Patent GB-1070005-A (GB)
Title: Apparatus for determining the difference between two values
Inventor: COLLINS ALAN DESTIN
IPC: G06J1/00
Filed: 1962-11-15
Abstract: 1,070,005. Change delivery apparatus; electric analogue calculating. ELECTRONIC MODULES Ltd. Nov. 15, 1963 [Nov. 15, 1962], No. 43214/62. Headings G4G and G4X] An arrangement for registering cost and credit and determining the difference between them for the purpose of giving change comprises three identical sets of resistors 41 to 44, 51 to 54, and 63 to 66, each resistor of a set being inversely proportional in value to the coin it individually represents and having one terminal connected permanently to a common voltage dividing point 45, the first set 41 to 44 being connected normally between a - 6 volt rail and 45 but being selectively connectible to an earth rail to register cost, the second set 51 to 54 being connected normally between the earth rail and 45 but being selectively connectible to the - 6 volt rail to register credit in response to received coins, the third set being normally connected between the - 6 volt rail and 45 but being connectible in sequence of diminishing monetary significance to the earth rail so as to augment the cost registration and establish what resistors of the third set are needed to obtain a potential at the voltage dividing point 45 indicating a balance between credit and cost. The resistors of the third set 63 to 66 needed to obtain the balance give a direct indication of the coins required as change; these resistors being connected to the - 6 volt rail over low value resistors and being switched to the earth rail by successive switching of transistors 62. The cost registration is set up by setting switches 46 manually. Credit is registered by coin actuation of switches 55. On registration of credit, clock pulses drive a stepping register from a standby position over four intermediate states to an end position. The first intermediate position sets a bi-stable circuit, the output of which switches transistor 62 to take resistor 63 from the - 6 volt rail to the earth rail and energizes a latch solenoid to prepare for the delivery as change of a coin corresponding in value to resistor 63. If resistor 63 changes the voltage at dividing point 45 beyond its normal balanced value, a transistor, the base of which is connected to a reference potential at 103 and is gated to the dividing point 45 by a pulse on lead C, becomes conductive to produce a pulse on lead E. The pulse on lead E is used to restore the bi-stable circuit, thereby disconnecting resistor 63 and cancelling the preparation for dispensing a coin as change. If the resistor 63 moves the voltage at point 45 towards or to its normal value, the bi-stable circuit stays set leaving resistor 63 connected. Whatever the result the register is moved to its next intermediate position operating a second bistable circuit to try the connection of resistor 64. Resistors 65 and 66 are similarly tried. The end position of the register produces an output to energize a change dispensing solenoid after which the circuits are reset pending a further transaction. The clock pulses and stepping register may control a separate cost/ credit register and change indicator; the first arrangement handling copper values of 3d., 1d. and ¢d., while the second arrangement handles silver values of 2s., 1s. and 6d.