Method for manufacturing a bistable display device with low-voltage microcontroller

Abstract

Method for producing an electrophoretic display device comprising a low-voltage microcontroller. The invention relates to a method for producing a segmented electrophoretic display device (1A) comprising a bistable display (2) operating at predetermined opposing voltages (+dV; -dV) and an electronic circuit (10A, 25) with microcontroller (10, 24) for controlling the display according to a control programme (P). The method is characterised in that it comprises the following steps: - supplying the controller (24), which is different from a specific display controller for a bistable display and configured to deliver voltages (Vsegment), lower in absolute value to the predetermined voltages (+dV; -dV), - compensating said voltages (Vsegment) with at least one compensation voltage (Vcom) to at least reach the predetermined opposing voltages (+dV; -dV). The invention also relates to the corresponding device.

Description

Field of invention.

[0001] The invention relates to a method for producing (or manufacturing) a display device for an electrophoretic or bistable type display.

[0002] The invention relates more particularly to a method and device for controlling an electrophoretic segment display.

[0003] Such displays, targeted by the invention, comprise a layer (or a film) of microcapsules containing colored particles suspended in a fluid or a gas, this same layer being sandwiched between two electrodes: at least a first electrode having the shape of the segment to be displayed a second transparent electrode made of a conductive layer of indium-tin oxide (ITO) for example. Alternative electrodes based on a thin film of carbon nanostructures, silver or copper wires can also be used.

[0004] The invention also relates to electronic products or devices that use the above-mentioned type of display. The display can be used, for example, in smart cards, particularly banking cards or other types of cards having a thin display area and requiring a certain flexibility, USB keys, watches, etc. Prior art.

[0005] Bank cards are currently using integrated systems that allow the display of a dynamic cryptogram (dCVV). This code can vary over time and is displayed using small displays on the back of a bank card. Displays also allow the display of single-use codes such as OTP (one-time password) for secure online transactions.

[0006] There are microcontrollers that integrate specific display drivers for electrophoretic or equivalent screens. For example, the EPSON S1C17F57 microcontroller can perform this function.

[0007] Document US 2010 / 238093 A1 describes a control system for a bi-stable display which comprises a source and gate electrode controller and a common electrode controller.

[0008] Document US 2008 / 238900 A1 describes a control system for a bi-stable display that converts a digital input into control signals for the segments and the common electrode.

[0009] Document US 9,424,797 B1 describes an integrated circuit for controlling a bi-stable display. Technical problem.

[0010] Some display smart cards, such as dynamic cryptogram cards (DCVV), require a bistable electrophoretic display due to the need for permanent display and power consumption constraints.

[0011] Electrophoretic type displays require a specific driver or microcontroller because the absolute voltage required to drive them cannot generally be provided by standard type microcontrollers, especially if the latter is powered by a battery only delivering a voltage of 3V, notably significantly lower than the absolute operating voltage of the display.

[0012] Specific microcontrollers for segment electrophoretic displays are still not very widespread and therefore remain more expensive.

[0013] The invention aims to propose a more economical method for producing electrophoretic display control devices that can replace specific control microcontrollers.

[0014] Alternatives to the invention proposed below by the inventor have the following disadvantages: A possible alternative would be to power the microcontroller with 2 lithium batteries in series to raise the voltage to 6V. This solution has the disadvantage of increasing the cost of the battery and the space occupied by it; Another alternative would be to increase the voltage of the lithium battery from 3V to 5V to power the microcontroller, but due to the thickness constraints of the board, a DC-DC converter solution, if possible without inductance, should be used.Such a solution would use a capacitance-based charge pump, but the resulting efficiency and current increase would lead to poor power consumption performance and thus reduce battery life; Using a standard microcontroller combined with an external display controller would lead to having two circuits and therefore be more expensive; Finally, the electrophoretic display controller function could be added with a microcontroller and program memory (Flash, ROM) in an ASIC, but developing such a circuit is relatively expensive.

[0015] The current market offer for a microcontroller integrating a driver for an electrophoretic segment display is not widespread, which makes it difficult to diversify supply sources. Summary of the invention.

[0016] The invention proposes a simple and inexpensive method for manufacturing / producing a device with a segment electrophoretic display.

[0017] The invention also provides a method / program for controlling an electrophoretic segment display.

[0018] In the principle of a preferred embodiment, the invention provides standard components (not specific to the aforementioned bistable displays). It provides a common or standard microcontroller [having a maximum output voltage lower than the minimum operating voltages, in absolute value, of the display, a programmable memory, preferably flash and integrated into the microcontroller, some external components and a specific control program (described later)]. This type of microcontroller preferably chosen by the invention is distinct from a specific display controller for a bistable display, in particular an electrophoretic segment display.

[0019] The microcontroller is preferably also powered by a so-called low voltage, lower in absolute value than those required to drive the display. In its preferred application, the microcontroller is powered by a voltage of 3V (V = volts) or close to 3V and includes input / output ports (GPIOs) having an output voltage excursion of 0 to 3 volts. The target display has a minimum operating voltage in absolute value of 5 volts.

[0020] A remarkable point of the preferred embodiment of the invention lies in a specific design of a generator, here in the form of a charge pump, making it possible to supply +5V and -2V on a common electrode of the display. This generator can be controlled directly by the microcontroller with only two input / output ports having a voltage excursion between 0 and 3V.

[0021] To this end, the invention relates to a method for producing an electrophoretic segment display device according to claim 1.

