In this example we are going to connect to some specialized HD44780 based displays.
This article is followup on our previous article called HD44780 based LCD display.
The standard 16 x 2, or 20 x 2 or even 20 x 4 are great for many purposes, and cheap as well.
But sometimes you just want different size, different character count or even different panel color. For those reasons we wanted to test some of the less standard mainstream HD44780 displays. Note that when dealing with rare sizes then you cannot shop around for as low prices as with the standard sizes.
Displays that we will be looking at:
- 40 x 2 – ERM4002-1 Series display from buydisplay.com.
- 40 x 4 – ERM4004-1 Series display from buydisplay.com. (This one has two channels and needed special attention).
- 8 x 2 – ERM802-3 Series display from buydisplay.com.
40 x 2 display – ERM4004-1 Series (Blue background):
Just like with most of the standard size displays then I had to solder header pins on all the displays.
I got this one to work with the same code as the standard 16 x 2 from the original article, and was able to use 40 letters per line as well as the custom glyph feature.
The header pin arrangement was a bit different from the standard 16 x 2 display, but pin numbers are compatible. Instead of one line of pins then we have 2 columns arranged as follows:
The header pins on the 40 x 2 display.
Connection map (same as in the original article):
| LCD | Raspberry PI cobbler |
|---|---|
| #1 (GND) or (VSS) | GND |
| #2 (VCC) | 5v |
| #3 (Vo) | To potentiometer middle pin |
| #4 (RS) | GPIO25 |
| #5 (RW) | GND |
| #6 (EN) | GPIO24 |
| #7, #8, #9, #10 | not used |
| #11 (D4) | GPIO23 |
| #12 (D5) | GPIO17 |
| #13 (D6) | GPIO21 |
| #14 (D7) | GPIO22 |
| #15 (LED+) | to 560 Ω resistor that then goes to 5.0v |
| #16 (LED-) | GND |
See the original article for more detail on how to connect the potentiometer and how it all comes together.
40 x 4 display – ERM4004-1 Series (White background):
The 40 x 4 is very large, the picture bellow does not give good idea of the size, but it is much longer than iPhone 7 plus for example.
With this one things got a bit tricky, it does not have pin compatibility with the original article for the 16 x 2 display, and this display comes with 2 enable pins which is due to the fact that it has basically 2 controllers. Because of this then updated Xojo code was needed so that it could support displays that need two controllers.
Updated Xojo code can be downloaded bellow. (And of course we made sure that the custom glyphs work for both the controllers in the display).
The 40 x 4 comes with two headers, one on right side and one on left. Where the header for the backlight has been separated from the main header.
The header pins on the 40 x 4 display.
Connection map (Note note same as in the original article and this one has two E pins):
| LCD | Raspberry PI cobbler |
|---|---|
| #1 (D7) | GPIO22 |
| #2 (D6) | GPIO21 |
| #3 (D5) | GPIO17 |
| #4 (D4) | GPIO23 |
| #5, #6, #7, #8 | not used |
| #9 (E1) | GPIO24 |
| #10 (RW) | GND |
| #11 (RS) | GPIO25 |
| #12 (VEE) | To potentiometer middle pin |
| #13 (VSS) | GND |
| #14 (VCC) | 5v |
| #15 (E2) | GPIO13 |
| #16 | not used |
| #17 (LED+) | to 560 Ω resistor that then goes to 5.0v |
| #18 (LED-) | GND |
Downloading the updated code to support dual channel displays that have two enable pins:
8 x 2 display – ERM802-3 Series (Blue background):
The pin layout of the 8×2 was a bit strange, notice where pin 15 and 16 are vs 1 and 2. But apart from the strange layout then the 8×2 connects in mostly same way as the 16×2 in our original guide (except pins 15 and 16).
The header pins on the 8 x 2 display.
Connection map (mostly same as in the original article except pin 15 and 16 are swapped):
| LCD | Raspberry PI cobbler |
|---|---|
| #1 (GND) or (VSS) | GND |
| #2 (VCC) | 5v |
| #3 (Vo) | To potentiometer middle pin |
| #4 (RS) | GPIO25 |
| #5 (RW) | GND |
| #6 (EN) | GPIO24 |
| #7, #8, #9, #10 | not used |
| #11 (D4) | GPIO23 |
| #12 (D5) | GPIO17 |
| #13 (D6) | GPIO21 |
| #14 (D7) | GPIO22 |
| #15 (LED-) | GND |
| #16 (LED+) | to 560 Ω resistor that then goes to 5.0v |
I had 20 x 2 and 24 x 2 ready but I decided to not solder them and cover them for now as their interface and specs hinted that they were just like the 40 x 2, so not offering any new knowledge.
Then there was a miniature 12 x 2, which had normal header except backlight cathode pin is missing, I assume the ground is just shared with other ground pins. But I could not solder that one as it needed 2x narrower header pins which I did not have.