CT22A Blue Payphone AZ33

Coin Telephone 22A - 3 coin slots and red LED display
Autelca AG 3073 Gumligen Schweiz
Typ 386 0889 Dat 12 Nov 1980 L.Nr. 000390

temple meads pay phones

They're new they're blue
Electronic pushbutton payphones - with a microprocessor which works out the cost of the call and returns any unused coins - are currently on trial at some busy payphone sites,ranging from places like Dover docks to Glasgow Airport. A hundred of these new phones have been purchased as the first step in re-equipping our coin-box telephones.
These electronic payphones have a number of attractions for both us and our customers:
• the microprocessor acts as an electronic `watchdog', being programmed to call up repair staff automatically if a major fault has occurred;
• their pushbuttons are easier to use than a dial;
• customers will be able to make direct calls from them to all 89 countries on international direct dialling with the UK;
• they will be easier to install; the built-in microprocessor eliminates the need for special call-charging equipment at the local telephone exchange, unlike the present dial payphones; and the current tariff inflexibility, which necessitates a single coin minimum fee, can now be overcome.

To use these new payphones, customers put money in before keying the number. There is no pay-tone as with ordinary 'pay-on answer' payphones.The coins are held in store as a credit and the amount is shown on an illuminated display. During the progress of the call, the amount displayed diminishes as the credit runs down. The rate at which this run-down occurs depends, of course, on the distance and time of day. The microprocessor works out the rate from meter signals received from the local exchange - in the same way that ordinary phone lines are metered.

A warning is usually given ten seconds before the credit finally runs out, with a display request to insert more money. There is also an audible `bleep' on the line. The phone is then automatically disconnected unless more money is inserted. Users can put in more coins at any time during the call. At the end of the call, the phone - under instruction from its microprocessor - takes the coins it needs to pay for the call. Any whole unused coins are returned to the Customer. Alternatively, by pressing a 'follow-on' button, further calls can be made using credit held over from the previous one. At the places where the phones
are being installed for the trial, travellers often need to make long-distance calls - either over seas or within the UK. For greater convenience in making these calls the new phones will take three denominations of coins, including 50p pieces. Users will, of course, be able to make operator calls - restricted to inland initially - from the new payphones. On such calls, a`bleep' is heard as a background signal to tell the operator that the caller is using one of the new payphones. These electronic payphones have stainless steel cases, with the instructions on them printed in blue. Signs, are also in blue, and hence the new coin telephone is known as the 'Blue Payphone'. Instructions posted inside the kiosks explain how the new phones arc used.
During the trial, we shall be carrying out customer research, asking users their opinions of the new phones. We will also be checking on the use people make of the new phones compared to ordinary payphones nearby. The trials are proceeding satisfactorily at present, and plans are in hand to replace 17,000 public call office (PCO) sites, which take more than £1,200 per annum, with these new payphones. There are Currently 77200 PCO sites which are due for replacement under the re equipment programme to be completed by 1990. Most of these will be replaced by a cost reduced, modified version of the blue Payphone, which will use more up-to-date technology, but some 1700 will be replaced by a new debit-card phone, which as its name implies will be coinless.

New payphones take the credit

L L Grey - PO Telecommunications Journal, Autumn 1979
New style microprocessor-controlled payphones incorporating a sophisticated new range of facilities are soon to
be installed on a trial basis mainly at high revenue public call office (PCO) sites throughout the UK.

THERE CAN hardly be a single telephone user who would not like to see Pay On Answer (POA) telephones quickly phased out. Their fault record, their inability to make certain international calls, the need to stack up coins when making expensive calls and the interruption to speech when coins are inserted, are all features which have caused much irritation over the years. And as far as the Business itself is concerned, the tariff inflexibility, which necessitates a single coin minimum fee, is not popular.
Steps are being taken, therefore, to replace POA and the first move is to re-equip the 16,000 public call office (Pco) sites which take more than £1,000 a year. In all there are currently 77,600 Pcos.

