GB2043968A

GB2043968A - Improvements in and relating to switches and to timing apparatus controllable by such switches

Info

Publication number: GB2043968A
Application number: GB8003759A
Authority: GB
Original assignee: TURNRIGHT CONTROLS
Current assignee: TURNRIGHT CONTROLS
Priority date: 1979-02-05
Filing date: 1980-02-05
Publication date: 1980-10-08
Also published as: DE3003847C2; IT8047814A0; DE3003847A1; FR2448177A1; GB2043968B; IT1207089B

Abstract

A timing circuit arrangement suitable for timing cooking operations in which "time of day", "cook time" and "ready time", for example, are required, includes a time-division- multiplexed electrical system comprising IC11 Fig. 3 which provides data input, data output and address output highways. Switches are connected between the highways for controlling the system, and a digital time display (not shown) is connected between the data output and address output highways 12, 13 for displaying selected contents of an alterable data store or register within IC11. The set time switches S1, S2 Figs. 1, 2, 5 may be operated by means of a rotatable member. Pulse sequences, Fig. 1A, from S1, S2 are fed via D2, D4 to inputs K2, K4 of IC11. The latter samples the states of K2, K4 periodically and establishes conditions within the alterable store according to the logic states of K2, K4 during two consecutive samplings and whether the states have changed. Clockwise rotation of the member results in accompanying changes in the contents of the alterable data store, the changes being shown as sequential incrementing of the display, and anti-clockwise rotation result in decrementing. Rotation results initially in changes to the units of the display, but when a 9 to 0 change occurs, changes to the tens follow thereafter until adjustment ceases. A rotary control switch suitable for controlling the timing circuit employs components e.g. Reed contacts Figs. 1, 2 or Hall effect devices sensitive to a magnetic field to act as the input switches, and changes of the magnetic field takes place as a rotatable member is moved. <IMAGE>

Description

SPECIFICATION Improvements in and relating to switches and to timing apparatus controllable by such switches This invention relates to switches and to timing apparatus controlled by switches. The switches may provide an output that indicates or can be adapted to indicate both the extent of movement of the switch and the direction of movement of the switch. In the case of a rotary switch, the output indicates the angular movement or angle turned through of the switch and whether the rotation is clockwise or anti-clockwise.

Special switches may find particular application in the control of timing circuits, for example clocks which may be of the digital kind, i.e., that in which a digital display is used. The switch is used to increment or decrement the circuit and hence the display.

It has been proposed to employ a switch in which each of two or more contacts is opened and closed mechanically by a moving, for example a rotary, component of the switch. However, the contacts are usually open to atmosphere and thus liable to corrosion whilst the mechanical operation calls for careful adjustment of the moving parts and maintenance during use.

In respect of switches, the present invention contemplates the replacement of the mechanical operation by a magnetic operation. Relative movement between a magnetic field and components sensitive to the field may be arranged to produce the necessary output to indicate both the extent of movement and the direction of movement.

The relative movement may be produced by a moving, for example rotating, permanent magnet in the magnetic field of which are positioned components sensitive thereto, for example reed relays or Hall effect devices. Alternatively, the devices may be movable into and out of a fixed magnetic field.

Alternatively, the components may be located in the magentic field but are normally screened from the effect thereof by a movable magnetic screen. The screen is apertured at one or more points in such manner as to permit the magnetic field to actuate the components. The aperture need not be a physical aperture but merely an area of the screen penetrable by the magnetic field.

A further desirable, although optional, feature is the addition to the moving member of the switch of sufficient mass to increase substantially the inertia of the member. Once such a member commences to move it will continue to move for some time. In the case of a rotary member, the inertia may be increased by the addition of a flywheel.

In respect of timing apparatus controlled by a switch, timing circuit responsive to the output of the switch may comprise a clock with, usually a digital display, the output of the switch being used to increment or decrement the clock at a particular rate or rates. Such incrementing or decrementing is of particular advantage when the clock is used to time operations, for example cooking operations, and has to be set to initiate an operation at a particular time and/or to control the period during which an operation is to be carried out.

According to the invention, a timing circuit includes (i) an electrical system providing a data input port, a data output port, and an address output port and which, in operation, provides pulses on the address output port, (ii) first and second switches connected between the data input port and the address output port to respective first and second parts of the data input port, and operable to set a time for the timing circuit by returning address pulses to the input data port, (iii) a control member or members arranged to operate the switches, (iv) a digital display connected to the data output and the address output portS, (v) a first group of storage cells, included in the electrical system, the states of which the digital display is arranged to display, (vi) storage means, included in the electrical system, the state of which determines, at least partly, if any alteration is to be made to the first group of cells, and if so, the nature and the extent of the alteration, (vii) logic elements, included in the electrical system, arranged to effect alteration of the states of the first group of cells at least partly in accordance with the state of the storage means, wherein operation of the or a control member is effective to provide orderly changes to the states of the first group of cells in accordance with the state of the storage means to give sequentially incremented and sequentially decremented displayed values, and, in operation, the least significant digit of the display changes initially, until it reaches a trigger value, after which the trigger value remains and changes are confined to the higher order digits, for constant operation of the control member.

