Circuit for firing paystation coin relay using power derived from telephone line tip/ring voltage

Increased power to operate a paystation coin relay is derived from the tip/ring pair by means of a power boost circuit, which is controllably coupled to the tip/ring pair when the coin relay is to be fired. To fire the coin relay, a line coupling relay circuit is energized, so as to apply the tip/ring line voltage to a D.C.-to-D.C. converter, the output of which is coupled to current storage (capacitor) circuit. The output of the current storage circuit is coupled to a first switch circuit and monitored by a comparator. The first switch circuit has an output coupled in circuit with the coin relay. In response to the comparator detecting that the current storage circuit has accumulated sufficient electrical energy to fire the coin relay, the comparator enables the first switch circuit, so that the output of the current storage circuit is applied to the coin relay, thereby firing the coin relay, to either collect accumulated coins or return the coins to the paystation user, depending upon a controllably established coin relay current flow path to the coin relay winding. The output of the comparator is further coupled through a delay circuit to a second transistor switch circuit which is coupled to the line coupling relay. The second switch circuit is operative to apply a de-energizing potential to the line relay a prescribed period of time subsequent to the firing of the coin relay, thereby returning the line relay to its normal state.

FIELD OF THE INVENTION 
The present invention relates in general to telephone systems and is 
particularly directed to a paystation telephone circuit for controlling 
the operation of a coin relay using power derived from the telephone line 
(tip/ring) voltage. 
BACKGROUND OF THE INVENTION 
Because of the magnitude of the electro-mechanical force employed for the 
collection and refund of coins that have accumulated in the coin 
collection bin or hopper of a paystation telephone, the power requirements 
of the coin relay used to operate the bin are substantially greater than 
those of the signalling and audio circuitry of the paystation set. As a 
consequence, it has been a customary practice to derive coin relay power 
from a separate power source. In the case of a regulated line, the power 
for the coin relay is supplied directly from the central office. In the 
case of a customer owned, coin operated telephone (COCOT), however, this 
auxiliary power source must be provided on site, either by way of 
connection to a 110 volt A.C. line or by the installation of a separate 
battery. Both of these latter options are undesirable, as they require a 
separate power interface for the paystation circuitry, raise maintenance 
overhead and increase operating costs. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, the need for a separate power 
source to operate paystation components such as the coin relay, the power 
requirements of which are in excess of what is providable by way of the 
line differential voltage, are obviated by a power boost circuit, which is 
controllably coupled to the tip/ring pair through which audio signal 
processing is conducted. The power boost circuit is normally decoupled 
from the tip/ring pair, until the need for a specified paystation 
function, such as the operation of the coin relay to either collect or 
return coins to the paystation user, is required. However, the power boost 
circuit could be continually coupled and then simply activated to fire the 
coin relay. 
Pursuant to the invention, when the coin relay is to be fired, a line 
coupling relay circuit, through which the telephone line tip/ring pair is 
normally coupled to the audio signal processing circuit of the paystation, 
is energized, so as to apply the (48 V) differential of the tip/ring pair 
to a fast response time D.C.-to-D.C. converter, the output of which is 
coupled to current storage (capacitor) circuit. The output of the current 
storage circuit is coupled to a first (transistor) switch circuit and 
monitored by a comparator. The first switch circuit has an output coupled 
in circuit with the coin relay. In response to the comparator detecting 
that the current storage circuit has accumulated sufficient electrical 
energy to fire the coin relay, the comparator enables the first switch 
circuit, so that the output of the current storage circuit is applied to 
the coin relay, thereby firing the coin relay, to either collect 
accumulated coins or return the coins to the paystation user, depending 
upon a controllably established coin relay current flow path to the coin 
relay winding. The output of the comparator is further coupled through a 
delay circuit to a second transistor switch circuit which is coupled to 
the line coupling relay. The second switch circuit is operative to apply a 
de-energizing potential to the line relay a prescribed period of time 
subsequent to the firing of the coin relay, thereby returning the line 
relay to its normal state. 
As a further feature of the present invention, in addition to providing 
coin relay power from the power boost circuit, so that no external power 
source (110 A.C. line or separate battery) is required, a parallel circuit 
path is coupled to receive coin relay power by way of the central office, 
so that the invention may be incorporated in both COCOT and regulated 
paystations. When the coin relay is to be fired by way of the central 
office, the power boost circuit simply remains disabled, with the line 
coupling relay circuit providing a circuit path for the telephone line 
tip/ring pair to the audio signal processing circuit of the paystation. 