During the autumn the Post Office began to take delivery of a trial quantity of 100 self-contained microprocessor-controlled coin telephones designated 'Az33' by the Anglo/Swiss manufacturer, Agitelco, of Croydon. The model will be known as the Blue Payphone - it has blue directional signs and user instructions - to help the public recognise it and as a means of reference between customers and operators in operator assisted calls. The new coin telephones are being installed at Heathrow, Victoria Station, Trafalgar Square, Birmingham New St Station, Gatwick, Cardiff Airport, Glasgow Airport, Edinburgh, Manchester (Ringway), Dover Docks, St Paul's and Liverpool Street Station (with a further 10 on selected renters sites.)
The Blue Payphone is self-contained in that all the essential operating equipment, including the coin and fee check function, is contained within the coin telephone itself. It accepts 2p, 10p and 50p coins at the beginning of a call and can hold a total of about £3 Right maximum credit displayed on 7 segment LED display
if required until 'cashing-up' takes place at the end of a call (or series of calls). It has a four-digit light emitting diode (LED) credit display to show the value of credit remaining throughout the progress of automatic calls and a follow-on call button to enable the customer to make a series of calls for a single payment without replacing the handset. It also has full International Direct Dialling (IDD) capability. The az33 is connected to an ordinary exchange line via a subscribers private

Senior Technician Ray Guntripp, from LTR West Area sizes up an A233, soon to be fitted at Heathrow Airport's Terminal 2. Lending a hand in the foreground is colleague Brian Dare.

metering (DPM) relay set in the local exchange and its tariffs therefore are basically linked to ordinary subscriber tariffs rather than coinbox tariffs.
Introduction of the equipment into service marks the culmination of three years of work undertaken initially by a small THQ team but, since the contract was placed in December last year, by a full THQ project team which has wrestled with the managerial, technical and personnel problems connected with the introduction of this sophisticated new equipment.
Unlike POA which employs direct coin collection by collecting money first and then putting paid time at the user's disposal, the Blue Payphone employs indirect collection by offering conversation time corresponding to the amount of money inserted. On completion of the calls, only those coins needed to meet the accrued charges are collected - starting with the highest value coin which has been spent.
Perhaps the most remarkable achievement in the UK version of the Swiss nz coin telephone is the inclusion in the software program of the

Making final checks before the new payphone leaves the workshop is Inspector Terry Parker.

full range of operator services available to ordinary subscribers lines. To the customer the making of operator assisted calls is basically no different from POA. Non-chargeable calls are obtained by keying 142, 151 and so on in the normal way. In the case of chargeable calls, the operator, who will recognise the Blue Payphone due to the presence of a special identification tone, will ask the customer to insert money when the called subscriber answers. This money will pass straight into the cash box - unlike the procedure for automatic calls. Should the customer insert money immediately on lifting the handset and then key any three-digit operator code, the coins will be refunded after the last digit has been keyed.

It is possible to follow an automatic call by a chargeable (or non-chargeable) operator control call after using the follow-on call button. In such a case, coins inserted for the original automatic call are held in the coin store with the display showing credit remaining from the automatic call. Additional payment is made for the chargeable operator-assisted call as requested by the operator. When the customer finally replaces the handset the equipment will cash up for all automatic calls made, in the normal way. In other words, when the follow-on-button has been used, payment for automatic and chargeable operator connected calls are treated as separate cash transactions.
There is, of course, a price to be paid for such flexibility in meeting Business needs for both automatic and operator-assisted calls. In fact, between one quarter and one third of the microprocessor memory
- total capacity 4k bytes - has had to be used for this purpose at the expense of self-diagnostic facilities which the az33 is capable of providing. In the field trial only, a second telephone pair is being specially provided to carry automatic diagnostic reports to the repair service centre. These reports will be limited to notifying a full cash container which would put the coin telephone out of action for paid calls or a coin checker/ mains failure fault. The Az33 is how ever designed to need not more than three maintenance visits a year - excluding vandalism.
Processor Memory Chips

There are a number of technical advances in the Az33 design. Coin validation is a crucial feature of any coin telephone and in this case, coins are subjected both to physical and electronic checks.
By virtue of its self contained design segregated coin telephone lines are no longer required and this will permit greater flexibility in exchange planning and eventually enable non coin and fee checking equipment to be removed once full production of self-contained payphones is under way. Tariff changes are effected simply by changing a coded plug in the control unit.
The coin telephone is mains powered. If there is a mains failure while the equipment is in use it will retain any money due until power is restored and return unused coins to the refund chute immediately. The 999 emergency service only will continue to be available during mains failure.