Advantageously, the storage means has a rest state when the or each control member is undisturbed, and a fully set state which is achieved only when the least significant digit reaches its trigger value during operation of the or a control member, and the storage means returns to its rest state on cessation of control member operation. Preferably, the storage means returns to its rest state after a delay with respect to the cessation of control member operation. Preferably, the storage means has an intermediate state at which it remains when the control member is operating with the least significant digit at a value other than its trigger value.

Advantageously, the storage means consists of a second group of storage cells, the combined states of which represent the said state of the storage means. Preferably the second group of storage cells is arranged as an incrementing counter. Preferably, the incrementing counter is reset to its start value when the least significant digit reaches its trigger value.

In the case of some operations, not only has the clock to be set but in addition the user may have to activate or set another device or devices and if such activation or setting is not carried out, the desired operation will not be effected.

In the case of a cooking operation, the user has also to set the temperature at which the cooking operation is to be carried out, such setting preparing the oven heater for energisation at the start of the cooking operation.

The present invention also envisages the inclusion of a warning device which is able to provide a warning that may be visual or audible indicating to a user that not all of the actions necessary to the successful implementation of an operation have been carried out.

It will be understood that a timing circuit incorporating the warning device may be responsive to the output of a controlling switch other than that based on the magnetic operation described above. The switch may employ mechanically-operated contacts or photo-electric devices to produce the indication of extent of movement and direction of movement.

Alternatively, the input to the timing circuit to increment or decrement the latter may be provided by a multi-position switch with positions in which different rates of incrementing or decrementing are provided, or by several separate switches together providing the same facilities.

In the case of a timer for a cooker, there must be included a "function" switch that allows the clock to display both "ready time" and "cook time" and- allows both these times to be adjusted by the increment/decrement input. Such adjustment is subject to interlock to make incorrect settings impossible. If the "cook time" alone is altered, the cooker is programmed to operate in a semiautomatic mode and cooking commences immediately and is discontinued automatically on the expiry of the "cook time", that is to say the "ready time" varies according to "cook time" to register completion of the cooking operation. Adjustment of "ready time" is not permitted to vary "cook time".

Thus, at first, "ready time" may only be adjusted forwards, initiating a fully automatic cooking operation or mode. In such a mode, variation of "cook time" leaves "ready time" unchanged, unless "cook time" is increased to the limit of "ready time" minus time of day. If that happens, the cooking operation commences immediately as in the semi-automatic mode described above.

Preferably, in the event that "cook time" is increased to equal "ready time" minus time of day, the display "freezes" to indicate that fact to the user. If the user then carries on incrementing "cook time", "ready time" is also incremented automatically and a semi-automatic cooking mode ensues.

If, during a cooking operation, the function switch is turned to "cook time", the time displayed is that remaining to the end of the cooking operation, in other words, the "cook time" is automatically decremented as cooking proceeds.

The timing circuit may incorporate a warning light which glows steadily to indicate when the fully automatic mode has been selected. If the user fails to set the cooking temperature the light may "blink" and if the user fails to set the "cook tirne" the light may "flash". Such visual warnings indicate to the user that the controls have been incorrectly set.

Alternatively, the timing circuit may incorporate a warning device that produces an audible warning that may be interrupted at one frequency if the user fails to set the cooking temperature and at another different frequency if the user fails to set the "cook time".

The timing circuit may also incorporate a "minute timer" selectable at will by the user and which is settable to a time period up to a preselected maximum of 99 minutes and which, on the expiry of the set period gives an audible or visual warning. The set period may be shown on the clock display using the last two digit positions of the normal four-digit display or two additional digit positions may be used. A "cancel" control, for example a push button, is provided to enable the user to extinguish the warning and the display. Desirably, the setting of the time is accomplished by the switch that increments/decrements the clock, application of the output of that switch to the minute timer being determined by the function switch.

By way of example only, an embodiment of a control switch and of a digital timer circuit for an electric cooker will now be described in greater detail with reference to the accompanying drawings of which: Figs. 1 and 2 are, respectively, front and side view of the switch shown in diagrammatic form only, Fig. 1 A is an explanatory pulse diagram, Fig. 3 is a circuit diagram in block schematic form of the digital timer circuit, Figs. 4 and 5 show in detail the switch connections of the digital timer circuit, Figs. 6 to 9 are flow diagram representations of operations within the timer circuit, Fig. 10 is a circuit diagram representing the fixed component equivalent of part of Fig. 3 which responds to push button control members, and Fig. 11 is a circuit diagram representing a fixed component equivalent of part of Fig. 3 which responds to push button control members,and Fig. 12 is a schematic representation of an alternative form of rotary control switch suitable for use in Fig. 3.

Referring first to Figs. 1 and 2, a printed circuit board 1 supports a bearing 2 for a shaft 3 rotatable, in the bearing, about its longitudinal axis. Further support for the shaft is provided by a bracket 4 fixed to the printed circuit board. Mounted upon the shaft 3 for rotation therewith is a permanent magnet 5 shown as a bar magnet but which may take other physical forms.

