-> Ok, got it! ( sorry for the whoopsy ;/ )

-> Yup, using Js for such things is just awesome ( Nb: I still can't get my hands on any canvas renderer for OpenJsCad, & may be looking on Three.js & ThreeX.js plugins to get that functionality ( I wonder if we could have the best of both world, aka parametric mesh in real time ( thx to OpenJsCad ) with canvas renderer & other niceties ( animation, .. ) thx to Three.js )
=> also, a dedicated controller on an Espruino controlling the so-called mesh parameters 'd neat ;)

I actually had some tests in mind to do with some ATtiny85, but as you said I2C is not fast enough for some needs ( .. )

=> for the iPad/Android phone/tablet part, I guess we don't have any access to BLE peripherals from a WebView :(
This being said, using the HM-10 BLE ->UART i a neat idea indeed!

Also, I have some updates [ that still need updates :/ .. ]:

-> I had littl' tile to test the headset jack <-> Espruino UART thing, and ..
.. I couldn't get it to work with neiher my iPad, an android tablet, nor my computer :/

• for the iPad, this may be normal, since WebAudioAPI requires iOS7 & above ( see I guess I'll have to upgrade my 5.1, & it well as migh bring WebGL to mobile Safari if I'm not wtong ( gotta check caniuse .. ) ;p )

• for the android tablet, it may come from the OS version ( 4.0 ), since WebAudioAPI are supported in Android Chrome 39

• I got an Android phone ( GooPhone ;p ), but the results are the same :/

• for my computer, it supports WebAudioAPI, but I've seen that it seems to detect the TRRS cable for headset & microphone only when I don't plug it fully-fully ( may come from the jack entry used, but that's what appeared in the Ubuntu Audio Prefs :| )

Nb: for all the above devices, I even tried typing " javascript: audio_serial_write('LED1.write(0);'); " but no success either with it

Also, worth mentionning, the webpage I used is hosted here:
madtoyslab.com/Espruino
( when trying one of the procedures exposed in EspruinoOrion, I only get glitches in the "console-like" page )

Not knowing if the trouble was coming from my wirings or the tiny circuit I did build [ in hurry ], I did a tidier version of your circuit on a breadboard, & made another jack plug as mentionned ( both are using TRRS to have 2-ways comm possible ), but it the result is the same as the tiny version :/

I am willing to backup the iPad I got & do that *** update ( if I get WebGL for OpenJsCad on it, it seems fair .. :/ ) & retry my tests when I got this damn mobile Safari WebAudioAPI support, but just in case, I didn't clearly get where I'd put a 10 uF cap ( would you please point it in one of the breadboard pics ? :) )
=> this may help to re-do my tests on the different devices ( .. ) :)

I also post some pics I took when building the 2nd version of the cable in case it may help someone [ and that maybe one of the forum member 'll take the time to add a tut with them on how to have jackUART with Espruino [ & links to a "standalone" code for the 2-way comm' ] / be added to the EspruinoOrion github page, for clarity's sake ]

If I can, I'll be back right after doing that pad update, to tell you how it went ( .. )
Last but not least, the firmware update from the Espruino IDE worked flawlessly ;)

** Espruino headphone jack as UART using a TRRSplug **

** tiny [tidy on the front / not on the back ] version **

** breadboard version **

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