History

Disclaimer #2: With the demise of the Public payphone, BT have extensively converted a lot of them to "No-Cash Calls" by removing the coin handling and validation mechanism. Consequently, if you acquire a second-hand unit, the chances are you might only be able to use it for Free (e.g. 0800 etc.) calls only.

The CT54 appears to essentially be the upgraded version of the older type CT24A Payphone (BT Payphone 600). The easiest way to distinguish between the two is to look at the handset. The CT54 can be identified by its square style handset whilst the earlier CT24 has a rounded handset. In addition to this, the CT54 has an upgraded Dot-matrix style LCD screen whilst its older counterpart has a fixed-segment display. Whilst the handset is on-hook, the CT54 display will constantly cycle between the words "BT PAYPHONES" and "TO CALL LIFT HANDSET". (Unfortunately the letter 'H' of both phrases happens to be displayed in exactly the same place on the screen and so it's not surprising if some screens suffer from some form of image-persistence ("burn-in").

The remainder of the differences between the CT24 and CT54 are to be found within the body of the Payphone itself. Whereas the CT24 relied on the supply of meter pulses from the local exchange for call-timing and billing purposes, the CT54 is essentially a standalone Payphone that maintains a local copy of the current tariff table. Presumably this was due to the withdrawal of the Meter Pulse Facility (MPF) on the BT network between 30-Mar-2007 and 01-Sep-2008.

Other key differences include the replacement of the pluggable internal Ni-cad battery found within the CT24 with a much smaller, 'supercapacitor' that is soldered directly to the PCB of the CT54. This presumably significantly reduces the on-going Payphone maintenance costs associated with the CT24. The overall footprint of the electronics within the CT54 have been drastically reduced in size. The CT24 PCB completely filled the rear panel of the case and used older-style through-hole components. The CT54 comprises two separate PCB's; a smaller "Interface" board that contains the tone caller, interface sockets and line/power filters. This connects via a 96-way DIN-41612 connector to the larger "Digital" or "CPU" board that contains the remainder of the digital electronics such as CPU, RAM, Modem and Telephony components. These are all Surface Mounted Devices (SMD's) and enable the PCB footprint to be reduced to a mere 10cm x 20cm.