Also mounted upon the board 1 within the magnetic field of the magnet 5 are reed relays 6 and 7.

The relays are so orientated that a space-mark ratio of about one is obtained for each set of contacts and a clearly defined phase difference between the outputs of the relays is achieved. This is illustrated in Fig. 1 A, the outputs of the two relays being indicated by the pulse train A, B. As can be seen, the spacemark ratio is about one and there is a phase difference of about 900 obtained. The direction of rotation of the shaft is, in the case of the pulse trains shown in Fig. 1A, anti-clockwise. As shown in Figs. 1 and 2, the relays are mounted in the plane of the board 1 itself at right angles to the axis of rotation of the shaft. The axis of each relay lies on line lying at 450 to a line drawn vertically through that axis.

To one end of the shaft 3 is secured a knob 8 by means of which a user can rotate the shaft. To the other end of the shaft is fixed a flywheel 9 consisting of several separate discs 10. The number of discs used determines the additional mass added to the shaft. The bracket 4 and knob 8 are not shown in Fig.

1.

As the knob is turned to rotate the shaft, the contacts of the relays 6, 7 make and break, the frequency thereof being determined by the speed of rotation and the order of making and breaking indicating the direction of rotation.

Thus, the switch generates two logic signals which change as the shaft is rotated.

The signals are arranged so that for a continuous rotation they change in quadrature. If their combined state is represented by AB, where A and B can take the values 0 or 1, the sequence of states for clockwise rotation may be written 00, 01, 11, 10, 00 while for anti-clockwise rotation it is 00, 10, 11, 01, 00 .... Of course, this order could be reversed.

These signals are sampled at intervals that are more frequent than the frequencies with which the signals might reasonably be expected to change. The sequence of sample pairs might thus take the form 00,00,00,00,01,01,01 the change after the fourth sample pair denoting a clockwise rotation of one unit. To allow the timing circuit to respond correctly to such a change, the two-bit sample AB is combined with the previous twobit sample CD to form a four bit composite number CDAB. (Clearly similar logical decisions to the following could be based on the reverse combination ABCD). The number 0101 indicates that the new pair are equal to the old pair, and that no change has occurred. The number 0001 indicates that a clockwise change has occurred, whilst 0011 denotes a double change of indeterminate sense, and is thus regarded as an error.The sixteen possible combinations can be listed as follows: Clockwise or positive change: 0001,0111,1110,1000 Negative change: 0010, 1011, 1101,0100 No change: 0000,0101,1111,1010 Double change, error: 0011,0110,1100,1001 If a code from one of the first two lists is recognised, the appropriate action of adding or subtracting one unit is taken, otherwise no action results.

In this embodiment the recognition algorithm takes the following form. It is apparent that if a group contains a code, it also contains its complement, for example, the first group contains 0111 and also 1000. If the most significant bit (the left most) is a 1, the complement of the code is taken, reducing the number of combinations to eight. These may be interpreted by their decimal equivalents, and the following table lists code, decimal equivalents, and corresponding movement represented as 0, - - or E which denotes a double move.

0000 0 0 0001 1 + 0010 2 0011 3 E 0100 4 - 0101 5 0 0110 6 E 0111 7 + Thus if the code has value 1 or 7 one unit is added, if the code has value 2 or 4 one unit is subtracted otherwise no action is taken.

The algorithm may be summarised thus: 1. Read in the signal pair.

2. Combine with the previous pair to form a four bit code.

3. Save the code for future use.

4. If the most significant bit of the code is 1, take the complement of all four bits.

5. If the code so formed represents decimal 1 or 7, initiate a positive action; if the code is 2 or 4 initiate a negative action, otherwise initiate no action.

6. Prepare the saved code for use with the next sample pair by shifting two places to the left, discarding the two most significant bits which represented the previous sample.

7. After any other necessary actions, return to 1 to repeat the cycle.

Instead of the reed relays, the switch shown in Figs. 1 and 2 could employ Hall effect devices, a suitable device being Type TI 1 72C manufactured by Texas Instruments Incorporated. Such a device provides a high impedance output that is switched to a low impedance in the presence of a magnetic field of suitable strength.

Fig. 3 shows, partly in block schematic form, the circuit diagram of a timing circuit suitable for an electric cooker and incorporating the facilities referred to above.

The circuit is based on an integrated circuit shown as block 11 which may be Type TMS 1070 manufactured by Texas Instruments Incorporated.

The integrated circuit Type TMS 1070 is organised as various stations, including an arithmetic logic unit, a fixed digital memory, an alterable digital memory, a data input port, a-data output port, an address output port, and respective data and control highways arranged to convey binary words, represented by electrical pulses, to and from the various stations of the integrated circuit. The various stations of the integrated circuit are in general arranged along the data and control highways, and are connectable to the highways on a time-division-multiplex basis for transferring electrical energy in pulse form between the various stations. The integrated circuit includes provision for a pulse generator which acts as a master clock for all time-division-multiplexing, and which also provides pulses for use as electrical energy packages within the circuit.The integrated circuit provides, on its address output port, time-division-multiplexing pulses for use by external circuit elements in synchronising operations with those within the integrated circuit, and on its data output port, data pulses representing binary words which are stored as electrical states in selected parts of the alterable digital memory.

