text: referring firstly to fig1 and , where it contains , equivalent componentry , fig5 , the circuit is designed to monitor the load connected to the “ iron ” output , and depending on the presence of that load determines the availability of power to the “ board ” output . additionally , the circuit provides user functions via the “ mode ” switch s 1 . there are four modes available . mode 0 is off . this is the default mode that occurs upon the application of ac mains , or may be entered by successive presses of the mode switch . modes 1 , 2 , and 3 are all “ on ” functions . different temperature settings are programmed into each of the mode 1 - 3 settings . three leds ( d 3 , d 4 and d 5 ) indicate the currently selected mode . temperature sensor ts 1 is located within measurement proximity of the board and is used to provide monitoring of the board temperature by the cpu ( u 2 ). the circuit common is connected to the ac mains neutral lead . the line or “ hot ” lead powers the circuit via a thermal fuse physically located with the board in a manner which will protect against thermal runaway which could occur due to a failure of electronic components in the design . surge protector vr 1 protects against transient voltage spikes . the circuit comprised of r 1 , c 1 , d 1 , d 2 and c 2 , provide a reduction of ac mains to a voltage level that can be managed by + 5 volt regulator u 1 . u 1 provides a regulated + 5 volt power source which is used to power the cpu ( u 2 ) and associated components . the cpu ( u 2 ) is a pic microcontroller , type pic16c710 . firmware in the pic &# 39 ; s eprom define the inputs and outputs as well as the mode functions and associated driving of the led display , temperature control of the board and determination of the availability of power for the board and iron heating elements . initially upon connection of the circuit to ac mains , the cpu boots up and waits until the iron , set in an on condition , is detected . at this point power is not supplied to either the iron or board heating elements . additionally , all leds are off . the intended use of the product requires that an iron be plugged into the outlet provided on the board . assuming this is done , and the iron is set to a desired ironing temperature , an ac voltage will be presented to the circuit comprised of r 11 , r 12 and the led side of opto - isolator u 3 . the presence of the av voltage drives u 3 on , causing a low logic level during a portion of the ac cycle at u 2 port rb 5 . the firmware running in the cpu detects the low level on rb 5 and then enables the operation of the mode switch . when the mode switch is advanced ( by pressing it one or more times ) q 2 , a triac , is driven to an on state . this supplies ac mains to the iron . the mode switch hereafter remains enabled during the normal use of the iron . however , after an amount of time passes that suggests that the iron has been turned off or unplugged , all power to both the board and iron ceases and the circuit reverts to an off position . as the iron heats , the user may select the desired board temperature by successive presses of the mode switch . the selected setting is indicated by three leds , d 3 , d 4 and d 5 . a reference voltage is set by resistor which is mounted in close proximity to the board heating element . the circuit which includes ts 1 and rs forms a voltage divider and is connected to cpu port pin ra 0 . this voltage is proportional to the temperature of the board . the a / d converted function of the cpu compares the analog signal voltage present on value is calculated and stored in a cpu register , referred to as “ vtemp ”. vtemp is a number from 00h to ffh that represents the amplitude of the voltage from the temperature sensor that is measuring the temperature of the board . the cpu firmware them compares the valve of “ vtemp ” to high and low limit values set in a pair of registers associated with each of the three active mode settings . if the value of vtemp is larger than then high limit , board heating is disabled . if the value of vtemp is lower than the low limit value selected from that mode then board heating is enabled . heating of the board remains enabled until the vtemp value is greater than the high limit register for the mode setting , or the iron requests power , or if the mode control is changed to a lower temperature setting or set to off . sensing of the status of the iron is done using the circuit which includes opto - isolator u 3 and associated components r 11 , r 12 . when power is called for by the iron , the thermostat internal to the iron connects the heating element of the iron to the ac plug which is plugged into the iron output of the circuit . this presents an ac voltage which after voltage division turns on the led internal to u 3 and provides a low logic level to cpu input rb 5 . this causes the cpu to respond immediately by turning on q 2 , which turns on the iron , while