cables by cutting them off I am too paranoid about shorting out the conductors and damaging the cable itself or worse one of the devices connected to the cable ends. To deal with this I trimmed the cables back short (about 4mm in length) and then folded them back over the heatshrink.

2015-01-12 - DC Cable - 18 - Conductor ColoursShowing the four USB conductors

2015-01-12 - DC Cable - 19 - Snipping Data CablesTrimming Data Cables

2015-01-12 - DC Cable - 20 - Folding Data CablesFolding the data conductors back over the heatshrink

Now I have the issue of holding them there, given my desire to do my utmost to prevent possible shorting and possible damage to devices I am going to heat shrink them down in place

2015-01-12 - DC Cable - 21 - Heatshrink SizeHeat Shrink cut to cover the Data Connectors 2015-01-12 - DC Cable - 22 - Heatshrink PlacementHeat shrink Over Conductors

Once this is in place and heat shrinked down the next step is to bare the other two conductors, and it is at this point I twist the strands of the conductor together and tin the conductors. Given how small the conductors are on my cable, I simply used my fingernails to strip the wires

2015-01-12 - DC Cable - 23 - Tinned WiresStripped and tinned connectors

It is then simply a matter of putting the conductors through the holes on the inner section of the DC plug, with the positive going to the tip and the negative going to the barrel, once they are soldered in place securely, trim the conductors as close as possible to the soldered joints, this is to minimise the interference when sliding and screwing the shroud into position.

2015-01-12 - DC Cable - 24 - Installed and Soldered ConductorsPositive and Negative conductors soldered in place

2015-01-12 - DC Cable - 25 - Trimmed ConductorsTrimmed Conductors

Once this is done, slide the shroud over the cable and you are done

2015-01-12 - DC Cable - 26 - CompleteCompleted cable

I have tested this cable on my Iridium 9555 and an Apple USB charger and it works fine, the charger gets warm as one would expect but no more warm than when charging any other phone. I have also tried in on other USB chargers and so far they have all worked fine.

Enjoy and as always do this at your own risk


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