The integrated circuit 11 provides outputs 12 and 1 3 to energise in a conventionai manner a digital display of four digits, and this display may be in 12 or 24 hour notation as required and may be qualified by the displaying of the letters a.m. or p.m. if desired. Alternatively, the display may incorporate four indicators for "morning", "afternoon", "evening" and "night". The output 1 2 is provided by the address output port designated RO-R7, and the output 1 3 is provided by the data output port designated 01-07, of the integrated circuit 11.

The minute timer output is shown, when selected, by the last two digits of the four-digit clock display although an extra two-digit display could be used if desired.

A control, for example the switch shown in Figs. 1 and 2, is connected to the integrated circuit 11 via diodes D1 and D2 and inputs K1, K2. The connections of the switch to the integrated circuit 11 are shown more explicitly in Fig. 5, the switch contacts being identified as S1 and S2. As indicated above, the condition of the contacts of the relays 6, 7 (i.e. open or closed) is sampled frequently by output R4 of the integrated circuit.

The output R4 of the integrated circuit 11 provides one of the time-division-multiplexing output pulses available for use by external circuit elements in synchronising operations with the integrated circuit. In this instance the external circuit element is the switch contacts S1, S2 which are arranged to return the pulses from the output R4 to the inputs K2, K4 of the integrated circuit. The pulse sequences presented to the inputs K2, K4 characterise the condition of the switch to the integrated circuit 11 which is provided with a specific cycle of operations for each possible switch condition. The integrated circuit selects and executes the cycle of operations appropriate to the pulse sequence it is receiving on its inputs K2, K4.The integrated circuit 11 tests the conditions of the inputs K2, K4 periodically at a frequency which is related to the mains supply frequency, and establishes conditions at specific locations within the alterable data store according to the states of K2, K4. The absence of pulses at both K2, K4 is recognised as the condition 00, the presence of a pulse on K2 alone is recognised as the condition 10, the presence of a pulse on K4 alone is recognised as 01, and the presence of pulses on both K2, K4 is recognised as 11. As explained above, the four-bit word associated with the presence or absence of pulses at K2, K4 during two consecutive sampling periods indicates to the integrated circuit the behaviour of a control member which is arranged to operate the switch contacts S1, S2.The integrated circuit determines the behaviour of the control member by the use of its arithmetic logic unit (ALU) to combine the data representing the previous and present states of the switches S1, S2. After using the present switch condition for a computation the integrated circuit saves the present condition for use as its previous condition in the next computation.

Where a rotary control member is used to operate the switches, the integrated circuit judges that the switch states have not changed since the last sample, the data thereafter selected from the fixed data store provides access to an address C in the alterable data store, and sets the value C = 1 5. C represents a group of cells in the alterable data store. As part of the same operation, the value of a further group of cells TT is incremented by 1 unless it is 15. The result of C = 15 is that a first group of cells in the alterable data store remain unaltered. In other words no time adjustment is made. The states of the cells of the said first group represent a value available for display. The value 7T = 1 5 represents a terminal value, and all values between TT = 0 and TT = 1 5 are available.

Where a rotary control member is used to operate the switches, when the integrated circuit judges that the switch states have changed since the last sample due to clockwise rotation, the value C = 0 is set and the value of TT is tested. If TT = 15 then no further change is made to C. If TT + 15, then the value of C is incremented by 1 to make C = 1, and TT = O is set. When C = 0 the states of the first group of cells are altered to correspond to a unit increment to a decimal display, and when C = 1, the states of the first group of cells are altered to correspond with an increment of ten to a decimal display. The frequency with which the display is incremented depends on both control member rotation and on the frequency at which the integrated circuit checks on the states of the switches S1, S2.This takes place several times in each second, and therefore the integrated circuit will detect no change in the conditions of the switches many more times than it detects a change even though the control member is rotating.

On each occasion that the integrated circuit detects no change in the switches it sets C = 1 5 and increments TT by 1. When the control member is rotated initially, the value of TT will already be 1 5. and therefore C = O will be set on the first change of switch states but TT = 1 5 will remain. As rotation continues C = O will be set periodically, and C = 1 5 will be set for the remainder of the time.TT = 1 5 will remain unaltered until a 9 to 0 change occurs in the units of the display, when Tut =0 will be set, making it possible for C = 1 to be set on the next switch change occurrence provided that switch rotation rate is high enough to catch TT at a value below 1 5. If rotation is maintained at that rate then C = 1 will be set periodically, C = 1 5 will be set for the remainder of the time, and TT will be kept to values below 1 5 through being reset to zero when C = 1 and incremented only while C = 1 5. If the rotation rate is low enough TT will be incremented often enough to go from 0 to 1 5 before the next switch change occurrence and C = 0 will be set periodically with TT = 1 5.In the detection of a 9 to 0 change in the units part of a decimal display, a variable T2 = O is set when the change occurs, and this is used to permit TT = O to be set.

