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Colour GLCD for calculator project
05-16-2019, 05:23 AM (This post was last modified: 05-16-2019 05:32 AM by Dan.)
Post: #1
Colour GLCD for calculator project
Wondering if anyone has experience interfacing one of the many higher resolution colour GLCD's now available? I am looking at replacing the black and white 128x64 GLCD I've been using with a colour one. An electronics magazine I bought the other day had an article on interfacing this 3.5 inch GLCD to an Arduino.

It is a 480x320 colour GLCD with an SD card holder and uses SPI to communicate with the microcontroller. My main concern is that the relatively high resolution could result in a slow refresh rate, especially as it uses SPI. Here is a 4 inch 480x320 colour GLCD with an 8-bit parallel interface, which is faster but uses more microcontroller pins.
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05-16-2019, 08:56 AM
Post: #2
RE: Colour GLCD for calculator project
Just curious... What is a GLCD and why is it different from an LCD?
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05-16-2019, 10:35 AM (This post was last modified: 05-16-2019 10:39 AM by Maximilian Hohmann.)
Post: #3
RE: Colour GLCD for calculator project
Hello!

(05-16-2019 08:56 AM)grsbanks Wrote:  Just curious... What is a GLCD and why is it different from an LCD?

I would interpret the "G" as the initial letter of "Graphic".

Regarding the original question: The higher resolution graphics capable LCDs that I have played with so far all came with an Arduino "shield" for the connections. Two monochrome ones are installed in my 3D printers and I got another 2 or three colour ones for future experimenting. The ones I have tried so far all come with 8 bit parallel buses and require 11 or 12 lines in total.

However recently I acquired two "smart" LCD displays (with the intention of eventually using them for an Apollo guidance computer DSKY replica) from Nextion (https://nextion.itead.cc/). These are pretty amazing devices which come with their own microcontollers and on-board "intelligence" and require only minimal amounts of data transfer from their host computer. I guess it should be even possible to program them as a standalone four-function calculator with touch interface. On the internet I have seen stuff like standalone Tic-tac-toe.
These displays require a PC application for configulation and programming. The program can then be transferred either by a serial connection or (very easy!) via SD card. Once it is programmed, 2 way serial communication from the Arduino requires only two lines. The main disadvatage may be their price: the smallest 2.4in Nextion display costs around 15 $/Euros including shipping compared to a similar sized "dumb" TFT shield that comes for less than 3 $/Euros). The other disadvantge is the display itself which is not as good as those we know from our modern smartphones. Especially the viewing angle is somewhat limited.

I took some photos for comparison of some displays I pulled out of one of my tinkering boxes. The first one is for size comparison shows an overview of 3 Arduino boards (Nano, Mega and Uno) and 3 grahic displays:
A 2.8in dumb TFT Shield, a 3.5in Nextion and a 5in Nextion.

[Image: IMG13534_1024px.jpg]

This is the backside of the dumb display shield . It shows how many lines are connected to the Arduino. It uses more connections than necessary for the display itself because it gives touch feedback as well and there is also an SD card interface and a temperature sensor. There are plenty of libraries online for these boards and lots of examples.

[Image: IMG13535_1024px.jpg]

The next two pictures show the backsides of the 3.5 and 5 inch Nextion displays. The amount of components shows why they are more expensive. But the relative ease of programming and the minimal number of connections required compensates for the difference in price.

Regards
Max

[Image: IMG13536_1024px.jpg]

[Image: IMG13537_1024px.jpg]
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05-16-2019, 01:57 PM
Post: #4
RE: Colour GLCD for calculator project
I got this working pretty easily with an LPC1114: https://www.adafruit.com/product/358

This one for $2.50 is probably the same thing if you want to take the risk: 1.8 LCD on Aliexpress
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05-16-2019, 02:08 PM
Post: #5
RE: Colour GLCD for calculator project
one of my projects is to see if I can duplicate the 48sx some day. I've been playing with the source for x48 and compiling on a couple mcu's like the PIC and AVR (arduino) then plan to make a keyboard and lcd like these and eventually have a whole calculator.
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05-17-2019, 02:21 AM
Post: #6
RE: Colour GLCD for calculator project
(05-16-2019 01:57 PM)Druzyek Wrote:  I got this working pretty easily with an LPC1114: https://www.adafruit.com/product/358