The cash compartment contains a 2.6 litre cash container with a self locking mechanism which closes the coin aperture immediately the container is removed. Once this has been emptied in the coin counting centre, and before being replaced inside the coin telephone, it is necessary to re-set the self-locking mechanism inside the lid of the container. A coin meter, registering 1p units, is fixed to the cash compartment door and this is read each time the container is removed so that an accurate record of cash takings can be maintained. It is likely that these will be considerably in excess of POA equipment being replaced.
The field trial Blue Payphones will normally be recognisable by a blue sign over the kiosk bearing the words `Intercontinental and Inland' to distinguish them from POA phones. When all the trial sites are operational more than 3,000 operators accepting calls from the trial sites will have been trained and 20 fitters and 30 maintenance staff will have undergone training at RETC Bletchley. About 12 presentations will also have been given to COPOU, and its constituent bodies, and to Regions and Areas taking part.
There will, of course, be the inevitable teething problems in launching the field trial. But once this has been completed, by mid-1980, the intention is to place s, full production order and complete re-equipment of high revenue Pcos within about five years. Simultaneously, a separate pro¬gramme has been initiated for a medium/low revenue coin telephone which would be slightly less sophisticated than the high revenue variety and possibly quicker to produce.
At the same time, an in-depth study has examined the practical problems involved in providing public telephone service from equipment operated by pre-paid debit cards in lieu of coins to back-up - but not replace - coin-operated pay-phones. When the result of this study is to hand, together with a parallel study of technical possibilities, the Post Office will be in a position to decide when to begin and get some practical experience in the use of card phones as the third prong in the attack on the re-equipment of public call offices.

Mr L. L. Grey is a Head of Section in the Residential and Customer Service Department and is Project Manager for the AZ33.
Extract from Maintenance News 18, Spring 1981
front cover of Maintenance news 18 spring 1081
Thanks to Sam for scanning this booklet

Maintenance thoughts on new coin boxes
by Maurice Bradley LTR/SV4.3.1 
Most people are  aware that a  new generation of microprocessor controlled payphones will be progressively replacing the pay-on-answer ( POA) boxes. But  few  of those  who have been involved with the maintenance of electro-mechanical  POA boxes will  mourn their passing. 
For  introductory purposes. the  new range of payphones  are  divided  into three  tiers. 
  • Tier 1  is  the  Blue Payphone, a  name  most of us are  now familiar  with. For  engineers it  is  more correctly coded Coin Telephone 22A (CT22A)  and on trial now. A production model to follow will  be coded CT22B.  Both are  primarily for  high revenue sites. 
  • Tier 2  is  a  re-designed.  cheaper version  of Tier 1, and will  be used for  ordinary public call  offices (PCOs)  and renters installations. 
  • Tier 3  is  a  portable, table-top  instrument with reduced facilities  compared with Tier 1  and 2  -Ideal for  hotels, restaurants  and similar establishments. 
Another item  in the  new range  is  the Debit  Card Payphone -Intended  to accept specially designed  credit  cards. 

Tier 1  and the  Debit  Card Payphone are powered from  external supplies whereas Tiers  2  and 3  will  be powered from  the telephone line.  All require  the  services of Subscriber's Private Meter (SPM) equipment at the  exchange but  dispense 
with the  need  for  a  Coin and  Fee  Checking  (CFC) relay  set. 