This circuit can be used in an integrated COCOT and regulated paystation 
telephone system as described in co-pending U.S. patent application Ser. 
No. 07/740,841, filed on even date herewith and being commonly assigned to 
the assignee of the present invention.

DETAILED DESCRIPTION 
Referring now to the single Figure of the drawings, a telephone line 
tip/ring pair 11, with an optional ground line from a central office for a 
regulated system, to which a paystation telephone is connected is shown as 
being coupled through an overvoltage protection circuit 13 (e.g. a 
back-to-back Zener diode pair bridging tip and ring) to a full wave bridge 
circuit 15, a first node 17 of which is coupled to a reference potential 
(ground) and a second node 19 of which is coupled to a line 21. The 
potential of line 21 is normally at some prescribed differential (e.g. 48 
V) relative to ground node 17 and is customarily coupled to the 
paystation's micro-controller and associated audio signal processing 
circuitry. As the details of such circuitry are unnecessary for an 
understanding of the present invention, no description will be given here. 
Pursuant to the present invention, interposed in line 21 is a latching type 
line coupling relay circuit 23, having a pair of coil windings 25, 27 and 
switchable contacts 29 and 44. When the line coupling relay circuit 23 is 
in its normally de-energized state, switchable contact 29 is in the 
position shown in the Figure, bridging a first contact node 31, which is 
in circuit with node 19, with a second contact node 32, which is in 
circuit with line 21. A third contact node 33 of line coupling relay 
circuit 23 is coupled via a line 35 to relay coil 27 and to a power 
accumulator circuit 41. Contact 44 includes a first contact node 40 
connected to the ground line when the paystation is coupled with a 
regulated line. A second node 42 connects with a collect/return control 
relay 93 described below. Power accumulator circuit 41 is comprised of a 
conventional D.C.-to-D.C. converter, such as a MAXIM model 641, coupled in 
cascade with a storage capacitor circuit. A D.C.-to-D.C. converter having 
a fast response time is preferable. Relay winding 25 is coupled between 
ground and a control line 37 from the paystation's microcontroller. Relay 
winding 27 is further coupled to the collector of a switching transistor 
53, to be described below. 
The voltage across the storage capacitor circuit within power accumulator 
circuit 41 is coupled via line 46 to a coin relay power switch circuit 61 
and to a first input 71 of a voltage comparator 73. A second input 72 of 
comparator 73 is coupled to a prescribed reference potential (e.g. on the 
order of several volts). Coin relay power switch circuit 61 includes a 
first bipolar switching transistor 63 having its base electrode 63b 
coupled via line 76 to the output of comparator 73, its emitter electrode 
63e coupled to ground and its collector electrode 63c is coupled through a 
resistor 65 to the base electrode 67b of a bipolar switching transistor 
67. Although each of the switching transistors of the power boost circuit 
is depicted as a bipolar device, it should be observed that the invention 
is not limited to the use of such devices and other electronic switching 
elements, such as field effect devices, may be used in their place. 
The collector electrode 63c of transistor 63 is further coupled via a line 
81 to a switching contact 92 of a collect/return control relay 93. Relay 
93 has a pair of control windings 94, 95. One end of each of windings 94, 
95 is coupled in common to receive a coil energizing voltage. The other 
ends of windings 94, 95 are respectively coupled to receive `collect` and 
`return` signals from the micro-controller, to delineate which of terminal 
pairs 96 and 97 are bridged by first switching contact 91 and a second 
switching contact 92 of relay 93. The outputs of terminal pairs 96 and 97 
are coupled via lines 101 and 102 to opposite ends of the coin relay 
winding within coin relay 100. 
The emitter electrode 67e of transistor 67 is coupled to line 46, while its 
collector electrode 67c is coupled via line 82 to a second side of the 
winding of coin relay 100. Output line 76 from comparator 73 is further 
coupled via a delay circuit 87 to the base electrode 53b of a switching 
transistor 53. The emitter electrode 53e of transistor 53 is coupled to 
ground, while its collector electrode 53c is coupled via line 55 to 
winding 27 of line coupling relay 23. To provide for auxiliary power 
control of the coin relay, lines 82 and 84 connect to ground on the 
regulated line and lines 81 and 83 connect to a high voltage bypass line 
14 output from a conventional high voltage bypass circuit 12 coupled to 
the tip output from the protection circuit 13. In this case, respective 
blocking diodes 85, 86 are inserted in the current flow path to the coil 
winding to isolate the C.O. sourced coin relay control from switching 
transistors 63 and 67. 