Where a rotary control member is used to operate the switch contacts, the value C = 8 is set for anticlockwise rotation resulting in a change of the switch contacts, and the value of TT is tested. As before, if TT = 1 5 no further change is made to C, and if TT + 1 5 the value of C is incremented by 1 to C = 9 and the value TT = 0 is set. When C = 8 the states of the first group of cells are altered to correspond with a decrement of ten to a decimal display. The action and range of TT for anticlockwise rotation is the same as the action and range of TT for clockwise rotation.

It will be understood that instead of progressive incrementing of TT as described above, to set a start value of zero and a terminal value 1 5, the start value could be 1 5 and the terminal value could be zero and decrementing of TT could be used.

Part of the action of the integrated circuit in respect of the actuation of a pair of switches by means of a rotary control member may be realised in dedicated component form by means of a circuit as shown in Fig. 10, which shows a retriggerable monostable multivibrator 10, an OR gate 102, and three AND gates 103-105. All of the AND gates are two-input gates, the gate 103 providing an input port 106 to which a "change" pulse indicating a change in the switch conditions, is applied. The other input port 107 of the AND gate 103 is connected to the Q output port of the monostable multivibrator 101.The input ports 108, 109 of the AND gate 104 are connected to the input ports 106, 107 respectively, of the AND gate 1 03. The input port 110 of the OR gate 102 is connected to the output port of the AND gate 103, and the other input port 111 of the OR gate 102 is available to receive a pulse indicating a 9 to 0 change in a display units digit. The output port 112 of the OR gate 102 is connected to the trigger input port of the monostable multivibrator 1 01. The AND gate 1 05 has its input port 113 connected to the port 106 and its input port 1 14 connected to the Q output port of the monostable multivibrator 101. The output ports 1 5, 11 6 of the AND gates 104, 105 provide the output ports of the circuit. In operation, pulses indicating switch change are blocked by the AND gate 103 but are passed by the AND gate 105 because Q is at '1' to give a "change by 1" instruction at the output port 11 6, until a 9 to 0 change occurs and passes by way of the OR gate 102 to trigger the monostable multivibrator 101. The triggered monostable multivibrator 101 opens the AND gates 103 and 104, permitting further "change" pulses to give rise to an output pulse from the AND gate 104 for a "change by 10" instruction.

Returning now to the action of the integrated circuit 11, where a push button control is used to operate the switch contacts, when neither push button is operated, the integrated circuit will recognise that no switch has been closed by the absence of R4 pulses to K2 and K4 input ports, and set C = 15.

As part of the same operation, a variable T2 = 1 will be set. When the "increment" push button is operated, the integrated circuit will recognise that the switch is closed by the supply of R4 pulses to its K2 input port, say, and set C = O. Then T2 will be tested and it will be found that T2 = 1, so that C = 0 will remain, and the display will be incremented in units, the value of T2 being tested before each increment is made. The incrementing of the display in units will continue until the 9 to 0 change occurs, when T2 = O will be set, so that when T2 is next tested C will be incremented to C = 1, and incrementing of the display will continue in tens.Decrementing of the display is obtained when the "decrement" push button is operated to provide the K4 input of the integrated circuit with R4 pulses to set C = 8 for decrementing in units and C = 9 for decrementing in tens by the use of T2 as before.

Part of the action of the integrated circuit in respect of push button control of a pair of switches may be realised in dedicated component form by means of a circuit as shown in Fig. 11. The circuit is based on the operation of an R" bistable flip-flop 201 with its RESET input port connected to a control switch 202 by way of a buffer stage 203. The control switch is also connected to one input port 204 of a two-input AND-gate 206 which has its other input port 205 connected to the Q output port of the RS flip-flop 201. A second two-input AND gate 207 has one input port 208 connected to the port 204 and its other input port 209 connected to the Output port of the RS flip-flop 201. The SET input port of the RS flip-flop 201 is available to receive a pulse indicating a 9 to 0 change in a display.The output ports of the AND gates 206, 207 provide output indications for "increment by 10" and "increment by 1", respectively. In operation, on closure of the switch 202 the AND gate 207 provides a "1" output until the SET input of the RS flip-flop 201 goes high, when a "1" output becomes available from the AND gate 206.

Reference may be made to Fig. 6 which shows the flow sequence which deals with monitoring T2 and which is identified as GETT2. The routine GETT2 is also effective to set TT = 1 when T2 has just become zero. Fig. 7 may be referred to for a diagrammatic representation of the flow sequence for dealing with either a rotary or push button control member, the flow sequence being identified as GROTC for a rotary control switch and as GETC for a push button control switch. Fig. 8 provides an indication of the sequential arrangement of GROTC and GET2, and Fig. 9 provides an overview of the relationships between all the functions performed by the integrated circuit.

Details of the internal construction of the TMS 1070 integrated circuit are available in the booklet entitled "TMS 1000 Series Data Manual" published in 1976 by Texas Instruments Limited.