[0022] The device thus configured makes it possible to control a bistable display at low cost, with an inexpensive (standard) microcontroller, the output voltages being supplemented by additional voltages (or potentials) generated in particular using a circuit of discrete components such as capacitors, diodes and transistors.

[0023] According to other characteristics: The control program comprises instructions configured to control said voltage generator so as to provide said compensation; The voltage generator is configured to provide voltage values ​​(+5; -2) volts. The microcontroller is configured to provide a first pair of voltages (+3; 0) volts. The microcontroller comprises input / output ports that can be controlled individually with a state “0”, “1” and high impedance (HIZ) and including a program memory.The program provides values ​​of (-5V, +5V) to control a color switch of the segments or the background of the display and voltage values ​​equal to (-2V, +2V) to maintain the colors of the segments (or the background); The program (P) can provide for the successive sequences (or steps): homogenization into a uniform color of all the segments including the background in black or white with a duration of 5 time units; inversion of the uniform color of all the segments including the background in white if previously black or in black if previously white with a duration of 7 time units; updating of the segments which require it in white if previously black or black if previously white with a duration of 5 time units.

[0024] The invention also relates to a segment electrophoretic display device according to claim 8.

[0025] Thus, the invention makes it possible to simply use a common low-voltage microcontroller which is not intended to drive a bistable electrophoretic segment display, by supplementing it with a generator and a few discrete electrical / electronic components. The microcontroller preferably comprises a control program (P) configured to supply the voltages at times and for durations in accordance with a balanced control scheme so that the average value of the voltage seen from each of the segments tends towards 0; The microcontroller comprises a control program (P) to supply the voltages at times and for durations in accordance with a balanced control scheme so that the average value of the voltage seen from each of the segments is close to 0 volts. Brief description of the figures.

[0026] There figure 1illustrates a schematic cross-section of a bistable ink capsule display among those usable by the invention; The figure 2 illustrates a display in top view having three areas of digital characters formed by segments as used in a preferred embodiment of the invention; The figure 3 illustrates a display object with display device, conforming to those covered by the invention and in the form of a smart card; The figure 4 illustrates a possible electrical and / or electronic circuit diagram of the object with display device of the previous figure; The Figure 5 illustrates an electronic circuit for controlling a digital character zone of the display in accordance with the preferred implementation or embodiment of the invention; The figure 6 illustrates an exemplary embodiment of the voltage generator 26 of the circuit of the previous figure, said generator being here, in the form of a hybrid charge pump; The figure 7 illustrates recommended (or preferred) intermediate color and / or image steps and / or transitions of the display device, in accordance with the preferred embodiment of the invention; The figure 8 illustrates the different elementary stages of the process (and / or program P) for controlling the display device, the recommended (or preferred) transitions of which comply with the figure 7 . Description.

[0027] To the figure 1 , an electrophoretic bistable display 2 (or display complex) (also called “ePaper” or electronic paper) for device 1 ( Fig. 3 And 4 ) with display according to a preferred embodiment of the invention comprises a film 5 of microcapsules containing ink, in particular white 5B and black 5N, suspended in a fluid 5C and sandwiched between an ITO layer 4 or transparent electrode and other electrodes constituted by a printed circuit 6 carried by a substrate 6A here flexible.

[0028] The ITO layer is attached to (or supported by) a transparent polymer substrate 3. The printed circuit facing the microcapsules contains as many electrodes as segments and the shape of each electrode defines the shape of each respective segment. Finally, a connection is made between each segment and the display connector. The assembly comprising the transparent polymer 3, the ITO layer 4, the layer 5 of microcapsules 5C and a layer or printed circuit 6, forms the display complex 2.

[0029] The display particles 5B, 5N here are electrically charged and move in the microcapsules 5 depending on the voltage which is applied on the one hand to the transparent conductive layer 4, on the other hand to each of the segments of the conductive layer 6B of the flexible printed circuit 6.

[0030] Returning to the figure 1, the display 2 comprises a common electrode 18 arranged on the printed circuit 6 and electrically connected to the transparent conductive electrode 4 via an adhesive or conductor 19, in particular of the anisotropic type or not.

[0031] The printed circuit 6 comprises conductive control (or command) zones 20 and 21, 22, 23 corresponding respectively to a background zone 20 of the display and segment zones 21, 22, 23; The segment zones display the information in a segment color contrasting with the color of the background zone.

[0032] The printed circuit 6 may preferably contain a circuit for driving the display layer or contain at least conductive driving tracks or areas 6B intended to have an electrical polarity to influence the display layer 5.

[0033] Depending on the voltage difference (dV in volts) applied across the common electrode and the segment conductive areas, the polarized particles of the capsules will be concentrated in the upper and lower part of the capsules according to their respective polarity. All segments have a common electrode 18 (connected to the transparent conductive layer 4).

[0034] By convention in the description, the term "volt" can also be designated by (V) and the numerical / digital values ​​"0", "1" when they are enclosed in quotation marks. The numerical / digital values ​​"0", "1" correspond respectively to the voltage values ​​0 volts (or 0V) and +3 volts (or +3V).

[0035] To figures 2, 3 And 4 , the electrophoretic type display 2 is illustrated in top view; It is integrated, in the example ( figure 3), in an electronic object (or device) 1 with an intelligent display device or circuit 2 (and with a microprocessor). The object 1 is in the form of a chip card, particularly a banking card.