The approach  to fault  finding  and clearance is  going  to be very different from the  POA coin box. Instead  of coin acceptors, pulser units.  runways and so on, the  faultsman's  language  will  be Central Processor Units  (CPU).  Speech  and Interface  (S and I)  boards.  Power Supply Units  (PSU).  credit displays,  edge connectors  and the  like.  Faultsmen will  have a  diagnostic kit to help them  and, by using the  diagnostic testing  facilities  built-In  the CT22. they will  be able to approach  their task in a  truly  professional manner. 

Care necessary 
The recommended methods of handling this equipment- particularly  the  printed Circuit boards- are  different from  the accustomed practices  of faultsmen.  For example circuit boards  with edge connectors  must be extracted  and  Inserted only when  absolutely necessary. They  must be handled with extreme care,  always carried  in anti-static bags,  and  provided  with adequate  protective covering. 
In time faultsmen will  need  to become expert in the  facilities,  and  capable of recognising  the  causes  of the  more common types  of failure.  This equipment should  help create pride  in the  work,  which most found difficult when  working with POA apparatus. 

Faultsmen will  still  meet all the  old situations and conditions that do little  to help thier task - kiosk  windows broken  or 
missing, customers anxious to use  the  box being  worked  on,  noisy  railway  stations, bustling airport buildings ·-and  many  others. This is an exciting challenge which faultsmen will  be facing  if  British Telecom is  to seize  this opportunity  to provide  the  type of PCO service  the  public demand. A  first class  maintenance effort  is  necessary even though  these  processor-controlled payphones  are  remarkably  advanced machines. They  must not  be taken  for granted. After working on a  box. a  faultsman must run  though the facility test  schedule and  satisfy himself  that all is  as it  should  be. This includes  a  check to ensure that both the ear and mouthpieces are  correctly fastened  with rivets. 

Another point  to remember is  that most members of the  public will initially find the new PCOs  very strange  and some  may not be able to understand  the  instructions. Maintenance staff may be called upon  by frustrated customers to explain, and  this should  be done  in a  way that will  inspire confidence.  No doubt some  customers will expect to get coins  refunded  when  they  are not  entitled  to them. But  the  new call  office mechanism does  not  give change, it  only returns  those  coins  not  used during the  call. For  example,  if  a  user puts one 50p piece into store,  makes a  call  to the  value  of 10p, then  hangs up,  the  machine will  claim  the whole of the  50p. But  if  at the  end of the  caII. and before hanging up,  the  user inserts  a further  10p piece, the  payphone will  claim the  10p piece  and return the  50p to the  user when  the  handset is  replaced.

Points to remember  
Maintenance staff need  to fully understand
  • Payphone facilities 
  • Methods of fauIt diagnosis - using  the diagnostic  kit when  necessary 
  • Correct  handling of electronic printed circuit boards  (PCBs)- both and out  of the  machine. 

There will  be much  for  faultsman to learn during the early days of the  new equipment. It  will  be very important  when  new problems or difficulties are  found that help should  be sought.  They  should  also pass on promptly the  lessons  which have been  learned  to the right  people.  Engineering groups  at RHQ and THQ will  be keen  to give help and  information to field  staff to resolve  problems  as they  arise. Developments in public call  offices will give British Telecom a  good  opportunity  to improve the  public image of this important service- at the  same  time  giving staff the chance  to work with equipment using present  day technology. 
01-587 7038



TELECOMMUNICATIONS INSTRUCTION                                                                                  E5C 3101



Coin Telephone No 22A


Description and Operation

Index to contents:

1 Introduction

2 General

3 Physical details

4 Operation



1 Introduction

This instruction describes the CoinTelephone No 22A and outlines its facilities, 100 of these cointelephones have been purchased for field trial in selected Areas. These are pre-production models and some changes will be incorporated if further quantities are purchased.


Further information relating to the CT 22A is contained in


E5C 3102        On-site Maintenance Instructions

E5C 3103        Maintenance, Center Attention

C3G 7051        Installation Instructions



2 General


The Coin Telephone No 22A is a self-contained, mains powered, prepayment unit intended for use on high revenue sites particularly where there is a large element of continental and intercontinental traffic.It offers facilities suitable for IDD, STD and local calls and accepts 2p, 10p and 50p coins. The instrument incorporates a keypad and credit display. Full operator access is available. Figures 1 and 2 illustrate the description in the following paragraphs.