This one for $2.50 is probably the same thing if you want to take the risk: 1.8 LCD on Aliexpress

Yes you never can be sure about the cheaper ones. The Adafruit display is nice, but a bit too small. I'll see if there is a larger display with the same ST7735R driver, say around 3.5 to 4.5 inches. From experience getting these things to work can be a challenge, the more example interface software available the better.
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05-17-2019, 02:26 AM
Post: #7
RE: Colour GLCD for calculator project
(05-16-2019 08:56 AM)grsbanks Wrote:  Just curious... What is a GLCD and why is it different from an LCD?

The graphical (G) displays enable you to turn individual pixels on and off, whereas LCD's can only display characters, e.g. four function calculators, fax machines etc.
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05-17-2019, 03:11 AM (This post was last modified: 05-17-2019 03:53 AM by Dan.)
Post: #8
RE: Colour GLCD for calculator project
(05-16-2019 10:35 AM)Maximilian Hohmann Wrote:  This is the backside of the dumb display shield . It shows how many lines are connected to the Arduino. It uses more connections than necessary for the display itself because it gives touch feedback as well and there is also an SD card interface and a temperature sensor. There are plenty of libraries online for these boards and lots of examples.

[Image: IMG13535_1024px.jpg]

Thanks for the detailed response Max, much appreciated. The Nextion displays look nice but I don't know if they will work with my 3.3V logic microcontroller. So I am leaning towards something like the 2.8 inch display above, but larger, around 3.5 inches. I like the parallel interface and the SD card interface. And the ready availability of interface software is a must for me - these things can be a real pain to get working otherwise.

However I'm not sure if this particular 2.8 inch display will work with my 3.3V logic microcontroller. A lot of these displays are designed for the Arduino/RPi and feature additional circuitry to convert 5V to 3.3V, perhaps the shield is expecting 5V from the pins?

Also, how do you find the performance of the higher resolution displays in general? Does it take a noticeable amount of time to refresh the screen? You certainly don't want the user waiting for the value entered on the command line to appear on the stack!

Once I find a display, Dirk Heisswolf, creator of the AriCalculator hardware, has kindly agreed to start designing PCB's to turn my TI LaunchPad prototype into a handheld unit, which is pretty exciting. The idea is to plug one PCB with the keys and display attached to it into the male header pins on top of the LaunchPad, and the other PCB for the power supply into the female pins underneath the LaunchPad.

So if anyone knows of a quality 3.3V GLCD around 3.5 inches with parallel interface and SD card connection, please let me know!

EDIT: Even without TFT, parallel + SD card uses a lot of pins, judging from the underside of the 2.8 inch. The TI LaunchPad has 40 pins but 14 are used for the 8 row, 6 column matrix keypad. Perhaps SPI is better - it really depends on how long it will take to redraw the higher resolution display. I am about to upgrade to the TM4C1294XL, which is 120MHz, so hopefully that will give acceptable results.
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05-17-2019, 10:03 AM (This post was last modified: 05-17-2019 10:11 AM by Maximilian Hohmann.)
Post: #9
RE: Colour GLCD for calculator project
Hi!

(05-17-2019 03:11 AM)Dan Wrote:  Also, how do you find the performance of the higher resolution displays in general? Does it take a noticeable amount of time to refresh the screen? You certainly don't want the user waiting for the value entered on the command line to appear on the stack!

I don't think that's a problem. Of course these are not the state of the art daylight-readable instantaneous retina displays that Apple uses for their iPhones. But in my experience this kind of display is quicker than something like the original HP-48.

(05-17-2019 03:11 AM)Dan Wrote:  So if anyone knows of a quality 3.3V GLCD around 3.5 inches with parallel interface and SD card connection, please let me know!

Lady Ada has one matching your specs (even with a choice of parallel or serial connection) but only 3.2 inches: https://learn.adafruit.com/adafruit-2-do...2/overview
The good thing with Adafruit products is that their drivers and libraries are always up to date and match the hardware. With the cheap clones from China it can take some time to find a working library and to adjust all the necessary settings.