[0036] The display 2 is connected to an electronic display circuit 1A integrated in the card body 1 (not visible on the figure 3 ). The assembly comprising the electronic display circuit 1A and the display 2, forms, comprises or constitutes a display device 25 ( Fig. 4 and 5 ).

[0037] Alternatively, the display device 25 (or display circuit 1A) of the invention can be used for electronic products or devices requiring a bistable display which allows the display of indicators by graphic symbols or alphanumeric characters such as watches, toys, status indicators, etc. and being powered by a voltage lower than 5V in particular. The display device 25 (or display circuit 1A) can be an electrical and / or electronic subassembly (insert or “inlay”) intended to manufacture one of the aforementioned devices comprising at least one display area or display 2.

[0038] Likewise, the display device 25 (or display circuit 1A) may be a module or an insert (intermediate product) ready for use or intended to be inserted or inserted / connected into another body or support. It may comprise at least the display area, one or more connection or interconnection components and a printed circuit with integrated circuit components, in particular for controlling the display layer.

[0039] There figure 4 illustrates an electrical / electronic circuit C of the smart card 1 of the figure 3 ; Circuit C comprises the display 2 connected to the electronic circuit 1A comprising a microcontroller 24 for controlling (or piloting) the display of information on the screen 2.

[0040] The circuit C may comprise a radio frequency interface comprising an NFC radio frequency controller (11) and an antenna 12, connected to the microcontroller 10, a real time clock 15 (RTC), a battery 9, and where appropriate a switch button. The card 1 may comprise a smart card module 17 combined with electrical and / or contactless contacts with a radio frequency antenna 13. To the Figure 5, is illustrated, the display device 25, produced according to a production (or manufacturing) method corresponding to a first preferred mode of implementation and which may be suitable for constituting / replacing the microcontroller circuit 1A of the previous figure; This device comprises a bistable display 2, of one of the types referred to previously (electrophoretic with segments 1A); the bistable display 2 operates or is controlled under predetermined minimum supply (and / or control or piloting) voltages opposite, positive and negative (+dV; -dV); the device 25 comprises an electronic display circuit 1A with microcontroller 24 for piloting the display according to a piloting program (P) included here in a program memory of the microcontroller; In the example, the display is a 3-digit electrophoretic type display with segments (elnk corporation ref: SC004221) although only one digit is illustrated, the principle can be applied to several digits).The operating and / or piloting (or control) voltage is between 5 and 15 volts and between -5 and -15 volts; In other words, to switch the shade of a segment or of each capsule, it is necessary to apply a voltage difference, between the common electrode 4 (or 18) and the piloting or control electrode of the background or of a segment 20 - 23 of at least +5 volts (+dV) to change color and of at least -5 volts (-dV) to return to the initial color; In accordance with this preferred embodiment, the method comprises the following steps: a) providing a microcontroller 24 configured to deliver voltages (which may depend on the power supply source 9), lower in absolute value than the predetermined voltages (+dV; -dV), b) compensation of the voltages delivered by the microcontroller to at least reach said opposite predetermined voltages (+dV; -dV) required for operation.The microcontroller 24 selected for the invention in step a) is configured to deliver a first display control voltage lower than the aforementioned minimum voltage of 5 volts; In the example, the (standard) microcontroller 24 operates at a supply voltage equal to (or of the order of) 3 volts and is capable of delivering to input / output ports a voltage whose voltage excursion is (or of the order of) 0 to 3 volts. It is designed to be powered at 3 volts by a battery 9.

[0041] Generally speaking, a voltage can be considered equal to a value within the meaning of the present application when it is close to 10% of this value, or even 5% preferably. Thus a voltage between 2.7 volts and 3.3 volts is considered to be equal to 3 volts.

[0042] The microcontroller also includes a plurality of output interfaces; here in the example illustrated, it includes general purpose input / output (GPIO) ports from 1 to 10 (GPIO1 - GPIO10). The output ports GPIO4 to GPIO10 are each connected to their respective segment marked a to f (and corresponding to the conductive areas 21-23 of the printed circuit 6, to drive them). Similarly, the output port GPIO3 is connected to the conductive area 20 corresponding to the bottom of the display screen 2.

[0043] With this microcontroller 24 selected for the invention, the GPIO ports can only deliver a maximum voltage of +3 volts to the different segments of the display, which is insufficient to activate the 5C capsules and the color changes of the different display areas (background and segments 20-23).

[0044] At most, this microcontroller 24 could provide a voltage of 0 volts to the common electrode and +3 volts to a segment (or background) or a voltage dV = +3V and conversely a voltage of +3 volts to the common electrode and 0 volts to a segment (or background) or a voltage dV = -3 volts. Therefore, a voltage of 2 volts in absolute value is missing to allow operation of the display. The invention makes it possible to provide this missing voltage (or potential) by at least one compensation voltage (or potential) of at least 2 volts).