3 Detailed description


3.1 Casework

The case is constructed of stainless steel.           The dimensions are:


Height 540 mm Width   280 mm Depth 290 mm. Weight           36.5 kg


The casework design offers a high degree of security against unauthorized entry. The upper, mechanism, compartment has a door hinged on the left and secured on the right by a good quality lock operating a bolt system. The lower, cash compartment has a drop door secured by a similar lock and bolt system.


3.2 The coinbox is secured to a mounting frame by bolts which are accessible only from inside the cash compartment and mechanism compartment. The mounting frame is fixed by bolts which can only be reached when the coinbox has been dismounted.


Mounting frame showing 6 way contact strip

3.3 Connections to the box are via a 6-way terminal/contact strip in the center of the mounting frame. A 6-way contact strip on the back of the coinbox picks up the connections automatically when the box is hung on the mounting frame.The earth connection is to the mounting frame and is extended to the box via the bolts which secure the box to the frame. (Figs 3 & 4)


3.4 The handset is supported in the pendant position on a forked gravity switch hook on the left of the box. A standard PO handset No 11 is used but the plastic cord is replaced by flexible conductors in a flexible stainless steel sheath anchored securely to the handset and gravity switch assembly.


3.5 The gravity switch hook assembly carries a follow-on call button on the front face which in obscured by the handset when it in on-hook. All components of the assembly are readily interchangeable after removal of a plate on the rear of the assembly. The whole assembly is secured to the case by a spigot which passes through a heavy steel collar on the inside of the case. Rotation of the collar clamps the spigot with a powerful cm action. Connections from the gravity switch hook assembly are by means of plug ended card*.


3.6 The mechanism compartment door carries a sloping, protruding console which houses the keypad, credit display and bell and contains three windows for instructional displays, credit display and exchange number label in that order from top to bottom.


3.7 The keypad has ten buttons and, on the trial version of the coinbox, in of standard construction with plastics buttons and button matrix,


3.8 The credit display is of the 7 segment, LED type with four 0.3 inch high digits providing for amounts between 00.00 and 99.99. The decimal point is us

ed as a 'power on' function indicator for the box. The PWB at the rear of the display unit carries the logic for the unit and the clusters of filament lamps which illuminate the two user instruction displays in the upper display panel.


3.9 The user instruction displays consists of an 'INSERT MONEY' legend

in the left hand half and '9990NLY' legend on the right. They are invisible until illuminated from the rear, (Note: on the trial boxes the 999ONLY legend is not used.) Connections are via plug ended ribbon cable.


3.10 The bell is a single coil, single gong unit fixed by two screws and connected by plug ended cable. A friction device permits adjustment of the eccentric gong without loosening the center fixing screw.

3.11 The exchange number label is a self-adhesive slip inserted from the inside of the owe by removal of the credit display unit (3 screws).


3.12 All display windows are of tough, laminated glass. Access to all the sub units in the console requires removal of the complete coin checker assembly, ( 4 screws.)


3.13 Coin checker assembly. This comprises a back plate, which carries :-

(a)    the coin entry plate with closure shutter and its operating solenoid

(b)   the test flap operating solenoid and common slide bar.

(c)    the accept solenoid and common slide bar.

(d)   the three coin checkers.

(e)    the solenoid driver PWB.


Each coin checker is individually removable by undoing a knurled thumbscrew and withdrawing from a support pin. When in place the coin checker accept and test flaps are operated on all three coin checkers simultaneously by the solenoids and slide bars.

The 3 coin Checkers 

3.14 Each coin checker is based on a moulding in a wear resistant, low friction, plastics material. The moulding, in cooperation with a hinged test flap, provides a coin entry and testing channel which gives access to either a reject channel or storage channel in the lower portion of the moulding. Rejected coins pass straight through the reject channel and are returned to the customer. Accepted coins pass into the storage channel and are either cashed under the control of a cashing electromagnet or refunded on operation of the refund electromagnet. each coinchecker carries a PWB containing the control and drive circuitry for the electromagnets and the circuitry for carrying out a materials check on each coin.