A time setting control arrangement for push button operation is shown in Fig. 4. In the arrangement of Fig. 4 switch contacts S1 and S2 are present as before and the circuit which includes S1 and S2 is connected to the R4 scanning pulse output port of the integrated circuit 11 as before. The switches S1 and S2 are arranged to be controlled by means of push button members. The possible switch combinations are both open, S1 open and S2 closed, and S1 closed and 52 open.When both S1 and S2 are open, then no scanning pulses reach the input ports K2 and K4 during the time during which there is a pulse on the R4 output line from the integrated circuit 11, and the integrated circuit 11 responds by taking no action in respect of time setting. The value C becomes 1 5 as previously.

When incrementing of the display is required, then S1 is closed, say, and this results in scanning pulses reaching the K2 input port of the integrated circuit 11 during the period R4. No pulses reach the K4 input port of the integrated circuit 11. The presence of scanning pulses on the K2 input of the integrated circuit 11 during the period R4 causes the execution of the previously described steps which result in the units part of the display being incremented. Incrementing of the units part of the display continues until the 9 to 0 change takes place, after which the tens part of the display alone continues to be incremented. The actions within the integrated circuit 11 are as previously described.

When decrementing of the display is required, then S2 alone is closed to supply scanning pulses to K4. The subsequent results inside and outside the integrated circuit 11 are also as described previously in respect of decrementing the display.

The method of time adjustment will be catered for by connection of suitable option diodes. In the case of the use of a rotary control member for example that shown in Figs. 1 and 2, response is provided to both angular movement and direction of rotation. Rotation of the control knob 8 results in changes of the display in 1 minute steps once the units part of the display has become zerQ, otherwise changes are effected in 1-minute steps.

Where the control is by means of separate switch members, changes may be initially in 1-minute steps until a ten or multiple thereof is reached when changes occur in 10-minute steps e.g. 25, 26,, 27, 28,29,30,40,50......

A non-zero setting of the units digit in the system with the rotary control member is effected by setting the multiple of ten just above or below the desired value and then pausing, after which rotation will effect changes in the units alone.

The function control is similarly connected and the state of the control is sampled by output R2 of the integrated circuit. The various settings of the function control and the displayed information are coded in the following manner: FUNCTION POSITION DISPLAY ADJUST K4 K2 K1 DEC.

1 COOK COOK O 0 0 0 TIME TIME 2 READY READY 1 0 0 4 TIME TIME 3 TIME 1 1 0 6 4 MINUTE MINUTE O 1 0 2 MINDER MINDER 5 MINUTE MINUTE O 1 1 3 MINDER MINDER 6 TIME 1 1 1 7 7 TIME TIME 1 0 1 5 Positions T-4 of the function switch control the cooker in the automatic mode whilst positions 5-7 control the cooker in the manual or non-automatic mode. The coding shown above is suitable for a four-digit display. If a six-digit display is adopted, only positions 1, 2, 3, 6, and 7 are required.

Via the output R10 of the integrated circuit a buzzer 14 is energised to indicate the end of a time period set up on the minute minder and this is inhibited and the minute minder display cancelled by operation of push button 1 5.

Energisation and de-energisation of the heating elements of the cooker oven is controlled by relay A/1 whose contacts Al are in series connection with those elements and the power input.

In the automatic position of the function switch, an indicator light 16 - which in the present case is a light emitting diode - is energised via outputs R7 and 01 of the integrated circuit and transistors T1 and T2. In the event of the user failing to set the oven temperature by means of an oven thermostat (not shown) the light 1 6 will be caused to "blink" by switching T1 on and off at a slow rate. That controls the conductivity of the emitter-collector circuit of T2 and the discharge of capacitor C1.

Similarly, if the user fails to set the "cook time", the light will flash by switching T1 at a higher rate, Correct setting of the necessary controls is indicated by a steady glow.

Option diodes D5, D6, D7 and D8 allow the inputting to the integrated circuit of extra facilities; a test circuit to enable the clock to be run at high speed; alternative power input frequencies e.g. 50Hz or 60Hz. 4 or 6-digit display, 1-2- or 24-hour display, type of control switch used, i.e. whether a rotary switch, a multi-position switch, or separate switches.

Other switching arrangements e.g. double pressure switches can also be catered for.

The various functions available for selection by the function control switch have specific locations within the alterable data store in the integrated circuit allocated to them. The integrated circuit displays the contents of a selected location within the alterable data store at its time-division-multiplexing frequency in order to provide a bright flicker-free display, and is interrupted briefly by the rising edges of the mains supply waveform to deal with the other functions it performs.

Provided that "time of day" has been set, the appropriate location in the alterable data store will contain a non-zero value, and there will also be values stored corresponding to "cook time" and "ready time", provided that these also have been set. The above times are set by the states of selected groups of cells within the alterable data store, as described, by the operation of a pair of switches. The integrated circuit uses the mains supply as a clock.oscillator for updating "time of day" and also for performing periodic updating of all other locations within the alterable data store.

