These pages record my investigations into the technical detail, engineering practice and social history of the optical phone card in Britain.
One of the Card Phones on display at Avoncroft Museum
From "Focus" July 1981
What's new about payphones ?Have you ever walked into a public payphone only to find there are no 5p or 10p coins in your pocket or handbag? Or found a foreign coin (or even a mutilated British one) jammed in the slot? Or discovered that the whole system has been vandalised during an attempt by petty thieves to make off with the coin box ?
On display at the ideal home exhibition this year, and attracting a lot of attention, was our new entry in the Payphone range the Cardphone, which could help to overcome these sorts of problems.
About 200 of these press-button Cardphones are currently on trial in London, Birmingham,Manchester and Glasgow, in busy places like airports, main-line railway stations and city centres.
Sited near ordinary Payphones, to give our customers a choice, they are suitable for inland and all overseas calls currently available on IDD.
To use the new phones, customers will need to obtain special cards which are similar in shape
Apart from being less attractive to criminals Cardphones also bring these benefits:
Cards are a convenient light-weight alternative
They avoid the need for "feeding" the phone on long distance calls;
They enable us to make savings by removing the need for regular visits to collect or clear jammed coins.
Cardphones are also easier to use and because they are microprocessor controlled they can be programmed to enable calls to certain numbers - such as 999 emergency calls - to be made without a card.
A visual display on the phone indicates how many unused units are available, on the inserted card
During the trial it is proposed to make the cards available from various places in the areas where the Cardphones are installed. These will include newsagents and tobacconists as well as Telephone shops and Post offices.
If these trials show the Cardphone to be popular we will consider the possibility of installing more in town locations,so brining the cashless society one step closer.
There are excellent technical articles form Landis & Gyr here ..
The above article says there are upto 120 bits stored per track, ie 240 bits on a reversible card.
At the start of the track are type bits, then come the value bits - possibly 20 type bits then upto 100 value bits (units)
Every (value?) bit on the card is encoded with a holographic family code, which the reader rejects if its not the correct family code.
It looks like each family code has a different hologram( or structure, eg STU7 for uk cards), light is projected onto the correct bit on the card, two light sensors at different angles measure how much light I reflected. If the light levels match the correct family code the bit is counted as valid.
Some of the type bits are erased when the card is exhausted, presumably this makes reading the value of an empty card quicker ?
bits are erased by applying heat to the front of the card until the family code stops being read by the sensors thus proving erase has been successful.
Says that a card track has 1 Sync bit, 7 type bits and 120 value bits - a total of 128 bits per track.
type bits ---------- value bits--------------------------
"To check the validity of the information carries by the value units, they are illuminated by a beam of infra read radiation. This is reflected at certain angles depending on the chosen micro structure and checked by appropriate detectors."
The electrical signal is then amplified with these Texas Instruments TL062IP LOW-POWER JFET-INPUT OPERATIONAL AMPLIFIERS
and converted into digital domain
for evaluation by the microprocessor
To the naked eye the back of the phone card just looks shiny black
but under infra red light with an infra red camera .....
The tracks can be seen from the back of the card, with the hologram dark and shiny
I've taken close up of the type bits on different cards..
The left most bit of the right hand block seems to have a different hologram the the rest of the block, perhaps it is the "sync" bit ? BT TPU 1030 describes it as the mirror but, which is followed by a 5/8 width start but, then four out of seven
test card 100 units
There is a lot of possibly unnecessary maths in this article.