Scanway
The Scanway Unit comprises of two parts; the Coin validator unit and the main coin handling mechanism (not sure of its official name!). The two parts are held together by 3 screws. When a coin is inserted into the Payphone, if the handset is still on-hook, then the coin simply drops down to the Coin return bin at the bottom by following the blue lines in the diagram below.
If the handset is off-hook, the coin is passed through the Validator unit in order to determine the value of the coin deposited. The Validator unit houses the electronics (located behind the blue cover at the top of the unit) and the actual scanning unit below (underneath the black cover). The scanning unit comprises 3 components;
1) An IR emitter/receiver pair to detect for the presence of any blockages within the coin validator unit.
2) A "SunWize Technologies" optical scanning sensor, presumably to detect the size of each coin.
3) A coil sensor, presumably to detect the metallic 'signature' of each coin?
If the coin is positively identified, it passes through to Coin position 1, where it is held in place by a solenoid-controlled bar. The CT54 can store up to 4 coins in total with additional coins following the same path and being stored in positions 2, 3 & 4 respectively. If a subscriber deposits a 5th coin into the Payphone whilst all 4 coin positions are occupied, the coin will be blocked by the gate just before position 4 and the coin will follow the Coin Bypass route marked in Green in the diagram below. Once a call is in progress and individual coin credit is used up, the coin in position 1 will be released into the cashbox and any other coins in positions 2, 3 and 4 will advance downwards to take up positions 1, 2 and 3. This process is repeated until there are no more coins stored in the Scanway unit. Once coin positions are freed-up, this allows the subscriber to deposit more coins as necessary, again up to a maximum of 4 at any one time.
At the bottom of the coin run is a Yellow gate, again, controlled by a solenoid. At rest, this gate directs coins passing through it into the Cashbox. When the solenoid is energised, the gate flaps inwards towards the front of the Payphone and directs coins into the Coin return bin.
Once a call has been completed, any remaining coins stored in the Scanway unit drop through coin positions 4, 3, 2 and 1 and finally through the gate at the bottom. This is how the Payphone returns unused coins to the caller whilst cashing coins that are needed to pay for the call.
There are Infra-Red sensors contained within the main coin handling unit to detect for blockages and stuck coins - these can be seen flashing away with the aid of a Smartphone. A lot of the coin handling parts of the Scanway unit can be easily disassembled to clear blockages or foreign objects that may have been inserted.
Coins
It worth mentioning something about coins. Obviously, as new coins are introduced, the Scanway software will need updating to be able to recognise these. Inevitably, once the Payphone is taken out of service, then these updates are not possible and so you will probably find, as I did, it will only accept certain coin types.
So far as 10p's are concerned, my payphone will only really accept the original 10p pieces that were minted 1982-2008. The newer 'Segment of the Royal Shield' coins minted from 2008 are not registered by the scanway unit and tend to get simply deposited straight in the cashbox.
It's a similar story with the 20p's also. The 1982-2008 variants it is generally happy with, but from 2008 onwards, these coins tend to be rejected by the Scanway unit. I'm not entirely sure what the difference is be it the weight or dimensions, however I find I have to remove these from any change I have before using the payphone.
Since the minimum amount needs to be 60p to make a call, then invariably you'll need a supply of either 20p or 50p's pieces, since the Scanyway unit can only hold 4 coins simultaneously.
50p's dont tend to be a problem, regardless of vintage and it appears to accept pretty much any variant of these.
Finally, the £1 needs to be the old-fashioned round-type and not the newer 12-sided variant that was introduced in 2016. These are still readily available off auction sites or from some local laundrettes who still use them for their washing machines/tumble-dryers!