As illustrated generally by Fig. 9 the integrated circuit serves the display most of the time until the appearance of the rising edge of a pulse derived from the mains supply signal. The display is selected by loading a register which dictates the states of the data output highway, with data selected for display.

The 50Hz mains supply pulses are counted, and are used to steer operations along one loop of Fig.

9 which results in "time of day" being incremented at appropriate periods, "cook time" and "minute minder" time being decremented at appropriate times, and a return to the servicing of the display.

At 50Hz mains supply pulses which are not second interval pulses, the other "non-time" functions are serviced. These "non-time" functions are split into three groups, one main group being serviced on most mains-derived pulses while each of the others is serviced in turn at about one-sixth second intervals. In each case, one function is dealt with and the integrated circuit returns immediately to dealing with the display.

As stated above, the integrated circuit is arranged to react if "cook time" is increased to equal "ready time" minus "time of day" by freezing the display of cook time.

The integrated circuit includes provision for keeping a record of "wait time", which is the period between "time of day" and "switch-on time". "Switch-on time" is "ready time" minus "cook time".

Once "ready time" is set, "wait time" is monitored as "cook time" instructions are received and no change in "cook time" is made if "wait time" would become negative by the execution of the instruction to change "cook time". That is, any instruction for a change in "cook time" which would lead to a negative "wait time" value if carried out is ignored. In the same way, if "cook time" has been set and attention is being made to "ready time", an instruction that would lead to a negative "wait time" if executed would be ignored. In addition, the integrated circuit ignores instructions which would lead to a "ready time" which exceeds 24 hours, that is, which would fall on the next day.This is achieved by testing for each instruction what "ready time" would become if the instruction were executed, before executing the instruction, and ignoring it if it puts "ready time" beyond the 24 hour mark.

In the monitoring of "wait time" by the integrated circuit, selected locations within the laterable data store are used to store values for "wait time", and on each instruction which affects "wait time", the stored value is copied into the arithmetic logic unit, changed by the amount indicated by the instruction, and the sign of the result is tested. If the result of the test leaves a negative value in the arithmetic logic unit, then the instruction is not carried out.

When "wait time" becomes zero when "cook time" is being incremented, "cook time" freezes because the integrated circuit is ignoring the input instructions. If the instruction persists when "wait time" has reached zero, then "ready time" is changed along with "cook time". Because of the above characteristics data held in the alterable data store and representing "cook time" and "ready time" is always valid. The variables "time of day", "wait time", "cook time", "switch-on time", and "ready time", will each be represented by the states of respective groups of cells within the alterable data.

When a non-zero "cook time" has been set, a lamp referred to above is energised periodically, and blinks to confirm the setting of "cook time". The alterable data store includes locations in which "cooking temperature" values are set, and the existence of "cooking temperature" values causes the lamp to be energised during the time it is not energised by the "cook time" non-zero value. Therefore with a "cooking temperature" value set, and no "cook time" value set, the lamp will flash. When both "cook time" and "cooking temperature" are both set the lamp glows steadily, the glow consisting of a combination of a "blink" and a "flash", corresponding to "cook time set" and "cooking temperature set", respectively.As shown in Fig. 1, a transistor T1 is so connected to the integrated circuit 11 that its base electrode is energised by the scanning pulse R7 from the integrated circuit 11, and its collector electrode is energised by an element of the output 13. The transistor T1 is effective to switch the auto lamp light emitting diode 1 6 on and off.

The alternative form of switch shown in Fig. 12 is a rotary switch having a shaft 301 on which is mounted a flywheel 302 having four poles 303 equi-spaced round its periphery.

Mounted in suitable manner adjacent the flywheel at positions 1350 apart are pick-up coils 304, 305 each wound on permanent magnet cores 306, 307 respectively. Conveniently, the pick-up coils and their associated magnets may be mounted upon a printed circuit board forming part of the structure of the switch.

As the shaft 301 is rotated, the passage of the poles 3 passed the pick-up coils produces changes in the flux path of the magnets and these changes induce voltages in the coils which are fed to amplifiers, for example high gain operational amplifiers (not shown). The amplifiers are such that each produces an output in the form of a train of pulses of substantially square waveform.

The pulse repetition frequency represents the rate of rotation of the shaft whilst the phase of one pulse train relative to the other indicates the direction of revolution of the shaft.

A typical timing circuit which is suitable for use with the switch just described is shown in Fig. 3, the outputs of the amplifiers being applied via diodes D1 and D2 to inputs K1 and K2 of the integrated circuit. The operation then follows the description given in that Specification.

It will be appreciated that the flywheel 302 could have only two poles 303-these being diametrically opposed-and two pick-up coils at positions spaced by 900. Other arrangements are possible which provide both an indication of the rate of rotation of the shaft and the necessary phase difference to indicate direction of rotation.

