Connecting a Telephone handset to a USB Sound Card

I have a bit of a thing for ruggedised telephones like the ones you see on railways and industrial settings. In the UK the main manufacture is Hubbel, formerly Gai Tronics, formely DAC...

Their phones cost a fortune new but occasionally pop up on EBay for reasonable prices, however they're usually in some state of disrepair and spare parts cost a fortune. £200 for a replacement handset for a £600 phone. Yikes! (Incidentally I suspect this is why the end up on EBay, it makes more sense to buy a new one than try to get spares)

For a long time I've wanted to create my own custom internal controller to replace any that are broken, with the added bonus of converting them to SIP. I had some concerns about interfacing the handset / reciever with a soundcard as telephones generally operate at a different impedance to your average speaker and microphone, so I connected one up as a proof of concept. 

I chucked a photo up on Twitter and it was suprisingly popular so I thought I'd document the process

New Teams Headset pic.twitter.com/lOA4McTV5f

— Matthew Harrold (@MatthewHarrold) July 29, 2021

BG7TBL 88-108MHz FM BPF Band Pass Filter

I've recently been listening to Pirate and "DX" FM Broadcast radio so I purchased a BG7TBL 88-108M FM BPF Band Pass Filter Ebay and stuck it on the NanoVNA to check it out.

It tested out well, with less than 2dB loss in the passband and 30dB rejection below 50MHz and above 145 MHz. Not much else to say about it, I'm just sharing here for posterity.

 

APC 940-0103 Pinout for AP9211 AP9212 AP9217 & AP9218

APC can get in the sea. Every one of their devices uses a random connector with an obscure pinout for the console port. RJ50, RJ11, 2.5mm Stereo Jack, male DB9, to name a few.

I recently aquired an AP9212 in a job lot and wanted put it to use but didn't know the network config so had to console in. Except the DB9 on the front was male, and my el cheapo USB to RS232 adapter was also male. Hmm. Anyway, some googling later I managed to find the correct pinout, which turns out is just a "normal" null modem cable

Bodging an RJ11/RJ12 Console Cable for use with an APC 7922 (And possibly others)

I recently aquired an APC 7922 Switched PDU - you can read more about it here

Unfortunatly when I aquired it the network interface wasn't working ( I suspect auto negotiation had been disabled) so I needed to console into it to get it factory reset and working.

Well, APC are a bunch of plonkers and tend to use odd connectors and pinouts on their console cables so you spend more money to aquire them. Well, I'm too smart  tight for that, so I looked into making my own with bits I had around the house. After a trip to the parts boxes I returned with an old Cisco Console Cable and some RJ12 connectors and just needed to figure out the required pinout.

After a bit of tweaking I mangaged to get something functional made up 

 

Upgrading the Firmware on an APC 7922 Switched PDU with FTP

I recently aquired an APC 7922 Switched PDU as part of a bulk purchase. Its a chonky box that sits in the rack at a data centre and distributes power to servers, switches and routers etc much like a 16 gang extension lead but it allows you to remotely switch devices on and off, monitor their power usage, and do things like add delays to devices powering up when the power is restored - useful for managinging in-rush current.

Whilst it's a nice bit of kit its not particuarily useful to me, especially give that the sockets are IEC13, so I thought I'd stick it on eBay where it could still get £100+ despite it being relatively long in the tooth. 

Before I listed it I thought I'd do some house keeping - Factory reseting it, testing it worked, getting the firmware up-to-date and finally it was just an excuse to play with it as it has been several years since I worked with this kind of gear.

The following blog post should help you get an APC 7922 upgraded to the latest firmware using FTP. Why FTP? I hear you ask. Well, I can't SCP it because it uses some ancient SSH implementation that wont play ball, and I couldn't find anywhere to download the "Firmware Upgrade Utility" - so FTP it is.

 

Return of the Cisco 887VA - Testing and updated config

 Around 3 years ago I blogged about using a Cisco 887VA Router as a VDSL Modem.  As far as I recall I actually documented the configuration whilst getting ready to sell it, as I was downsizing my network.

Well, my network has since creeped back up in both size and complexity so I wanted to swap out the venerable Huawei HG612 VDSL modem for something else that could be rack mounted (cos bling). A quick google suggested the Cisco 887VA was still a good way to go, so I purchased another.

Resetting the password on a Cisco Catalyst 2940 Switch - (Hint: It doesn't involve sending a break)

I recently got frustrated with the crappy "smart" switches in my network so I replaced them with second-hand Cisco hardware. Because no one got fired for buying Cisco, right? 

It turns out I don't need 1Gb/s to things like VoIP phones and my Blu Ray player, so I could get away with older models with 100Mb/s ports and a single 1Gb/s uplink, like the WS-C2940-8TT-S which are available for £25 and fan-less, with something beefier as the "core".

Whilst I was getting it configured I figured I should probably have a go at performing the password reset. For some reason I had it stuck in my head this entailed sending a break signal whilst it was booting to get into ROMMON, and then changing the configuration-register to ignore the config stored in the NVRAM when it booted. After desperately sending break signals, swapping console cables and generally swearing at the thing I got around to RTFM and realised I was doing it wrong... it seems the whole break into ROMMON thing is the procedure for another router I own, but not the Cisco 2940. Doh!

There's 1000s of guides on resetting Cisco switches. I'm mostly just writing this to commit it to memory and so I can look back on it next time I waste an hour send break signals to a switch.