3.15 Connections to all three coin checkers and to the solenoid driver PWB is by means of a connection PWB carrying appropriate connection sockets and plug ended ribbon cable.


3.16 The microprocessor PWB and Speech and Interface(S&I) PWB are carried in a pivoting frame in the main case of the box. The frame locks in both closed and open positions and must be lifted before it can be moved. The PWB's slide in guides and edge connection strips engage with socket connectors on the frame. Each PWB carries two card ejectors to facilitate withdrawal of the card from its connection socket. Replacement of a board requires only that the board is slid into its guides and firmly pressed home in the connector by pressure on the ejector. The cards are keyed and cannot be interchanged. The microprocessor PWB carries the processor and associated logic, accounting and timing components. The S&I PWB carries the telephone speech circuit, alarm circuitry, meter pulse receiver and the components which enable the processor to monitor the circuit conditions which arise during the operation of the box and to implement its control signals.


The microprocessor PWB

Speech and Interface(S&I) PWB

3.17 The Power Supply Unit (PSU) is mounted in the main case below the main PWB's. It is by far the bluest part of the "blue" payphone.

Input to the PSU is at 24v ac or do and the box is thus completely safe for users.PSU outputs are:


24v dc for solenoid operation

15v dc for microprocessor and logic

5v do for credit display and instruction indicator lamps 5v do for mains failure refund logic.


The Power Supply Unit

34,000 micro farads of smoothing/storage capacitors are sufficient to bridge power input interruptions of up to 1 second duration without impairing the function of the box. In the event of a longer break there is sufficient stored power available to refund unused credit to the user and release the call. Coins in store representing used credit are held in store and not cashed until power is restored.


3.18 Power consumption of the CT 22A varies from 4.8 w when the box is quiescent to a peak load of 36 w during solenoid operation.


3.19 The 24v ac supply to the box is normally provided by an independent 240/24v step down transformer.


3,20 Tariff setting is determined by a pre-programmed, plug-in unit on the microprocessor PWB. A tariff change entails replacement of the plug-in unit.


3.21 The cash compartment cover carries the refund cup which is provided with two hinged flaps. The outer flap is of clear plastics material which allows customers to see coins lying in the bottom of the cup. To reach the coins the flap has to be pushed backwards and in this position the flap closes the aperture via which coins reach the cup from the upper compartment. To provide additional security against unauthorised access to the mechanism compartment -a second, stainless steel, flap normally closes the aperture from the mechanism compartment under the tension of a light spring. The weight of a coin is sufficient to depress this flap to allow the coin to drop into the cup.


3.22 The cash container content meter is mounted on the right hand side of the cash compartment cover. This meter registers the total value of coins falling into the cash container. The meter is sealed.

 The Meter

3.3 At the rear of the cash compartment is a rod protruding forwards which, when the cash container is inserted, opens the container coin entry shutter and holds it open whilst the cash container remains in position. Removal of the cash container releases the shutter to seal the container. After this, the container cannot be re-inserted until it has been unlocked and the shutter mechanism has been reset from within.


3.24 The cash container is of stainless steel construction and has a volume of 2.6 litres. It incorporates a coin level detector which, when the container is full, conditions the coinbox control circuitry so that further coins inserted are returned to the customer. In this condition only non-chargeable calls can be made.


3.25 A cash container presence detector in incorporated in the cash compartment. This also ensures that unless a cash container is in situ only non-chargeable calls can be made.


4 Operation


4.1 The operation of the CT 22A is controlled by a microprocessor. All functions in the box are operated, directly or indirectly, by signals generated by the processor and all functional elements generate signals which are fed to the processor to enable it to monitor their status. The processor responds to signals fed into it in accordance with a predetermined programme which covers all possible conditions and sequences of operation.