[0045] A (standard) MCU 24 microcontroller suitable for the invention preferably comprises the following functions. The normal functions of a CPU microprocessor (the number of bits does not matter); GPIO input / output ports; Preferably these inputs / outputs are individually configurable: input or high impedance (HIZ), output (“push-pull” or totem pole) (“1” or “0”)

[0046] Preferably, the microcontroller should allow each GPIO port to be individually configured in HIZ, as a digital value of "1" or "0" (equivalent to 3 volts and 0 volts respectively). The microcontroller should preferably have at least as many GPIO ports as segments needed, plus four additional GPIO ports (respectively for the background area 20, the transparent common electrode area 18 and two ports for controlling the charge pump). For example, for a 3-digit dCVV display (dynamic cryptogram - Dynamic Card Verification Value): it is advisable to have (7x3) + 2 + 2 = 25 GPIO ports; A program memory (but it can be external); Optionally, the microcontroller can have timers for easier management of the indicated durations T1, T2, T3 but are not essential, since they can be substituted, for example, using a simple waiting loop.

[0047] Today, most microcontrollers (CPUs) support all of the above functions.

[0048] To make the display functional, the invention provides step b) above of compensating the voltages from the microcontroller to at least reach said opposite predetermined voltages (+dV; -dV) required for operation.

[0049] In the example, the invention therefore provides and adds a second voltage to the first voltage of +3 volts to provide at least the minimum voltage required (in this case +5 volts). This is preferably achieved with the generator circuit 26 described below ( fig.6 ).

[0050] According to a preferred embodiment or implementation, the invention provides a particular voltage source allowing voltage / potential compensation (or voltage difference compensation) obtained according to the table below.

[0051] In the example, the source is therefore a voltage generator 26. This generator is preferably controlled by the microcontroller 24; for this, the latter includes output ports GPIO 1 and GPIO2 connected to this voltage generator 26.

[0052] This generator 26 is powered like the microcontroller by a battery 9 which is preferably the same as that of the microcontroller (+3V). The voltage generator also has an output 27 (Vcom) which is connected to the transparent common electrode 18.

[0053] Thus, thanks to an adapted program P, supplied to the standard microcontroller 24, preferably in an EEPROM or flash memory internal (or not) to the microcontroller, the invention proposes to control the display 2. This control occurs as if the display device 25 had a dedicated microcontroller capable of delivering a sufficient control output voltage of at least 5 volts.

[0054] Preferably, the invention provides according to this program P (or convention), that a single voltage, positive or negative (for example +5 and -5 volts), causes a change of color in the display.

[0055] Depending on the preferred mode, the microcontroller 24 applies the positive voltage values ​​+0 or +3 volts (which it is capable of delivering normally) to the segments (or background) according to a program P for managing the voltage of the segments (or background). The charge pump 26 delivers at output 27 and applies the voltage values ​​Vcom = +5 volts or (-2) volts to the common electrode 18 also according to the program P for managing the voltage / potential of the electrode 18.

[0056] We thus obtain a first control potential difference of -5 volts "dV = 0 - 5" by putting the lowest potential value of the microcontroller (0 volts) on the segments or background; this last voltage is compensated (or supplemented) by a voltage (or potential) of +5 volts placed on the electrode 18 and obtained by a charge pump 26.

[0057] We also obtain a second difference in control potentials of +5 volts "dV = 3 - (-2)" by putting the highest potential value of the microcontroller (+3 volts) always on the segments (or background), this last potential value being compensated (or completed) by a voltage (or potential) Vcom of - 2 volts placed on electrode 18, obtained by the charge pump.

[0058] With this preferred compensation scheme, it is possible to drive the display with the voltages required for display operation.

[0059] In the example, this generator 26 comprises (or consists of) a charge pump (detailed later with reference to the figure 6 ).

[0060] The operation of the display control is described in relation to the steps in the flow chart. figure 7 which may correspond to steps of a program P (or hard-wired logic circuit) provided in the microcontroller to control a segment or background zone 20.

[0061] Given a limitation of the output voltage excursion here in the example from 0 to 3V for the output ports (GPIO1 to GPIO10), this preferred embodiment of the invention provides possible voltages for updating the display, reported in the table below: Vcom voltage on common electrode (volts) Vsegment voltage on segments (or background) GPIO3 to GPIO10 (volts) Voltage difference (dV) (Vsegment - Vcom) on 5C capsules (volts) + 5 + 3 3 - 5 = - 2 + 5 0 0 - 5 = - 5 - 2 + 3 3 - (-2) = + 5 - 2 0 0 - (-2) = + 2

[0062] Another remarkable point of this preferred embodiment of the invention lies in the low sensitivity of the display when the absolute value of the voltage difference dV, between the segments (or the background) and the transparent common electrode (or 18), is less than 2.5 volts.

[0063] It can be considered that this low voltage has no significant effect on the current state of the segment (white or black).

[0064] Thus, the low sensitivity is advantageously used by this preferred embodiment of the invention for a particular control scheme or principle below: High voltage dV offsets (-5V, +5V) can be used to drive a segment color change (black to white or vice versa); Low voltage dV offsets (-2V, +2V) can be used to maintain the segment color (black to black or white to white).

[0065] For an electrophoretic type display, it is necessary to have a specific waveform (or sequence) method to avoid artifacts or "ghost" effects (due to interference between adjacent areas of the screen that have different colors). A main artifact can be avoided by switching all segments and the background from white to black or vice versa.

[0066] To the figure 7 , a recommended "waveform" method from Eink Company is used, to avoid the above problems is called "Global White Black Waveform". The values ​​of the voltages applied to the common electrode 18, segments and background, appearing on the right ordinate of the diagram, correspond to those of the preferred embodiment of the invention.

