BT Response 150

Introduction

Yes, this is just an old wonderfully-yellowed landline phone, so lets keep this short. This particular item is from week 5 of 1995, and the full specifications of it can be found on britishtelephones.com. What I am more interested in, is what's inside - how does it work, how was it designed.

Exterior

Powered from a 9V 500mA AC adapter, it (unsurprisingly) has a handset and base station, which are connected via the standard coiled cable. The top-side has some standard buttons for the answer phone, time, and a power and message indicator. However, more interestingly (to me at least), under a cover, it has a microcassette. Understandably, this is just for a pre-recorded message to be played if the phone is not answered, but I didn't know these existed - and they're rather cute.

Along with some switches and buttons to control how this all works, there is a mini user guide on the underside of the cover. Looking at the underside of the base station, it has holes for the ringer speaker, of which can be adjusted in volume with a switch on the back providing the options "Hi/Lo/Off" (High, low or off).

Disassembly

Starting with the main unit, there is a mainboard attached to the bottom-side, and a series of ribbon cables and connectors leading to the various boards and components in the top-side of the case. Given all the contours and different functions, there are quite a few different boards.

The main board is another one-sided PCB, with plenty of jumper wires around. There are expected components like op-amps, optocouplers, ICs that can't be found on the internet, along with the usual passives. The top-side houses three different boards - for the front buttons, the microcassette mechanism, and the answer phone controls. In addition, a speaker is position here but I am confused - I would have thought this is the ringer speaker, however, it is directed towards the hard plastic immediately below where the handset is placed. The speaker ringer holes, I mentioned earlier, are positioned on the underside of the mainboard, on the opposite side to this speaker. I don't know as I've made an incorrect assumption as I never removed the mainboard to see underneath, as there could be a different component or another speaker there instead. Either way, it should work, but this mystery will probably haunt me for a while, as I doubt I'll get around to opening it again anytime soon. Lets move on.

The handset continues the trend of layered boards but seemingly to cater for the curve of the device. Here, there are two PCBs stacked immediately on top of each other via screws and standoffs with a very not discrete ribbon cable between them. The lower board is a two-sided with vias to accommodate for the large IC package that I'm assuming is the controller for the membrane buttons. The main IC in the middle of the top board is a TEA1064AT "Low voltage versatile telephone transmission circuit with dialler interface and transmit level dynamic limiting" - basically does all the speech and line stuff for a telephone set to work.

Obviously, there is also a microphone and speaker which have been beautifully jumper-wired onto the one-layer board, but that's about it.

Closing Thoughts

It's a phone, it does phone things, or I should probably say "did" - I have no idea if it still works as we don't have a landline anymore. It was produced, used, discontinued, and probably stopped being used before I was alive, so oh well.