I have a 20x4 alpha numeric symbol but it is connected to an I2c serial adaptor, I can’t find one of those. Does anyone know if one exists and where to find it?
I’m not exactly sure what you’re looking for, but it seems like some special / unusual combination. There simply are no standardized I2C connectors.
When I look at your profile:
I see you’re on this forum for over 5 years, and I recon it’s high time to start using the symbol and footprint editors to make your own symbols and footprints. In fact, the quality of the symbol and footprint editors it one of the reasons I started using KiCad (over 10 years ago) in the first place.
Hi paul, I suppose you have a point, I didn’t want to duplicate something that already exists. What I am looking for is the adaptor I have on the back of most of my 20x4 and 16x2 displays, this one
Ah, one of those things.
Connectors don’t go further then the standard basic connector, so single row headers in this case.
I’ve seen those boards (I see PCF8574) and I find it quite sad these things have become so common. I never used them myself. My own solution would be to use a small uC (which is probably cheaper then such an I2C expander chip also) and use it as the interface between I2C and the HD44780 (compatible) LCD. I find the Idea of bit banging the HD44780 over I2C in this way a bit atrocious. I would much rather devise a simple command protocol, and then just send text strings over I2C. With such an expander, you have to end a lot of I2C packets, just to send one character to the LCD. With a text string, there is both much less I2C traffic, and much less overhead for the sending uC.
Hmm, I don’t quite understand your dislike of them, I usually get them off old units soldered to the displays that I dismember (and often I mean dismember) and there are so many good libraries for the use of them with just 2 pins (+vcc and 0v).
I thought my explanation was quite clear. But it’s your project, and it’s also a bit off topic.
Those are standard Dupont pins on 0.1" pitch on the adaptor which uses a standard I2C to parallel expander chip which then drives the HD44780. They would normally be connected with a 4 conductor cable. Just draw a symbol box with 4 pins, 2 power, 2 I2C bus.
1 Like
Hey Paul – there are two de-facto standards:
Seeed’s “Grove” (JST-PH 2mm 4pin) (elecrow calls it “Crow” but I believe Seeed defined it).
Sparkfun “Qwiic” (JST-SH 1mm 4pin) – Adafruit endorses (possibly co-developed, not sure).
Both of these are really handy standards – I use one on most every board I do.
It’s nice since the connectors are easy and cheap to get, and there are a variety of lengths of pre-crimped cables available for both. Sadly, neither of them interleaved power/gnd with signals to keep crosstalk down, but i2c is pretty low-freq.
Yeah, this does not address the OP question, but fyi.
The great thing about ‘standards’ is there’s usually more than one. . . :rolleyes:
That’s a classic XKCD 927:
I sort of like the UEXT connector from Olimex. It’s got I2C, SPI, UART and Power on a single 10 pin IDC connector. And there are more “of course”…
Grove connectors are usually called a “HY-2.0”, and are (incorrectly) commonly associated with JST, but were developed in China. They’re similar to a PH but with locking prongs on the plug.
This old Reddit post includes some sourcing details: https://www.reddit.com/r/AskElectronics/comments/jgo5hq/mysterious_hy20_connectors/?rdt=65428
Edit: A comparison between the connector types - Stemma, Qwiic and Grove Connectors: Which is Right for You? | Tom's Hardware
Here is a project where we integrated a 20x4 LCD on a PCB with the I2C expander on the PCB
Schematic and PCB here.
CAUTION. this Rev 1 PCB had an error on the USB to UART part. Missing the 12MHz cyrstial so do not build this version PCB.