[0067] To avoid damaging the display, it is preferable to have a so-called balanced control mode. This means that the average voltage between the common electrode 18 and each of the segments must tend towards 0, over all the cycles of the display during its entire lifetime. An imbalance may, however, occasionally exist for the display of a given color, but over a cycle consisting of switching from one color to another and then returning to the initial color, the average value of the voltage applied for the segment concerned must tend towards 0.

[0068] The preferred method of "global white-black waveform", involves a specific duty cycle on the display cycle formed by T1+T2+T3 ( figure 7 ). Four scenarios that can occur simultaneously during a display cycle should be considered: 1- Maintaining the segment in Black (curve 1): T1: period of 5 / 17, switching from Black to White; T2: period of 7 / 17, switching from White to Black; T3: period of 5 / 17, configuration not resulting in a change of color. 2- Maintaining the segment in White (curve 2): T1: period of 5 / 17, configuration not resulting in a change of color. T2: period of 7 / 17, switching from White to Black; T3: period of 5 / 17, switching from Black to White. 3- Switching the segment from Black to White (curve 3): T1: period of 5 / 17, switching from Black to White; T2: period of 7 / 17, switching from White to Black; T3: period of 5 / 17, switching from Black to White. 4- Switching of the segment from White to Black (curve 4): T1: period of 5 / 17, configuration not causing a change of color; T2: period of 7 / 17, switching from White to Black; T3: period of 5 / 17, configuration not causing a change of color.

[0069] This specific duty cycle allows balanced control of the display, the calculation of which is described below.

[0070] Similarly, it is also possible to use the "Global Black White Waveform" method which consists of inverting the two T1 and T2 sequences.

[0071] A complete prototype was successfully built using an ST development board (STM8 Discovery with STM8L152C6 MCU, breadboard and discrete components for the charge pump circuit, a 3-digit EPD display from the company "Eink".

[0072] A program or microcode P was developed to program the microcontroller 24 to display the 3 digits on the display screen.

[0073] To the figure 8, an overview of this program P is described in relation below, for the switching of a segment; It can be extrapolated to other segments and ports.

[0074] The microcontroller 24 receives information, in particular an OTP number to be displayed on the display (the OTP information includes or requires, for example, at least one switching of a segment b among the seven segments included in the display to form a digit). This segment b is connected to the GPIO4 port ( Fig. 5 )

[0075] The microcontroller can know the current bistable state of segment b in particular by consulting either directly a memory listing the last state of the black or white segment or indirectly by means of information external to the microcontroller.

[0076] At step 100 of the method (or program P), the microcontroller deduces that the segment is in a “white” state and / or which corresponds to a set of instructions previously issued and having led to a voltage difference having caused a switching to white.

[0077] The program can then switch the segment color to black 200 or keep the segment color white and switch other segments of the display 250 to black 252 or white 251.

[0078] Once the segment is switched to black, the program can switch the segment color back to bank 300 or it can keep the segment color black and switch other segments of the display 260 to black 262 or white 261.

[0079] Once the segment is switched back to white, the program can return to the initial sequence and can restart a new sequence.

[0080] Otherwise, the microcontroller can provide a "reset" step or zeroing (white or black) of all the segments regardless of knowing their initial state. This procedure is particularly useful during the first initialization of the product or the initial state of the segments is not necessarily known.

[0081] The microcontroller's P program is configured to drive the ports, depending on the sequence, as follows: For the segment toggling from white to black (200), the microcontroller's P program configures the GPIO4 port to a level "1" or (+3V), the GPIO1 port to a logic level "1" or (+3V) and generates a square clock signal of 1kHz and levels 0 and +3 V on the GPIO2 port, which generates a Vcom voltage of -2V at output 27 of the charge pump 26 and a Vsegment voltage of +3V.

[0082] This results in a voltage difference dV of +5V sufficient to switch the visible color of the capsules forming segment 4 from a “white” color state to a “black” state.

[0083] To switch the segment from black to white (300), the microcontroller's P program configures the GPIO4 port to a "0" level, i.e. (+0V), the GPIO2 port to a logic "0" level, i.e. (+0V) and generates a 1kHz square clock signal with levels 0 and +3V on the GPIO1 port, which generates a Vcom voltage of +5V at output 27 of the charge pump 26 and a Vsegment voltage of +0V.

[0084] This results in a voltage difference dV of -5V sufficient to switch the visible color of the capsules forming segment 4 from a “black” color state to a “white” state.

[0085] To maintain the color and switch the other segments from white to black (252, 262), the P program of the microcontroller configures the GPIO4 port to a level "0" or (+0V), the GPIO1 port to a logic level "1" or (+3V) and generates a square clock signal of 1kHz and levels 0 and +3 V on the GPIO2 port, which generates a Vcom voltage of -2V at output 27 of the charge pump 26 and a Vsegment voltage of +0V.

[0086] This results in a voltage difference dV of +2V which maintains the current color of the segment and allows the capsules forming the other segments to switch from a "white" color state to a "black" state if the corresponding GPIO is at a logic level "1" i.e. (+3V).

[0087] To maintain the color and switch the other segments from black to white (251, 261), the P program of the microcontroller configures the GPIO4 port to a level "1" or (+3V), the GPIO2 port to a logic level "0" or (+0V) and generates a square clock signal of 1kHz and levels 0 and +3 V on the GPIO1 port, which generates a Vcom voltage of +5V at output 27 of the charge pump 26 and a Vsegment voltage of +3V.

