Updated August 07. 2016: This article which started off discussing the “new addition” of i2c to the home control software, is now NOT ONLY about an I2c  2/4 line LCD display facility recently added to the ESP8266 boards – but there’s a PARALLEL version as well, making use of GPIO 4,5,12,13,15 and 16. And NOW – I’m adding a pretty crude interface for the Seeeed OLED displays with other OLEDs to follow.

Comments below about format apply equally to the I2c and parallel versions – for the latter, simply use device 255. Note when you do that you lose GPIO13 as an indicator automatically until next power-up.

Success with I2c – once I realised there was something up at the Arduino end which I could work around, my ESP8266 I2c endeavours have been coming on in leaps and bounds!

And here is my test rig – or one of them – I have one for I2c display and another for parallel display  - the latter is just as messy and has more wires:

So what you’re looking at there from top to bottom – is a prototyping ESP8266 board (the author will recognise it) just because I had it handy – ESP-12 based, running my rapidly developing software (which now has loads of spare RAM thanks to the SDK 2.0). I put a simple set of i2c commands in there then promptly realised that a series of commands sent by MQTT would not be a lot of use. I then proceeded to waste the day, having already talked successfully to an 8-bit port expander, trying to get one of those back-of-an-LCD I2C boards to work – as it was based on the same chip.

After several hours of considering taking up brick-laying I realised the damned thing was bust – and went off in search of my  cheap Chinese port expander – that’s the red thing you see in the middle. The only difference is this does not have a transistor to power an LCD backlight so I just hardwired that. At the bottom – the original test 4-line LCD. Over on the right, an irrelevant Arduino-type board which is also talking I2c successfully.

Having decided I liked the idea of plugging one of the cheap LCDs onto the odd home control board for information purposes, I set about doing something I’ve never done before – reading the Hitachi data sheet. These things are quite cute once you get over starting in 8-bit mode then switching to 4-bit to save on wires etc… (so in total you only need 6 signals to talk to the LCD) and after some timing experimenting (clear screen command takes a while – over 1.5ms) as you can see I finally have a working LCD – and by the look of it, rock-solid reliable.

So what is driving that display (which is updating every second virtually instantly)…

This:

and inside that inject?

Topic: freddy/toesp

Payload: {hitachi:39,"$1MQTT test$2$i$3Time $t$4Date $d"}

For clarification - that is a string - which starts and ends with "{" - it is not JASON or ann object. So if you want to send this from, say a Node-Red function you'll have to consider escaping strings.

You might wrap the whole thing in single quotes for example.

That’s all. So assuming you’re familiar with MQTT (if not – look at other articled in here) the destination is the little board “freddy” – and the new command I’ve just added – “hitachi” talks to an i2c board (the expander) device #39 and sends out that string.

Rather than have a boatload of commands which would be unwieldy in the home control setup – or special characters which might cause issues – I used the dollar as an escape character. Here’s what I’ve implemented up to now

1. $$ -  well that shows a dollar on the screen !!
2. $s -  setup – sets up a virgin LCD and clears the screen
3. $c  - clear the screen
4. $1 – set the cursor to line 1 -  ($2 $3 $4)
5. $t  -  fire out the time
6. $d – fire out the date
7. $i  -  fire out the current ip address

I’ll probably settle on a 2-liner as they are sub-£2 from China – indeed for 20-off just over £1 – and at £1.34 for the port expander – around £3 to add a nice little display to some of the ESP8266 boards – can’t be bad. indeed, using one of the port expanders for an ultra-low-cost i2c keypad isn’t a bad idea. 45p for the keyboard, £1.34 for the expander… Sub-£2 keypad.

Clearly one way to wipe a line would be “$1               $1” which is probably fast enough for most purposes. I’ll likely think of some more commands.

A reminder that the right hand side of this blog contains links to the Home Control 2016 project, ROMs etc.

And now I have this big decision.. whether to spend £1.34 on a PCF-base port expander… which I need to poll regularly if attaching a keyboard – and no spare pins for a beeper – OR to spend £1.68 on an Arduino Nano which can be turned into an I2c peripheral (granted I might need 2 pull-up resistors) with keyboard buffering and a beep facility…..   OR…. go the whole hog and use another ESP8266 to make a completely wireless keypad.

And on that latter note – if you abandoned serial I/O which would net one more output – that gives up to 10 control pins – enough for a keyboard and beeper and light. Hmm…£1.43 for an ESP12, 17 pence for a 0.1” adaptor board.   Fully buffered keypad…. Big decision…

And finally – device 255 is reserved for  a PARALLEL version of this using 6 GPIO pins – 3,4,12,13,15 and 16 – operation is identical. All in the code – including the OTA ROMS. Documented in the WORD manual.

Update: On the right you see a Seeed OLED – I starting with this library, code intended for Arduino, I’ve heavily modified it to run in the normal ESPRESSIF SDK environment – but I have to say – the original Arduino version was SLOW, so VERY slow and this is still a little slow – especially the screen clear – I’ve pulled that into one function with an inner loop of I2c bytes, way faster than the original  but even THEN it is hardly nippy – but the important thing is that “Hello World” works – so soon I’ll add the above commands and then figure out a way to speed it up. Right now I can manage {seeed:”Hello world”} or similar. Current software and ROMs are on the web.