Low cost character display solution

[josuah]

When looking for a simple way to display a menu for i.e. tweaking voltage, temperature, brightness... anything, plain LEDs do not cut it, and graphical screen can be an overkill and higher price.

It is possible to find inexpensive screens from some suppliers:
https://www.buydisplay.com/graphic-display/graphic-display-panel
https://www.buydisplay.com/oled-display

Graphic displays (LCD or OLED):

(+) Very flexible for displaying complex graphics.
(-) More RAM needed for storing the font.
(-) More work to write drivers for them.
(-) The price quickly goes up with size.
(+) Font chips circumvent that, sometimes built into the display.
(+) Not so many different driver to write.

LED segment displays:

(+) Very low price at any size.
(+) Chips like TM1650 means only 2 MCU pins to drive many character cells.
(+) Quite robust and easy to repair
(-) A bit more PCB work
(-) Not many characters to display

Segment LCD display:

(+) Good daylight visibility (useful for outdoor)
(+) Optional backlight
(+) Very low power
(+) Low price
(-) Often require dedicated hardware and many pins to drive, or an ASIC

Bubble Segment Displays:

(+) same advanages as LED segment displays
(+) Smaller size
(+) Lower price?
(+) Smaller power?
(-) nowhere to be found!

=> What happened to the bubble segment displays? Why replaced by the modern alternatives?
=> What is your approach for when you need a few alphanumerics but 128x32 pixels are an overkill?

[Kleinstein]

The bubble LED displays where mainly a thing before the larger ones got practical with better LED efficiency.

The list is missing one important option: the character based LCD modules. So a small graphics LCD with controller to write charcters for something 1-4 line with 8 -32 charactes. They can be realtively cheap, though some are also in the $10-20 range.

[Ian.M]

What about character LCD modules with on-board HD44780 compatible controllers?   Readily available in various sizes from 8x1 single line displays to 40x2 or 20x4 multiline displays.  The only significant disadvantages  are the retro look, the limited character set (usually Latin + Japanese katakana with a few Greek letters, and eight UDGs),  and the parallel interface with even write-only 4 bit mode requiring six MCU I/O pins.

Edit: Kleinstein beat me to the character LCDs

[josuah]

Just for fun, some links to projects made out of these old bubbledisplays:

https://hackaday.com/2019/12/10/chaining-together-a-16x2-bubble-led-display/
https://hackaday.com/2022/01/11/led-bubbles-from-the-1970s-tell-the-time/
https://hackaday.com/2014/06/20/the-ultimate-tiny-altimeter/

[josuah]

The parallel interface with even write-only 4 bit mode requiring six MCU I/O pins.

This might be turned down a bit more with an inexpensive shift register, but a serial character LCD panels make sense.

The bubble LED displays where mainly a thing before the larger ones got practical with better LED efficiency.

So small segment LED displays were withdrawn as soon as larger segment LED displays came... Interesting.

The list is missing one important option: the character based LCD modules. So a small graphics LCD with controller to write charcters for something 1-4 line with 8 -32 charactes. They can be realtively cheap, though some are also in the $10-20 range.

A bit bulky and more expansive than some graphical counterparts.
I'll need to search better.
Nontheless, they definitely fill the gap between fully-graphical displays and character displays.

[MikeK]

If the 128x32 OLED is overkill for you, there are even smaller ones such as 0.42" 72x40, 0.49" 64x32, and I've heard there is a 0.28" unit but I haven't seen it.

[josuah]

Interesting thing: hybrid solutions such as https://radiant-display.com/products/rc1602-79-16x2-character-lcd-chip-on-glass

If the 128x32 OLED is overkill for you, there are even smaller ones such as 0.42" 72x40, 0.49" 64x32, and I've heard there is a 0.28" unit but I haven't seen it.

Definitely interesting things to lookup indeed.

[themadhippy]

and the parallel interface with even write-only 4 bit mode requiring six MCU I/O pins

If the mcu has i2c convertors can cut that down to 2 pins

[mariush]

There's displays which don't separate the pixels into lines of text, but use same hd44780 compatible controllers  or something with a similar protocol... you can "upload" your own bitmap font or use the one built in the chips and print characters wherever you want

Example :

122x32 pixel  with controller that uses hd44780 like commands : https://newhavendisplay.com/122x32-graphic-lcd-module-stn-yellow-green-display-with-yellow-green-backlight-with-voltage-converter/

128x64 pixel with controller that does serial or parallel (link example exposes only serial) : https://newhavendisplay.com/128x64-graphic-cog-lcd-fstn-display-with-white-side-backlight-and-built-in-heater/

240x128 pixel , another controller with similar command set to hd44780 : https://newhavendisplay.com/240x128-graphic-lcd-module-fstn-display-with-white-backlight/


There's also VFD displays besides lcd and oled ... expensive : https://newhavendisplay.com/vfd-displays/dot-matrix-displays/

and I'm sure you can find small eInk displays on aliexpress/alibaba or somewhere (but for some of these, you may also need weird voltages like +15v so that's extra voltage doublers /step-up regulators on board)

for example 2.9" 298x128 eInk  (7$ for 1, 4$ for 10k+) : https://www.alibaba.com/product-detail/2-9-Inch-296-128-E_1600486623944.html

[MikeK]

Definitely interesting things to lookup indeed.

I like those 8x2 LCD's...I have a bunch of them.  I wish they were as inexpensive as the SSD1306 OLED's, though.

[josuah]

It looks like someone had fun trying to do some very small digit display:
https://hackaday.com/2022/11/30/nano-sized-7-segment-led-display-on-a-surface-mount-module/

[josuah]

In the same series of these retired products, the PDSP1881 / PDSP1884:

These are much like the character displays, but without an integrated chip (might require a driver or at least chip register chip), and still sold in "end-of-life" pricing (about 10 cent per 8-char module):
https://octopart.com/search?q=PDSP&currency=USD&specs=0&category_id=4408



https://www.industrialalchemy.org/storearticleview.php?item=96

[josuah]

Given segment displays are a single component, it could be interesting to have some with a built-in shift register:

Code: [Select]

             .-------.
SERIAL_OUT---|  --   |---SERIAL_IN
SERIAL_CLK---| |  |  |---SERIAL_CLK
             |  --   |
       VCC---| |  |  |---VCC
       GND---|  -- o |---GND
             '-------'

The cost would be a bit higher, but it would save a lot of MCU pins, or eventually save the need for a HT16K33-style chip.

Plug the serial out of one chip to the serial in of the next, and feed the display with whatever value you wish, then turn the MCU off, with wake-up on interrupt from buttons:

Code: [Select]


                  .-------.   .-------.   .-------.   .-------.
 x---SERIAL_OUT---|  --   |---|  --   |---|  --   |---|  --   |---SERIAL_IN----.
 x---SERIAL_CLK---| |  |  |---| |  |  |---| |  |  |---| |  |  |---SERIAL_CLK--.|
                  |  --   |   |  --   |   |  --   |   |  --   |               ||
            VCC---| |  |  |---| |  |  |---| |  |  |---| |  |  |---VCC         ||
            GND---|  -- o |---|  -- o |---|  -- o |---|  -- o |---GND         ||
                  '-------'   '-------'   '-------'   '-------'               ||
                                                                         MCU--'|
                                                                         MCU---'

The input is at the right of the display to enable a scroll effect by feeding only 8 bits (1 byte) at a time.