[0088] This results in a voltage difference dV of -2V which maintains the current color of the segment and allows the capsules forming the other segments to switch from a "black" color state to a "white" state if the corresponding GPIO is at a logic level "0" i.e. (+0V).

[0089] At the end of the different driving sequences above, the different ports used for driving the display GPIO1, GPIO2 & GPIO4 in a preferred mode, can be configured to “0” (0 V) or in a high impedance state (HIZ).

[0090] For each case, the microcontroller can preferably (or not) save the change of state of the segment(s) in memory for later consultation.

[0091] To the figure 6 An electrical diagram and operation of the charge pump is illustrated: The charge pump 26 constitutes a voltage generator in accordance with the preferred embodiment of the invention; The electrical / electronic diagram comprises two stages (or sub-parts 28, 29) having respectively an input GPIO 1, GPIO2 and a common output Vcom: Stage 28 (or doubler circuit), relating to the GPIO1 input, includes a P-type field effect transistor Q1 connected with diodes D1, D2 and capacitors C1, C3; Stage 29 (or inverter circuit), relating to the GPIO2 input, includes an N-type field effect transistor Q2 connected with diodes D3, D4 and capacitors C2, C4.

[0092] The charge pump is therefore based here preferably on the combination of a voltage doubling electrical circuit 28 and a voltage inverter electrical circuit 29 which can be alternately switched using two MOS FET transistors and whose output voltage from one or the other charge pump is combined on a single line.

[0093] For displaying an electrophoretic segment, no multiplexing is possible, meaning that each segment must be driven individually by a GPIO port of the microcontroller.

[0094] Two other pins are needed: one (20) for the background of the display (zone 20 visible other than a segment, but considered as a segment for control) and the other 18 for the common of the segments.

[0095] An electrophoretic display is a bistable display, meaning that only a change of state needs to be controlled. The basic operation is as follows: when a voltage of +5V is applied between a segment and the common electrode, the segment turns black; and when a voltage of -5V is applied between a segment and the common electrode, the segment switches to white; Otherwise, when no voltage is applied, the segment remains stable by preserving its current state (white or black) or when the absolute value of the voltage is less than 2.5 volts.

[0096] In the embodiment, segments 21, 22, 23 and bottom 20 are directly connected to the input / output ports of the microcontroller having a voltage excursion of 0 to 3V.

[0097] A Vcom voltage, coming from the charge pump and having a voltage excursion of -2V or +5V with respect to ground, is applied to the transparent common electrode 18 of the segments. This is a viable design since these two voltage values ​​cannot be applied directly to or generated by the input / output ports of the microcontroller (limiting the output voltage excursion between 0 and 3V).

[0098] The components used in the realized example include a transistor Q1: N-MOS FET CSD13381F4; a transistor Q2: P-MOS FET CSD23381F4; Four capacitors C1-C4: 100 nF 10V; Four diodes D1-D4: RB521. The operation of the charge pump is as follows :

[0099] The charge pump output voltage Vcom = +5V when: A 1KHz clock with a 50% duty cycle is generated on GPIO1; GPIO2 is set to “0” (0V);

[0100] In this case, transistor Q2 is in the off state and stage 29 including capacitor C2 and diodes D1, D2 has no effect on the output Vcom. On the other hand, stage 28 including components Q1, C1, C3, D1 and D2, forms a voltage doubler and VCom reaches 5 V due to the voltage drop across diodes D1 and D2 in the forward direction. The output voltage of the charge pump Vcom = -2V when: GPIO1 is set to "1" (+3V); A 1KHz clock with a duty cycle of 50% is generated on GPIO2.

[0101] In this case, transistor Q1 is in the off state and stage 28 comprising components C1, D1, D2 has no effect on the output Vcom; On the other hand, stage 29 comprising components Q2, C2, C4, D3 and D4 constitutes a voltage inverter and the output voltage VCom reaches -2V due to the voltage drop in diodes D3 and D4 in the forward direction.

[0102] Alternatively, another possible embodiment of the generator may be a generator system comprising two independent charge pumps that can be activated or deactivated by the microcontroller and generate respectively +5V and -2V and one or the other of the voltages would be selected by an electronic switch. However, such an embodiment would be more complex and expensive mainly due to the switch (which is avoided in the preferred mode). There figure 7 illustrates recommended (or preferred) intermediate steps and / or transitions of color and / or images of the display device, in accordance with the preferred embodiment of the invention detailed below. For the switching of color or state of the segment zones of the display, the invention prefers to use a particular cycle of transition of states of the segments (and / or the background) (drawing 43) for switching the display zones from black to white or vice versa.

[0103] Drawings 41, 42 and 43 ( Fig. 7 ) illustrate the different segment state change curves for switching from the number "1" to the number "2". Each segment color switching (or holding) curve referenced b, f, c, e is numbered respectively from 1 to 4 as follows: 1 for holding segment b from black to black; 2 for holding segment f from white to white; 3 for switching segment c from black to white; 4 for switching segment e from white to black.

[0104] In drawings 42 and 43, the intermediate transitions of color of the segments and / or of the background (or of state of the segments or of the background) taking place to carry out the operation of changing the number from 1 to 2 are illustrated in images. A complete display cycle comprises the succession of 3 main stages: a first step of setting all segments (including the background) which are black to white for a recommended time T1 equal to 5 time units (i.e. 500ms, the unit being equal to 100 milliseconds); followed by a second step of setting all segments (including the background) to black for a time T2 equal to 7 time units (i.e. 700ms); and ending with a third step of setting the segments displaying the number “2” to the final black color for a time T3 equal to 5 time units (i.e. 500ms).