Regards
Max

Edit: There is also a 3.5in version of these displays, it is just not covered by the tutorial I linked above but should be just the same: https://www.adafruit.com/product/2050
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05-17-2019, 10:07 AM
Post: #10
RE: Colour GLCD for calculator project
(05-17-2019 02:26 AM)Dan Wrote:  The graphical (G) displays enable you to turn individual pixels on and off, whereas LCD's can only display characters, e.g. four function calculators, fax machines etc.

Interesting. I never knew that the definition of LCD (Liquid Crystal Display) precluded pixel-by-pixel addressability. The thousands of manufacturers who call them simply "LCD" must all be wrong.
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05-17-2019, 12:00 PM
Post: #11
RE: Colour GLCD for calculator project
(05-17-2019 10:07 AM)grsbanks Wrote:  
(05-17-2019 02:26 AM)Dan Wrote:  The graphical (G) displays enable you to turn individual pixels on and off, whereas LCD's can only display characters, e.g. four function calculators, fax machines etc.

Interesting. I never knew that the definition of LCD (Liquid Crystal Display) precluded pixel-by-pixel addressability. The thousands of manufacturers who call them simply "LCD" must all be wrong.

It's probably just nomenclature used in the embedded dev systems market to differentiate LCDs strapped to a character generator and controlled via a simple serial interface from the ones that are directly addressable.
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05-17-2019, 11:13 PM
Post: #12
RE: Colour GLCD for calculator project
(05-16-2019 05:23 AM)Dan Wrote:  and uses SPI to communicate with the microcontroller. My main concern is that the relatively high resolution could result in a slow refresh rate, especially as it uses SPI.

How fast is it? I didn't see anything at the link that tells. SPI has no max speed limit; and there are some SPI devices that approach 100MHz clock rates, 100 Mbits per second, ie, about 12 Mbytes per second.

http://WilsonMinesCo.com (Lots of HP-41 links at the bottom of the links page, http://wilsonminesco.com/links.html )
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05-18-2019, 10:42 AM
Post: #13
RE: Colour GLCD for calculator project
(05-17-2019 11:13 PM)Garth Wilson Wrote:  
(05-16-2019 05:23 AM)Dan Wrote:  and uses SPI to communicate with the microcontroller. My main concern is that the relatively high resolution could result in a slow refresh rate, especially as it uses SPI.

How fast is it? I didn't see anything at the link that tells. SPI has no max speed limit; and there are some SPI devices that approach 100MHz clock rates, 100 Mbits per second, ie, about 12 Mbytes per second.

True, SPI is fast, but I think the parallel interface is faster.
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05-18-2019, 10:43 AM
Post: #14
RE: Colour GLCD for calculator project
(05-17-2019 10:03 AM)Maximilian Hohmann Wrote:  Hi!

Lady Ada has one matching your specs (even with a choice of parallel or serial connection) but only 3.2 inches: https://learn.adafruit.com/adafruit-2-do...2/overview
The good thing with Adafruit products is that their drivers and libraries are always up to date and match the hardware. With the cheap clones from China it can take some time to find a working library and to adjust all the necessary settings.

Regards
Max

Edit: There is also a 3.5in version of these displays, it is just not covered by the tutorial I linked above but should be just the same: https://www.adafruit.com/product/2050

That's perfect, thanks Max. I think I'll order the 3.5in.
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05-18-2019, 10:46 AM
Post: #15
RE: Colour GLCD for calculator project
(05-17-2019 12:00 PM)Dave Britten Wrote:  
(05-17-2019 10:07 AM)grsbanks Wrote:  Interesting. I never knew that the definition of LCD (Liquid Crystal Display) precluded pixel-by-pixel addressability. The thousands of manufacturers who call them simply "LCD" must all be wrong.

It's probably just nomenclature used in the embedded dev systems market to differentiate LCDs strapped to a character generator and controlled via a simple serial interface from the ones that are directly addressable.

That's right, I should have said graphical (or individual pixel control) LCD and character LCD. They are both LCD's, of course.
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