4.2 Automatically connected call.

The user lifts the handset, the gravity switch operates and signals the processor which

  1. Operates the cashing electro magnets on the coincheckers until all coins present in the storage channels have been cashed
  2. Lights the credit display to read 00.00
  3. Flashes the credit display until the minimum call fee has been inserted.
  4. Connects the calling loop via the telephone speech circuit to line


4.2.1 As the user inserts coins they are validated by the coincheckers and either taken into the storage channel(s) or rejected. Each valid coin's value is registered in the processor's memory. When the minimum call fee has been recognised the processor causes the credit display to stop flashing and turns off the 'INSERT MONEY' sign. It also removes the inhibition on the keypad which permits only 3 digit numbers to be keyed.


4.2.2 Provided that the exchange has returned dial tone the user may then key the required number. Each key depression is signalled to the processor which stores them sequentially in the memory. As, soon as any keyed information arrives into the memory the processor then proceeds to transmit it, in the form of standard loop/disconnect impulses, to the exchange. The timing of the pulses in under the control of the processor and a crystal clock which is used as the time base for all functions of the box.


4.2.3 After all keyed-in information has been sent to the exchange call routing and connection is performed by the exchange in the normal manner, ringing tons is fed back to the user.


4.2.4 When the called subscriber answers the Subs Private Metering Relay Set (SPM) in the exchange feeds a meter pulse out to the coinbox in the form of a balanced 50 hz signal on both legs of the line, to earth. The Meter pulse receiver in the coinbox recognises this signal and signals the processor which records the event in the memory and starts timing the interval to receipt of the next pulse. The processor also decreases the reading on the credit display by the minimum call fee. Conversation may now proceed.


4.2.6 When the second meter pulse is received the event is recorded and the time interval between it and the first pulse is noted. This interval identifies the charge rate in use on the call which has been made.


4.2.7    The coinbox is connected to ordinary subscribers meter feeds but


(a) in order to give exact value for money the call timing has to be related to the value of the minimum coin which can be inserted.


(b) a call charge rate rather higher than that appropriate to a ordinary subscriber has to be levied to cover the additional cost of providing and maintaining the call office.


Thus, based on the exchange meter pulse rate, the coinbox starts to generate debit pulses timed by its own clock which it uses in place of the meter pulses to control the timing of the call.


4.2.8 Ten seconds before credit is due to expire (as timed by the internal clock, ) the processor injects 5 pips of 400 hz tone into the speech circuit, starts to flash the credit display and lights the 'INSERT MONEY' sign.


If money is inserted these signals stop, the value of the money inserted is added to the credit display and the call continues.


If money is not inserted the processor disconnects the call as soon as the time paid for has expired.

NOTE The foregoing paragraphs 4.2 - 4.2.8 have been set out to illustrate the role played by the processor in controlling the operation of the coinbox. From here on the detail of processor intervention will be omitted and only the effective information described.


4.3 On any call, if the user wishes he may terminate the call by pressing the follow-on call button. This will cause the exchange connection to be released but will not initiate the cashing-up procedure. On release of the button dialling tone will be received and the remaining credit, (provided that it is above the minimum call fee,) may be used to make further calls.


4.4 When the handset is replaced the call in progress will be terminated and the cashing-up procedure will take place. The box will automatically cash into the cash container coins to cover the value of the call which has been made and will return coins in excess of this value to the user. The box will take the minimum value from the coins in store which will cover the cost of the call. This is referred to as 'Best deal accounting'.


4.5 If 1 x 50p coin, 2 x 10p coins and 4x2p coins have been inserted - which will be shown on the credit display as 00.78p - and the cost of the call made is 26p, the box will cash the two 10p coins and three 2p coins and will refund the remainder. If the cost had been 52p the 50pcoin and one 2p will be taken, and the rest will be refunded.


4.6 If a single 50p coin has been inserted and the cost of the call(s) made amounts to, say 22p, if the handset is replaced at the end of the call the box will be forced to take the 50p coin. However, by terminating the call with the follow-on call button the user will then have the opportunity to insert smaller coins to the value of  22p so that when he replaces the handset the box will cash the 22p and return the 50p coin.