OPERATION 
As explained above, with line coupling relay 23 normally deenergized, the 
power boost circuit in accordance with the present invention is decoupled 
from tip/ring pair 11, so that the voltage (48 V) at node 19 of bridge 15 
is coupled via line 21 to downstream audio signal processing circuitry. 
Assuming that the paystation is a COCOT unit, then, when the coin relay 
100 is to be energized or `fired` at the completion of the call, for the 
collection or refund of coins that have been inserted into the paystation, 
the paystation's micro-controller will first set relay 93 via coils 94 and 
95 for collect or refund and then issue a `fire` signal via line 37 to 
winding 25 of line coupling relay circuit 23. 
In response to this coin relay firing signal, switchable contact 29 of line 
coupling relay 23 breaks the connection between relay nodes 31 and 32, 
thereby interrupting line 21, and makes the connection between nodes 31 
and 33, so as to apply the (48 V) differential of the tip/ring pair to the 
D.C.-to-D.C. converter within power accumulator circuit 41. The increased 
voltage output of the converter is coupled to the power accumulator's 
capacitor storage circuit, the output of which is coupled over line 46 to 
the emitter electrode 67e of switching transistor 67 circuit and to input 
71 of comparator 73. 
As the charge accumulated on the storage capacitor circuit within power 
accumulator 41 increases, comparator 73 detects when the increasing 
voltage exceeds the threshold reference voltage applied to comparator 
input 72, indicating that the storage capacitor circuit has accumulated 
sufficient electrical energy to fire the coin relay. At this time the 
output of comparator 73 changes state (goes high), thereby turning on 
switching transistor 63. Alternatively, power from node 19 can be 
continually coupled to the audio signal processing circuitry and the 
D.C.-to-D.C. converter, hence eliminating the relay. In this arrangement, 
the micro-controller can vary the V.sub.ref signal input to comparator 73 
to fire the coin relay 100. 
When transistor 63 turns on, the reference voltage (ground) at its emitter 
63e is coupled to the base 67b of transistor 67 and, via line 81 and one 
of lines 101, 102 (depending upon whether coins are to be collected or 
returned), to one side of the winding of coin relay 100. Switching 
transistor 67 is turned on by the low signal now applied to its base, 
thereby causing the accumulated firing potential on line 46 to be coupled 
through its emitter-collector path to line 82 for application to the other 
side of the coin relay winding, firing the coin relay. Whether or not 
coins deposited by the customer are to be collected or refunded will 
depend upon the application of a `collect` signal or a `return` signal to 
the respective windings 94, 95 of relay 93, as described above. 
A prescribed period of time (e.g. 400 ms.) after the output of comparator 
73 changes state, delay circuit 87 applies the high on line 76 to the base 
electrode 53b of transistor 53, thereby causing a low voltage to be 
coupled through transistor 53 to winding 27 of line coupling relay 23, 
thus de-energizing the line relay and returning its switchable contact 29 
to its normal state, bridging line 21 to restore the line voltage to the 
audio signal processing circuitry and decoupling the power boost circuit 
from the tip/ring pair. 
The foregoing description of the operation of the coin relay power boost 
circuit in accordance with the present invention applies to the 
installation of the circuit in a COCOT or regulated line paystation 
telephone. Where the paystation is controlled by the central office via a 
regulated line, the microcontroller can optionally supervise the line 
coupling relay or, when not supervising, then the current necessary to 
fire the coin relay is coupled directly to collect/return control relay 93 
via auxiliary lines 83, 84, as described previously. 
As will be appreciated from the foregoing description, the conventional 
necessity of deriving coin relay power from a power source separate from 
that available from the line circuit in an unregulated paystation 
environment is obviated in accordance with the controllable power boost 
circuit of the present invention which, advantageously, is readily coupled 
with the tip/ring pair through which audio signal processing is conducted, 
so as to minimize maintenance and operating overhead. By means of an 
auxiliary parallel path the coin relay is also controllable by means of 
the central office, so that the present invention has utility in both 
regulated and unregulated paystation telephones. 
While we have shown and described an embodiment in accordance with the 
present invention, it is to be understood that the same is not limited 
thereto but is susceptible to numerous changes and modifications as known 
to a person skilled in the art, and we therefore do not wish to be limited 
to the details shown and described herein but intend to cover all such 
changes and modifications as are obvious to one of ordinary skill in the 
art.