Control circuitry of polymer based display

[Hassaankhi]

Hi folks!

I am working on some polymer (PEDOTSS) based display. Some basic physics about this display in order to understand what I would like to know.
Such displays operate at 2.5-3 V. They change color from white to blue (reduction state) and blue to white (oxidation state) upon supplying voltages. These displays retain their state (blue or white) for certain period of time even the voltages are removed so they show memory effect more like a capacitor.
I have two types of such display: 1. 7-segment and 2. Matrix of 8x8.

I want to develop separately driver circuitry for both displays means a separate drive for 7-segment and a separate driver for matrix display. I know enough about the operations of these display

I want to ask that from which point I should start with? I have googled for driver and I found lot of block diagrams of drivers for example 7-segment (LED) displays which consists of decoder, multiplexer etc. Can anybody provide me some starting help designing of this driver?
I am very thankful to you.
Thanks for your time to read my problem.

Hassaan

 

[alec_t]

Can you post a link to the datasheets for those displays?

 

[Hassaankhi]

alec_t
Thanks for your reply and reading my problem.
I am afraid there is no such datasheets like conventional 7-segment and matrix display have. But I can explain the display.
For every segment there are two electrodes; 1. counter electrode and 2. pixel electrode. If you want to have blue color (reduction state) you need to supply 2.5-3 V to counter electrode and 0 V to pixel electrode. And for white color you need to reverse. If we have a 7-segment display so every segment has one seperate counter electrode but pixel electrode is common to all 7 segments. Display behaves as a parallel plate capacitor.

 

[Hassaankhi]

one clarification: I wrote PEDOT PSS separated with semi colon : but there appeared a cheeky emoticon. Material is PEDOT semicolon PSS

 

[alec_t]

I have no experience at all with that sort of technology, but my approach would be to bias the pixel (common) electrode at 2.5V and use conventional 5V logic circuits to switch the counter electrodes individually to either 0V or 5V as required.
How much charge is required to switch the display element state?
How critical is the 2.5-3V rating?
What maximum current can the elements draw when the capacitance is charging/discharging?

 

[Hassaankhi]

Thanks for your reply.
The voltage rating is quite critical for the life time of the display. If the voltages are exceeded let say 3.5 V during white state, a greater chance to destroy the display. This process of changing color is reversible process which quite dependent on the applied potentials and time. Display will be destroyed either higher voltages are applied or if nominal voltages are applied for extended period of time.
The current rating is in micro amps range. For example to turn the display into blue state from white state, it draws current around 15 uA and become constant around few nano amps.

 

[ronsimpson]

25 to 30 years ago this question was asked to me. (LCD)
and about every 10 years I get this question.

Just to make sure: There is a (-) and a (+) mode and a memory mode.
(-) and (+) need 2.5 to 3 V. That is easy.
Does each pixel or segment require a different voltage or can we set the entire display to the same voltage?
Does the (+) and (-) have the same value? (+2.7 and -2.7)
How long will the memory last. 10mS??
What is the voltage in memory mode? Must the wires be "open" or can we apply (0) volts?

What equipment do you have?
>bench power supply?
>How are you going to generate data for the display?
>>PC to display, Micro0computer to display, switches to display???

 

[Hassaankhi]

Hi ronsimpson

I am really glad to see the reply.
I guess there would be a law in future from you like Moore's Law for such display question.

We can drive the display with two polarities (-) for reduction state i.e. for blue color and (+) supply for oxidation i.e. for white color. But both operation can be achieved with single supply. Since there are two electrodes 1. Counter electrode and 2. Pixel electrode which is common to all segments. To get blue color we need to give 3V to counter electrode and 0V to pixel electrode. While for white color (oxidation state) it is reverse i.e. 3V to pixel electrode and 0V to counter electrode.
The switching time for both states varies with amount of voltages. Which means we can change the state with lower voltages for example 2V or less but the response time will be quite slow and fill factor will be very less. So 3V are chosen as best. Switching time with 3V supply is around 200 msec.
The memory effect lasts for ~15-20 minutes.
The voltages across each segment in memory mode (when the power is removed) around 1.3-1.5 V during blue color while around 2V during white color.
After supplying the blue or white color voltages we need to put the electrodes in High-Z (high impedance mode) otherwise either ground or some voltages will affect the color.
I have an arduino UNO board with which I played around. But since I have no background in electronics having problems in designing a proper driver circuit for such displays.
I do not know how I will generate the data, may be read from some memory and then store to some buffer and then apply to the corresponding electrodes. But I wrote some small programs which display numerals e.g 0-9. The 7-segment display can be thought as a matrix of 1 row (pixel electrode) and 7 columns (counter electrodes), I guess.
Can you provide me some rough idea in form of block diagram? Highly appreciable.
I have attached a picture of 7-segment display.

Thanks for reading the problem.
Hassaan

 

[Hassaankhi]

There is a demonstration of such display here:
**broken link removed**

 

[ronsimpson]

So you have an arduino UNO, good!
We will use it. I hope you can get 5V from it or a bench supply.
Connect D0,1,2,3,7 and ground.
Here is a drawing. The pot sets a voltage from 0 to 5 volts.
IC2 has three switches inside. 74hc4043. (5 volt version) The switch is spdt. Input A causes the switch to connect to X0 or X1.
Two of the switches are connected to D7 switches both of them. Pin 14 and 15 will be (+)/(-) or (-)/(+) depending on D7.
IC1 is a 1 or 8 switch. 74hc4051 Inputs ABC select which position the switch is in. INH needs to be low for the switch to work.
D0,1,2,3 will select which segment is connected. (one at a time)

Set the pot for 2.5 volts.
Set D7 for blue or white. Now set D0-D4 to segment A or D0,1,2,3 = 0,0,0,0. Segment will have a +/- voltage.
You will need to select each segment A....G while you set D7 for white or Blue.
At the end you can take INH=1 to stop setting segments.
You will probably need to keep updating the display every 10 seconds. ????