This article will provide instructions on display driving and the electrical integration of Ynvisible’s e-paper technology. It will introduce both the hardware and firmware needed to operate the displays successfully.

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Quick Facts About Ynvisible's E-Paper Displays

As already mentioned, Ynvisible's printed e-paper displays are ultra-low power. The recommended driving voltage is ±1.5V and one square centimeter active display area requires approximately 1 mJ to activate. This translates to roughly 1-2 µW/cm² for an always-on display.

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The displays are manufactured using roll-to-roll screen-printing and lamination processes. They are non-toxic, ITO-free, and mainly comprised of PET plastic. The plastic substrate and roll-to-roll production means thin, flexible, scalable, and highly cost-effective displays. Get started using Ynvisible's e-paper display kit.

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Background 

Ynvisible’s technology is very simple to drive. This is one of the key differentiators to other e-paper technologies. The GPIOs in most MCUs can drive the displays with a minimal requirement of additional components. Apply a positive voltage across the display segment to turn on and short circuit, or apply a negative voltage to turn off. The voltage should only be applied when the display switches or is being refreshed. There are some different options depending on the use case and system prerequisites that we will cover below. 

Key Points About Display Driving

• Display driving will need to be adapted to the final display design and use case, but the fundamental principles are the same for all Ynvisible displays.
• The displays are direct-driven, one electrode per segment plus one common electrode.
• A positive voltage, in reference to the common electrode, turns ON the display segment.
• A negative voltage (or shortening the work and common electrode) turns OFF the segment.  
• A higher voltage level enables a faster switching speed, while a lower voltage enables a longer lifetime. 
• The typical recommendation is ±1,5V across the segment for a good trade-off between switch speed and long lifetime.  
• Keeping the voltage to a minimum is recommended if switching speed is not an issue. Only 1.2V is sufficient to reach full contrast, and it is possible to shorten (≈0V) the common electrode and the work electrode to turn the segment OFF.

Ynvisible’s Display Driver & Resources 

Ynvisible has developed a Display Driver together with instructions and a library for rapid prototyping and demonstrators. Please check the datasheet for more information, including electrical and timing characteristics. We also offer a 16-pin adapter for convenient flex-to-pin integration.

Circuit Suggestions 

 There are many ways to add the Ynvisible E-Paper Display to a circuit. It typically requires zero or very few additional components. All suggestions are based around an MCU with IOs that can be set to High-Z mode (almost all MCUs have this feature).  

Circuit 1 (voltage regulator circuit)  

 A low pass filter and an operational amplifier are used to create a variable virtual ground on the common electrode. By adjusting the frequency of the PWM signal, the voltage can be adjusted to the desired driving voltage. In this way, the correct voltage can be applied to the segments, independent of the MCU operating voltage. The IOs require a High-Z state to maintain the image between the updates. 

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Circuit 2 (DAC output on common electrode)  

If the MCU has a built-in DAC, it can be used as a virtual ground for the common electrode. The DAC replaces the external components in circuit 1. The IOs require a High-Z state to maintain the image between the updates.

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Circuit 3 (2-level variable common electrode)  

A voltage divider is created with R1 and R2. Setting IO0 to HIGH and IO1 to LOW, a first voltage level is achieved on the common electrode. A second voltage is achieved by setting IO0 to LOW and IO1 to HIGH. The IOs require a High-Z state to maintain the image between the updates. 

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Resistor suggestions for different supply voltages to achieve ±1,5V driving on different voltage levels:  

Circuit 4 (digital outputs)  

This approach does not require any external components. The voltage will be limited to the supply voltage of the MCU in use. The ideal driving voltage for the display is ±1,5V. Operating voltages of 1,8 V and higher can be considered if the lifetime requirements are limited. Adding a resistor between IO0 and COM can also increase lifetime.  

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Ynvisible E-Paper Driving Schemes 

Below are a few different driving schemes suggestions. We also indicate which circuit suggestions described above are compatible with the driving schemes. 

Definition of the conventions used in the following driving schemes:  

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                                                                                  Before Update               After Update

Driving Scheme A (Compatible with circuits 1, 2 & 3) 

This driving scheme updates the display in two steps. First, some segments are turned OFF by setting the common electrode to 1,5V and the relevant segment electrodes to LOW/0V (resulting in -1,5V across the segments). Secondly, some segments are turned ON by setting the common voltage to VSUPPLY-1,5 and the relevant segment electrodes to HIGH/VSUPPLY (resulting in +1,5V across the segments). A shorter refresh pulse is required on the segments that should be kept in ON state. The sequence ends with setting all signals to High-Z to maintain the state.

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Driving Scheme B (Compatible with circuits 1, 2, 3 & 4) 

This driving scheme updates the display in two steps, like driving scheme A, but without a variable common electrode voltage. First, some segments are turned OFF by setting the common electrode to HIGH and the relevant segment electrodes to LOW/0V (resulting in - VSUPPLY  across the segments). Secondly, some segments are turned ON by setting the common voltage to LOW and the relevant segment electrodes to HIGH (resulting in +VSUPPLY across the segments). A shorter refresh pulse is required on the segments that should be kept in ON state. The sequence ends with setting all signals to High-Z to maintain the state. If the system operates at a low voltage or if lifetime requirements are limited, this could be a good option.

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Driving Scheme C (Compatible with circuits 1, 2 & 3 if |VON| + |VOFF| = Vsupply) 

This driving scheme updates the display in one single step. The segments are turned ON and OFF at the same time. This is enabled by setting the common electrode to a voltage in between LOW and HIGH, typically ±1,5V for a 3V system, but could also be, for example, ±1V for a 2V system. In this way, a positive and a negative voltage can be applied to the respective segment simultaneously. A shorter refresh pulse is required on the segments that should be kept in ON state. The sequence ends with setting all signals to High-Z to maintain the state.

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Driving Scheme D (Compatible with circuit 4) 

This driving scheme updates the display in one step, like driving scheme C. The display is enabled by applying a PWM signal to the common electrode to simulate a virtual ground between the LOW and HIGH. On many MCUs, this driving approach causes significant leakage leading to significantly higher energy consumption than driving scheme C. The sequence ends with setting all signals to High-Z to maintain the state.

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Driving Scheme E (Compatible with circuit 4) 

This driving scheme updates the display in one single step like driving scheme C, but with the difference that the turn-off voltage is 0V. Turning off the segments with 0V is significantly slower than applying a negative voltage (for example -1,5V). For this reason, it takes a longer time for the segment that should be turned OFF to switch, compared with the segments that should be turned ON. A shorter refresh pulse is required on the segments that should be kept in ON state.  The sequence ends with setting all signals to High-Z to maintain the state. This driving method can connect the common electrode directly to the ground.

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Conclusions 

Integrating and driving Ynvisible’s e-paper displays are relatively straightforward compared to other display technologies. To get started right away, visit the Ynvisible Store to see our available hardware. Do not hesitate to contact sales@ynvisible.com if there are any questions.

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