Claims

1. A timing circuit including (i) an electrical system providing a data input port, a data output port, and an address output port and which, in operation, provides pulses on the address output port, (ii) first and second switches connected between the data input port and the address output port to respective first and second parts of the data input port, and operable to set a time for the timing circuit by returning address pulses to the input data port, (iii) a control member or members arranged to operate the switches, (iv) a digital display connected to the data output and the address output ports, (v) a first group of storage cells, included in the electrical system, the states of which the digital display is arranged to display, (vi) storage means, included in the electrical system, the state of which determines, at least partly, if any alteration is to be made to the first group of cells, and if so, the nature and the extent of the alteration, (vii) logic elements, included in the electrical system, arranged to effect alteration of the states of the first group of cells at least partly in accordance with the state of the storage means, wherein operation of the or a control member is effective to provide orderly changes to the states of the first group of cells in accordance with the state of the storage means to give sequentially incremented and sequentially decremented displayed values, and, in operation, the least significant digit of the display changes initially, until it reaches a trigger value, after which the trigger value remains and changes are confined to the higher order digits, for constant operation of the control member.

2. A timing circuit as claimed in claim 1, wherein the storage means has a rest state when the or each control member is undisturbed, and a fully set state which is achieved only when the least significant digit reaches its trigger value during operation of the or a control member, and wherein the storage means returns to its rest state on cessation of control member operation.

3. A timing circuit as claimed in claim 2, wherein the storage means returns to its rest state after a delay with respect to the cessation of control member operation.

4. A timing circuit as claimed in claim 3, wherein the storage means has an intermediate state at which it remains when the or a control member is operating with the least significant digit at a value other than its trigger value.

5. A timing circuit as claimed in claim 4, wherein the storage means consists of a second group of storage cells the combined states of which represent the said state of the storage means.

6. A timing circuit as claimed in claim 5, and including a time-dependent variable member having a start condition representing a start value, a terminal condition representing a terminal value, and timedependent intermediate conditions representing intermediate values, wherein the time-dependent variable member is arranged, when at it terminal value, to limit the storage means to its intermediate state.

7. A timing circuit as claimed in claim 6, wherein the time-dependent variable member is an incrementing counter.

8. A timing circuit as claimed in claim 7, wherein the incrementing counter is reset to its start value when the least significant digit reaches its trigger value.

9. A timing circuit as claimed in claim 8, wherein a control member is arranged to operate the switches by effecting periodic closure of the switches with overlap, and operation of the switches by the control member is recognised by a change in the switch states on adjacent address pulses.

10. A timing circuit as claimed in claim 9, wherein a change in the switch states is effective to reset the counter to its start value when the counter is below its terminal value, and the counter is incremented between changes in the switch states.

11. A timing circuit as claimed in claim 10, wherein the storage means reverts to its rest state when the incrementing counter reaches its terminal value during operation of the control member.

12. A timing circuit as claimed in any one of claims 1 to 11, wherein the first group of cells and the storage means are included in an alterable digital data store.

13. A timing circuit as claimed in claim 12, wherein the alterable digital data store includes a plurality of cells arranged as registers of the incrementing counter.

14. A timing circuit as claimed in any one of claims 1 to 13, wherein the trigger value of the least significant digit is zero.

1 5. A timing circuit as claimed in any one of claims 1 to 14, wherein the alterable data store includes a plurality of first groups of cells.

1 6. A timing circuit as claimed in claim 15, wherein the integrated circuit is arranged to limit the value of the contents of one first group to the difference in value between the contents of two other first groups.

1 7. A timing circuit as claimed in claim 16, wherein operation of the switches has no effect when the limit in difference is reached.

1 8. A timing circuit as claimed in claim 17, wherein control is restored if operation of a switch or the switches, to increment the one first group continues, and the value of the contents of one of the two other first groups is incremented equally.

1 9. A timing circuit as claimed in claim 1 7 or 18, wherein the electrical system is arranged to test for an overlap in time between any two of the first groups when an instruction to change one of the said first groups is entered, and to ignore the instruction when its execution would result in overlap.

20. A timing circuit substantially as herein described with reference to and as illustrated by Figs. 3 to 9 of the accompanying drawings.

21. A timing circuit as claimed in any one of claims 1 to 20, and including a rotary control member arranged to operate the switches.

22. A timing circuit as claimed in claim 21, wherein the rotary control member is arranged to operate the switches by means of relative movement between a magnetic field and components sensitive to the field.

23. A timing circuit as claimed in claim 22, wherein switch operation is by means of a magentic screen.

24. A timing circuit as claimed in claim 23, wherein the rotatable member includes a flywheel.

25. A timing circuit as claimed in claim 1 or 2, wherein push button control members are provided to operate the switches.

26. A timing circuit arranged to record a plurality of times at which operations controlled by the timing circuit occur, and means for providing instructions to enter progressively the said times in the timing circuit, wherein the timing circuit includes an electrical system arranged to test the effect, on recorded times, or each instruction to alter a recorded time before executing the instruction and to ignore the instruction if its execution would result in overlap between any two recorded times.

27. A timing circuit as claimed in claim 26, wherein the timing circuit is arranged to ignore temporarily an instruction that would result in time overlap, and subsequently to execute the instruction and to adjust adjacent times equally to avoid the overlap.