Re: Microcontroller (AVR) programming from smartphone

Hi Friends! First of all thanks for all those replies. These are my first steps in usenet and I hardly expected such quick and multiple-sided discussion. Seems like some suggestions complement each other so I'll answer in the order of encountering them in replies.

A worthy project for your students, and the solution could be used around the world!

Thanks for your kind words. Actually it already can be used but probably I need to add more documentation/video, particularly about hardware setup. "Coding / beeping" page is here (you may click "compile" and then "burn" just for fun):
https://rodiongork.github.io/avr-mic-loader/
Setup may look as easy as here:
https://i.imgur.com/j6N3aNe.png

Presumably, you want this to be an interface that each student can "take

home"
Yep (some of them already took it home and did some coding in "unsupervised" mode), moreover it would be fine to have interface which is easily and cheaply reproducible.

some control over the MCU-end of the system.  Is this an

OTC "module"?
I'm not sure what is OTC module. AVR microcontrollers were picked as those with probably simplest assembly language, particularly these are bare ATMega8L chips in DIP-28. Initially kids plugged them into breadboard, added battery, couple buttons and LED - and audio-connector of course - and voila (see image linked above). That was not very stable so we invested 2-3 lessons in building hand-made PCBs.

Look into the "Kansas City Standard"

Thanks, I glanced over but need to dive more into details. It also reminded me of approach used with ZX spectrum, need to check how exactly it worked...

I would assume you really would like a bidirectional link.

Well, this would be an improvement though more wiring is needed and audio port with mic input. Shall search for more info how 4-contact jack is implemented on various smartphones... Though if uploading could be made more stable even with one-way link, I'll stick to it for simplicity...

If every phone supports a microSD card

Surprising idea! never came to my mind, though I think there is no API to directly control SD card pins and with 8-bit MCU bootloader it is probably not possible to accomodate for complicated code handling SD card IO... And yep, these are perhaps more rare than audio jacks

The USB charging/data port would be another obvious candidate

Unless I'm mistaken it works only with phones which have USB "on the go" variety, e.g. can work as USB-host?

A BT interface on your MCU module

We actually did use this previously (HC-05 or something alike), just with somewhat different firmware (also created by me) allowing an interactive BASIC on Arduino or STM32. Here is a lousy video:
https://www.youtube.com/watch?v=q9JcWGs_VaI
However setting 15+ cheap bluetooth devices with shaky power supply - they were not working fine
and it was sometimes painful experience. I admit I haven't thought of them for uploading though
it will make straightorward flow. Perhaps shall switch to it if "audio" channel couldn't be
improved after all, thanks :)

You can also hack the NFC interface

Here I'm a bit out of sync with technology - does all modern smartphones include NFC? And I think receiver needs a chip like 531 or 522 and some stuff around so it feels bit too complicated for school level...

The (camera) "flash" LED might be easy to drive

Very curious idea I completely missed, also not sure about throughput but need to go and check first. Also it suggests using camera itself as a feedback... very interesting!

you could paint a barcode image on the phones screen

Ha-ha! that is also something I completely missed. I can easily program "running barcode" in an HTML page with javascript/canvas... Not sure if it will work better than blinking display, but
it looks much more comprehensive to user... and seems more versatile (even up to printing barcode on a paper) - will think more about this, thanks!

Maybe play a suitable (uncompressed?) video with bits encoded as frames?

Don't ask me how, just a thought.
That may be working, right. Not necessarily video, it is possible to programmatically blink an area of screen etc...

Keep your audio interface but plug it into a Bluetooth audio receiver

Interesting, never thought of this approach - shall investigate it further, thanks.

Maybe they could upload the code to a web site, and you could have

hardware in the student lab that loads the target machines
funny, but you described exactly approach we used year ago - they uploaded code to my server, then rushed to the single laptop at the center which had USB programmer attached - and here entered pin-code by which small script fetched the compiled HEX-file from the server and uploaded it. It was just not very convenient when there are many people and few (or single) computer. But it was the most stable setup probably, that's true.

Coding on a phone sounds nasty.

I agree. But coding without anything is even worse. These are "facultative" classes of electronics happening once per week and we can't pretend on supplying ourselves with suitable auditorium with desktop computers or fetching dozen-or-two spare laptops :)