[0105] Drawing 43 ( fig.7 ), also illustrates the different voltages required of the segments and the common electrode (ITO) for each transition step illustrated in drawing 42 (and in accordance with the preferred embodiment of the invention): “Vcom” for the transparent common electrode 18; “V segment” for the relevant segment a to f; as well as the resulting voltage difference (dV) across the segment.

[0106] On the left, on the ordinate, are the electrical zones concerned, respectively, the transparent common electrode 18 (or ITO), segment b which must remain in black color, segment f and the background which must remain in white color, segment c which must switch from black to white and segments a, d, e & g which must switch from white to black.

[0107] On the right, on the ordinate, are indicated the applied voltages of +5 volts, +3 volts, 0 volts -2 volts and -5 volts to each electrical zone mentioned above.

[0108] The invention may preferably provide, for controlling the display, the steps and / or image or color transitions indicated and respecting the durations and voltages described on the figure 7 .

[0109] These above steps and / or transitions are implemented using a corresponding program P, recorded in the memory of the microcontroller 24 of the Figure 5(or external memory to the microcontroller). This program is executed by the microcontroller to directly control or drive the inputs of display 2 (via the corresponding output ports “GPIO3 to GPIO10” of the microcontroller) by a voltage signal equal to 0 or +3 volts.

[0110] The P program also controls, via the GPIO1 and GPIO2 output ports of the microcontroller, the Vcom voltage of the transparent electrode (18), via the generator 26, to obtain a Vcom signal of +5 volts, - 2 volts or 0 volts.

[0111] Thus, the invention makes it possible to increase the differential voltage Vsegment-Vcom applied to segments a to f and / or the bottom while using input / output ports having a voltage excursion from 0V to +3V. Compensation to obtain a sufficient potential difference for driving is carried out by injecting a voltage / potential of +5V or -2V onto the common electrode Vcom 18.

[0112] This results in dV voltage deviations on 5C ink capsules that can reach +5V or -5V to change the color and dV voltage deviations that can reach +2V or -2V to maintain the color.

[0113] Checking the voltage balance of the control signal in relation to the figure 7 .

[0114] The signal is said to be balanced if the average voltage value is zero for the sequence of the different phases over a complete cycle. A complete cycle includes a change of color and a return to the initial color. 1) Black to black: Integrating the signal voltage over the period T1 + T2 + T3 to switch from black to black: (-5 x 5) + (5 x 7) + (- 2 x 5) = 0; 2) White to white: The integration of the signal voltage over the period T1 + T2 + T3 to switch from white to white: (-2 x 5) + (5 x 7) + (- 5 x 5) = 0; 3) Black to white:Integrating the signal voltage over the period T1 + T2 + T3 to switch from black to white: (-5 x 5) + (5 x 7) + (- 5 x 5) = -15; 4) White to black: Integrating the signal voltage over the period T1 + T2 + T3 to switch from white to black: (-2 x 5) + (5 x 7) + (- 2 x 5) = 15.

[0115] For a complete cycle, the invention alternates cycle 3) black to white, then cycle 4) to switch from white to black with possibly the insertion of steps 1) and 2). The integration of the signal voltage of the respective periods T1 + T2 + T3 to switch from black to white and of the periods T1 + T2 + T3 to switch from white to black: dT = -15 + 15 = 0. The insertion of steps 1) and or 2) to maintain the black color or the white color does not modify the balance of the signal, because the integration of the signal on T1 + T2 + T3 for these 2 steps is zero.

[0116] Therefore, signal balance (which consists of having an average value of zero voltage over a complete cycle) is achieved by this control scheme and transitions of the figure 7 according to the preferred mode.

[0117] The state diagram of the figure 8 illustrates an example of the display method (or program) in accordance with an elementary embodiment of the invention for switching the segment from one color to another.

[0118] At step I00, the program P starts for the first time and has therefore not yet performed any segment control sequences. Here the initial state of the segments is assumed to be white.

[0119] In the absence of knowledge of the history, the program can command a preliminary "reset" (or erasure) of the display by switching all the segments and / or the background prior to a display command, to an all-white or all-black color state. This can occur in particular when switching on for the first time or following a battery change, for example.

[0120] At any time, the program can switch a segment from white to black 200 or from black to white 300.

[0121] If the display includes several segments, additional steps of maintaining the color of segment 250, 260 can be performed, so as to have different colors between the segments. 2 sequences are then possible: Maintaining the segment color and switching other segments from black to white (251 & 261) Maintaining the segment color and switching other segments from white to black (252 & 262)

[0122] Depending on the sequences, the P program configures the GPIOs according to the previous description.

[0123] At any time (200, 250, 260 & 300), the program can be suspended after the execution of a control sequence and the memorization, preferably, of the current state of the segments. A history of the states of the segments can thus be kept in the memory of the microcontroller or external memory for later consultation or even be recalculated according to parameters internal or external to the microcontroller. The program can thus resume the next appropriate cycle thanks to the knowledge of the current state of the segments which has been memorized.

[0124] After executing a control sequence, the display then retains the colors of each of the segments, the latter being bistable.