4.7 Incoming calls may be received by the box. When such a call is received an identity tone consisting of alternate pips of 800 and 1200 hz tone will be connected to the speech circuit for a period of 10 seconds. This will enable a distant operator to recognise that the call is to a coinbox and, if a reverse charge call is required, she will be able to collect money from the coinbox user taking the call before connecting.


4.8 Outgoing operator controlled calls.


4.8.1 Three digit codes may be keyed without insertion of money. After the 3rd digit has been keyed the credit display stops flashing.


4.8.2 Chargeable calls to 3 digit codes. (100, 102, 103 etc)

When such a code is keyed the box will condition itself to refund any coins inserted for a period of 40 seconds after the final digit has been keyed.

This is to prevent money being inserted and stared before it can be monitored by an operator. Coinbox identity tone is generated and will remain on for the duration of the call.


4.8.3 When coins are inserted, coin value tones are transmitted to line but are inaudible to the user. The tones are:


2p One short pip of 400 hz tone

10p three short pips of 400 hz tone

50p One long pip of 400 hz tone


The capability exists of transmitting an additional signal of two short pips,

4.8.4 3 digit non chargeable codes. ( 999, 151 etc.)


These are similar to those to chargeable codes but the identity tone is not generated and the box will refund inserted coins throughout the call.


4.8.5 Chargeable operator controlled calls made as 'follow on' calls after a keyed call has been made, with credit remaining,


In this circumstance the residual credit is 'frozen'. Coins inserted on the instruction of the operator will be cashed immediately (with coin value tone transmission,) but the credit stored in the memory will remain unaltered. On completion of the timed, prepaid operator call the remaining credit may be used for further auto calls as if there had been no interruption, or, if the handset is replaced, the box will cash up taking account only of the auto call charges,


4.9 Coin validation.


4.9.1 Maximum diameter and maximum thickness are gauged by the coin entry plate


4.9.2 Minimum diameter, minimum thickness and the material content of coins are checked by the coin checker. For the thickness and diameter check see E5C 3103 for details.           


4.9.3 The material check is carried out electronically whilst the coin is momentarily held stationary in the coin runway.


4.9.4 The passage of the coin from the point of entry to the coin checker to the position in which the material check is carried out is timed precisely. If this is not completed within a set time, eg because the coin is on a string, the coin will be rejected and the string (if any) will be cut, If the time is exceeded due to the presence of foreign material in the runway, the release of the coin check flap is likely to cause the coin to be rejected and the foreign material to drop clear.


4.10 Self diagnostics.

When the handset's on hook the box is programmed to perform a self routining sequence. On the boxes to be used for the field trial this will be limited to monitoring the cash container full probe and detection of an obstruction in any of the coincheckers. Detection of a coin checker obstruction causes the release of an alarm relay. Since this relay will also release in the event of a power failure this condition also will be detected.


4.11Self reporting,

In the event of a cash container full condition being detected the alarm relay will flash and cause alternate loops and disconnection's to be applied to a second pair back to a central point. In the event of a coin checker obstruction the alarm relay will release permanently and connect a permanent loop to the fault reporting pair. The same condition will apply in the event of power failure.


4.12 For the purposes of the field trial the fault reporting cable pairs will be terminated on a specially provided equipment located at a suitable central point. An alarm condition will cause a lamp to light - flashing for a cash container alarm, steady for a fault requiring engineering attention. An optional audible alarm will be provided together with a 'receiving attention' facility. Removal of the alarm condition from the fault reporting pair will give a positive indication at the central station.

(Note: It is planned that the self routining capability will be considerably enhanced if the CT 22A is purchased in quantity so that faults can be detected in many of the main sub assemblies and a coded signal produced which will indicate which assembly is faulty. The self reporting capability will also be enhance( to transmit the coded fault signal, hopefully over the normal coinbox line.)



They formed an alliance with AGI (Aeronautical and General Industries (of
Croydon and Verwood) which was known as AGITELCO and the CT22s were purchase
from that body corporate.

It looks to me like the same case was used on a train 

Extract from nordic booklet 1983