setting q 1 off ( if it was previously on ) and thus removing any power to the board heating element . once q 2 is activated , u 3 is no longer able to detect the state of the iron . this is due to the fact that no potential difference remains across the led of u 3 when q 2 is on . the output of u 3 , connected to cpu port rb 5 , thus goes back to a high position . this would logically be interpreted by the cpu that the iron is in an off state or has been unplugged , and this would result in power being restored to the board heating elements . obviously , the iron would never be able to reach a proper temperature due to the fact that power to the iron would rapidly cycle on and off in an undesirable manner . the firmware solves this problem by cycling q 2 to an off state for the minimum time for the cpu to read the logic state of port rb 5 while q 2 is off . this is done repeatedly over a period of seconds . it can then be determined by the cpu when the iron is no longer requiring power when the conditions of reaching the setting on the iron &# 39 ; s thermostat , or having been turned off , or unplugged from the board are established . the cpu then makes the decision whether or not to turn on q 1 , thus enabling power to the board heating element , if heat is called for by the board thermostat . at any time that the iron calls for power , this is instantly detected by the cpu causing the board power to be disabled and the iron power enabled . r 2 is used to provide current limiting for the three leds , d 3 , d 4 and d 5 . c 3 is a decoupling capacitor connected across the + 5 v buss and common . r 3 provides pull up for cp port rb 0 , which is connected to the mode switch . r 7 , r 8 and r 9 are port pull up resistors . r 21 and c 4 determine the clock frequency of the cpu . r 13 , c 6 and r 14 , c 5 are included for dc isolation from the triac gates . the triacs are driven by a pulse stream which originates from the cpu . referring now to fig2 to 4 , an ironing board with an electrically heated working surface with temperature control , provision for the connection of an electrically heated iron and housing for the present invention electronic power management system situated at the rear is illustrated . the appliance may be optionally powered by the inclusion of a suitably geared motor and worm drive shaft as illustrated . in fig2 , a front view of the upper working surface ( 1 ) of the ironing board is shown with the iron rest ( 2 ) as an integral part of the upper working surface and control housing . a control panel ( 3 ) is located at the rear of the board , the facial panel of the control box containing the mode switch and indicator lights ( 4 ) which indicate the selected temperature of the working surface of the board . located in the centre of the facia panel is a power socket ( 5 ) which is the power source for an electric iron . this location facilitates the use of an iron from either side of the board making it a left or right handed appliance ( 6 ) indicating legs and roller feet to ease transfer from place of storage to place of operation . fig3 illustrates an underside view of the board showing the position of the rear support leg ( 6 ) which is attached to the underside of the board by two hinges ( 7 ) that lock the support leg into a static position . the forward support leg ( 8 ) is pivotally attached to leg ( 6 ) at ( 9 ), allowing the forward leg to move forward and backwards to adjust the horizontal height of the board working surface . to assist movement of the forward leg , support channel assemblies ( 10 ) are located on the underside of the board . guide rollers ( 11 ) are mounted on the upper part of the front support let for movement in the channels , ensuring smooth running when adjustment takes place . adjustment is made by means of a worm drive ( 12 ) attached to the underside of the board . manual horizontal movement is achieved by means of a folding handle ( 13 ) situated at one end of the drive shaft . an alternative means of achieving horizontal movement of the work surface is the inclusion of a small electric motor ( 14 ) sited at the opposite end of the drive shaft to the folding handle . direct control for the motor would be located on the facial panel of the control box , and / or by a remote infra red unit . the work and reduction gear will interlock with the handle and motor by way of a small drive coupling . fig4 illustrates the ironing board in the conventional work position . the electronic load management circuitry is housed within the control box ( 15 ). the circuit board is protected from heat emanating from the iron by a heat insulating shield ( 18 ) below and to the side of the iron rest . the view demonstrates the angle of the recess containing the iron rest platform for ease of use and maximum stability of the iron while in the park position . the board is heated by an electrical element ( 19 ) controlled by the circuitry in the control box .