[0125] These steps of controlling the display device may be in accordance with steps of the program P, in particular for the succession of sequences and the respective duration of the sequences recommended according to the preferred mode of the invention to avoid the artifacts described previously. The preferred mode of control may comprise the successive sequence of the 3 sequences (steps or transitions): 1- Homogenization in a uniform color of all segments including the background in black or white with a duration of 5 time units. 2- Inversion of the uniform color of all segments including the background in white if previously black or in black if previously white with a duration of 7 time units. 3- Update of the segments that require it in white if previously black or black if previously white with a duration of 5 time units.

[0126] The invention also has the advantage of allowing flexibility in component procurement by avoiding dependence on a specific microcontroller integrating an electrophoretic display driver (electrophoretic drivers or EPDs integrated into the microcontroller are not widespread). It allows for cost reductions since standard microcontrollers with additional external components can be more competitive than microcontrollers with integrated electrophoretic drivers.

[0127] This control system has the advantage of using standard components whose thicknesses are compatible with a smart card type form factor.

[0128] The invention can be applied to any other electrical device using segment displays (such as digital, alphanumeric displays or indicator lights) and having a display control microcontroller designed to deliver to output ports a maximum voltage lower in absolute value than the operating voltage of the display.

[0129] In particular, any device with a bistable electrophoretic segment display, powered in particular by a voltage lower than +5 volts, could implement the invention.

Claims

1. A method for producing a segmented electrophoretic display device (25) comprising a bistable display (2) operating with predetermined opposite voltages (+dV; -dV) and an electronic circuit (25) with microcontroller (24) for controlling the display according to a control program (P), the method comprising the following steps: - supplying said microcontroller (24), the latter not being a specific display controller for a bistable display and being configured to deliver voltages (Vsegment) on n input / output ports GPIO1-GPIOn, lower in absolute value than the predetermined voltages (+dV; -dV), the input / output ports of the microcontroller GPIO3-GPIOn being connected directly to conductive areas of the segments of the bistable display (2), and - compensating the voltages delivered to the input / output ports (Vsegment) with at least one compensation voltage (Vcom) to at least achieve said opposite predetermined voltages (+dV; -dV), the method being such that said compensation (Vcom) is effected by means of a voltage generator (26) having an output connected to a common electrode of the bistable display (2), and comprising a hybrid charge pump supplied by the same voltage source as the microcontroller (24) and combining a voltage doubler circuit (28) and a voltage inverter circuit (29), the respective output voltages of the doubler circuit (28) and the inverter circuit (29) being combined alternately on the output (27) of the charge pump (26) connected to a common electrode of the bistable display (2), the voltage doubler circuit being controlled by the microcontroller input / output port GPIO1 and the voltage inverter circuit being controlled by the microcontroller input / output port GPIO2.

2. The method according to the preceding claim, characterized in that said control program (P) controls said voltage generator to supply said compensation voltage (Vcom).

3. The method according to the preceding claim, characterized in that said voltage generator (26) is configured to supply voltage values equal to (+5; -2) volts on a single output (Vcom).

4. The method according to the preceding claim, characterized in that said microcontroller (24) is configured to provide a voltage pair (Vsegment) equal to or close to (+3; 0) volts on input / output ports.

5. The method according to one of claims 2 to 4, characterized in that said program (P) provides voltage values equal to (-5V, +5V) to order a switch in the color of the segments or background of the display, and voltage values equal to (-2V, +2V) to maintain the colors of the segments or background.

6. The method according to one of the preceding claims, wherein the input / output ports GPIO can be individually controlled with a "0", "1" and high impedance (HIZ) state.

7. The method according to one of the preceding claims, characterized in that said program (P) provides for the successive sequencing of the following: - homogenizing all segments, including the black or white background, to a uniform color with a duration of 5 time units; - uniformly inverting the color of all segments, including turning the background to white if previously black or to black if previously white, with a duration of 7 time units; - updating the segments that require it to white if previously black or to black if previously white, with a duration of 5 time units.

8. A segmented electrophoretic display device (25) comprising a bistable display (2) operating with predetermined opposite voltages (+dV; -dV) and an electronic circuit (1A) with microcontroller (24) for controlling the display according to a control program (P), characterized in thatit comprises: - said microcontroller (24), the latter not being a specific display controller for a bistable display and being configured to deliver voltages (Vsegment) on n input / output ports GPIO1-GPIOn, lower in absolute value than the predetermined voltages (+dV; -dV), the input / output ports of the microcontroller GPIO3-GPIOn being connected directly to conductive areas of the segments of the bistable display (2), - a compensation voltage (Vcom) generator (26) configured to compensate for said voltages (Vsegment) and achieve at least said opposite predetermined voltages (+dV; -dV), the compensation voltage generator (26) having an output connected to a common electrode of the bistable display (2), the display device being such that the voltage generator (26) comprises a hybrid charge pump powered by the same voltage source as the microcontroller (24) and combining a voltage doubler circuit (28) and a voltage inverter circuit (29), the respective output voltages of the doubler circuit (28) and the inverter circuit (29) being alternately combined at the output (27) of the charge pump (26) connected to a common electrode of the bistable display (2), p5 I34 p6 I4le voltage doubler circuit being controlled by the input / output port of the GPIO1 microcontroller and the voltage inverter circuit being controlled by the input / output port of the GPIO2 microcontroller.

9. The device according to the preceding claim, characterized in that the microcontroller comprises a control program (P) for supplying the voltages at moments and for durations (T1, T2, T3) conforming to a balanced control scheme so that the average value of the voltage seen from each of the segments is close to 0 volts.

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