POA payphones - Fraud prevention feature

POA payphones - Fraud prevention feature

Post by The Technical Manage » Tue, 26 Mar 2002 22:18:28



When a coin is inserted into a POA payphone it imposes a train of high
resistance pulses on the line corresponding to each coin unit value.
This pulse train then follows with a short open circuit period.
According to the specification of the POA payphone and the coin and  fee
checking relay sets it claims that this open circuit period is a fraud
prevention feature. How on earth is this actually supposed to work and
if there was no open circuit period then how could a POA payphone be
defrauded ?

My strowger coin and fee checking relay set from 1962 does check for the
open circuit period after the coin pulse train and if it isn't there it
implements a forced release on the line. OTOH my TXE4 electronic coin
and fee checker circuit from 1979 doesn't check for the open circuit
period.

 
 
 

POA payphones - Fraud prevention feature

Post by Steve Arnol » Wed, 27 Mar 2002 00:21:25


Hi,

if I remember correctly from way back, when you insert a coin in the coinbox
slot, it raised a cam which would then fall after the coin had passed.This
is what made it quite hard to push the coin into the box.  The falling cam
is what generated the pulses according to coin value. The coin would then
pass down a chute where it was checked for weight diameter thickness to
ensure it was a valid coin. If not it would drop out of the chute. Only if
it made it to the end of the chute (i.e. a valid coin) would it operate a
switch called the mask. This switch is what produced the open circuit. I
hope that is clear, I know what I mean anyway :-)

Steve.



Quote:> When a coin is inserted into a POA payphone it imposes a train of high
> resistance pulses on the line corresponding to each coin unit value.
> This pulse train then follows with a short open circuit period.
> According to the specification of the POA payphone and the coin and  fee
> checking relay sets it claims that this open circuit period is a fraud
> prevention feature. How on earth is this actually supposed to work and
> if there was no open circuit period then how could a POA payphone be
> defrauded ?

> My strowger coin and fee checking relay set from 1962 does check for the
> open circuit period after the coin pulse train and if it isn't there it
> implements a forced release on the line. OTOH my TXE4 electronic coin
> and fee checker circuit from 1979 doesn't check for the open circuit
> period.


 
 
 

POA payphones - Fraud prevention feature

Post by The Technical Manage » Wed, 27 Mar 2002 23:32:19



> Hi,

> if I remember correctly from way back, when you insert a coin in the coinbox
> slot, it raised a cam which would then fall after the coin had passed.This
> is what made it quite hard to push the coin into the box.  The falling cam
> is what generated the pulses according to coin value. The coin would then
> pass down a chute where it was checked for weight diameter thickness to
> ensure it was a valid coin. If not it would drop out of the chute. Only if
> it made it to the end of the chute (i.e. a valid coin) would it operate a
> switch called the mask. This switch is what produced the open circuit. I
> hope that is clear, I know what I mean anyway :-)

When the mask contact is activated by a valid coin reaching the end of the
chute it allows the coin pulses to be sent to the line. Contact CPON3 is what
produces the 60 ms open circuit period.

> Steve.



> > When a coin is inserted into a POA payphone it imposes a train of high
> > resistance pulses on the line corresponding to each coin unit value.
> > This pulse train then follows with a short open circuit period.
> > According to the specification of the POA payphone and the coin and  fee
> > checking relay sets it claims that this open circuit period is a fraud
> > prevention feature. How on earth is this actually supposed to work and
> > if there was no open circuit period then how could a POA payphone be
> > defrauded ?

> > My strowger coin and fee checking relay set from 1962 does check for the
> > open circuit period after the coin pulse train and if it isn't there it
> > implements a forced release on the line. OTOH my TXE4 electronic coin
> > and fee checker circuit from 1979 doesn't check for the open circuit
> > period.

 
 
 

POA payphones - Fraud prevention feature

Post by Adrian Kennar » Mon, 01 Apr 2002 03:50:09




>>Hi,

>>if I remember correctly from way back, when you insert a coin in the coinbox
>>slot, it raised a cam which would then fall after the coin had passed.This
>>is what made it quite hard to push the coin into the box.  The falling cam
>>is what generated the pulses according to coin value. The coin would then
>>pass down a chute where it was checked for weight diameter thickness to
>>ensure it was a valid coin. If not it would drop out of the chute. Only if
>>it made it to the end of the chute (i.e. a valid coin) would it operate a
>>switch called the mask. This switch is what produced the open circuit. I
>>hope that is clear, I know what I mean anyway :-)

> When the mask contact is activated by a valid coin reaching the end of the
> chute it allows the coin pulses to be sent to the line. Contact CPON3 is what
> produces the 60 ms open circuit period.

I presume it also helped make it difficult for someone putting
a normal phone in parallel on the line.

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POA payphones - Fraud prevention feature

Post by John He » Mon, 01 Apr 2002 06:06:34






>>>Hi,

>>>if I remember correctly from way back, when you insert a coin in the coinbox
>>>slot, it raised a cam which would then fall after the coin had passed.This
>>>is what made it quite hard to push the coin into the box.  The falling cam
>>>is what generated the pulses according to coin value. The coin would then
>>>pass down a chute where it was checked for weight diameter thickness to
>>>ensure it was a valid coin. If not it would drop out of the chute. Only if
>>>it made it to the end of the chute (i.e. a valid coin) would it operate a
>>>switch called the mask. This switch is what produced the open circuit. I
>>>hope that is clear, I know what I mean anyway :-)

>> When the mask contact is activated by a valid coin reaching the end of the
>> chute it allows the coin pulses to be sent to the line. Contact CPON3 is what
>> produces the 60 ms open circuit period.

>I presume it also helped make it difficult for someone putting
>a normal phone in parallel on the line.

Not really.

5k resistor and a diode in series placed across the dial impulsing
contacts.

Dial normally (diode not conducting).

Current reversed from exchange on answer (to unlock coin slots).

Dial (sending coin pulses as diode now conducting).

If C&FC requires break pulse, flash receiver rest.

Quote:

>--
>   _                Andrews & Arnold Ltd, 0871 871 4444 http://aa.nu/
>  (_) _| _ . _  _   ADSL without the 12 month tie in. http://adsl.ms/
>  ( )(_|(  |(_|| )  ADSL with fixed IP in 3-5 days... http://adsl.ms/
>  ~~~~~~~~~~~~~~~~  Need a good firewall:  http://www.FireBrick.info/

--

[ John Hein              GM1YME  |       Phaggots do it on the phone!       ]


[ Telephone: +44 131 558 1279    |http://www.scotsgay.co.uk/people/john.html]
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