[Arm-netbook] IC for analog and digital buttons (EOMA-68)

[krasi gichev]

I suspect that we are not looking at the complete picture here. Don't you
have some more sensors to add on the I2C? Like accelerometer, magnetometer,
maybe light sensor (for auto brigthness) and so on? Maybe battery
monitoring?
I see that you are discussing about using I/O expanders and ADC chips. Not
to say that IN YOUR CASE you have to use microcontroller - just to show
some points that could help you to take the right decision. .
Using I/O expander means that you need several chips - at least two. This
will take some board space and pin connections. Don't forget that beside
I2C lines (SDA, SCL) you might need some (maybe one, maybe two) interrupt
lines. Some clock lines in addition? Also, those simple chips will force
you in scanning very often (1ms, 10ms?) about actual data.
Using microcontroller is not easy, that's right. But don't forget that it
adds a lot of flexibility. Most modern microcontrollers now have built-in
(ROM) bootloader with support for UART, SPI, I2C and so on. I would propose
STM32 for example (it is quite well supported by open source tools and code
base).
You get low power, low latency processing core - think of filtering, post
processing, event detection. Yes, you need to manage firmware update - but
this is just because IT IS POSSIBLE to do on the field update (vs fixed
function I/O expanders). Some manufacturers (e.g. microchip), and
distributors allow ordering chips with pre-programmed user firmware - so no
need for programming equipment or JTAG port on the board.
I could imagine that in your case you might even use the microcontroller
without precise crystal/ceramic resonator - just with built in RC
oscillator (1-2% precision but this does not matter on I2C).
The code itself will not be much of an issue - I suspect that this will be
open sourced too so you can get a lot of help on this. So called "sensor
fusion" is quite close to your application.

I haven't used yet any of LPC line of Cortex-M microcontrollers from NXP,
but I like one of the features - every signal from internal peripheral
could be mapped to any microcontroller pin. This means several things:
- you can use all functionalities (internal blocks) without conflicts
because of pre-defined "alternative function" mapping - usually this means
that you get the smallest possible package to solve your task
- you get the flexibility to change pin mapping later - when the board is
ready (but 2 pins were swapped ...)
- you can change pin mapping in runtime - think of using some pins as UART
at power on, then switching to I2C

If you have a space USB port on the EOMA, you could put the STM/LPC on the
USB. Than use the ready made USB HID examples and feed in your data. Than,
use the whole input infrastructure of linux/android and get your events -
without coding on the Linux side? (don't know if this is true, just
speculating).


2014-08-04 14:14 GMT+03:00 Luke Kenneth Casson Leighton <lkcl at lkcl.net>:

> On Mon, Aug 4, 2014 at 11:22 AM, Miguel Garcia <gacuest at gmail.com> wrote:
>
> > There are 2 options for the controls:
> > - Use MCP23017 (for the 19 digital buttons) and MCP3004/8 (for the 6
> > ADCs, we must look if we can use the model finished in 4 or we have to
> > use the model finished in 8). This option is easier to program, but I
> > suppose that it's hard to design the PCB (it's 2 IC).
>
>   it'll be pretty straightforward.  also you have the advantage that
> you can separate the analog ADC IC from the digital one, separate the
> ADC IC with some ground protection and you'll get less noise.
>
> > - Use a microcontroller like ATtiny48 (for the 19 digital buttons and
> > the 6 ADCs). This option is more difficult to program, but easier to
> > design the PCB (it is one IC).
>
> > What is your recommendation?
>
>  honestly i'd go for the less difficult to program option, straight
> away.  you're not on a huge cost-saving exercise so it's fine.
>
> l.
>
> _______________________________________________
> arm-netbook mailing list arm-netbook at lists.phcomp.co.uk
> http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook
> Send large attachments to arm-netbook at files.phcomp.co.uk
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.phcomp.co.uk/pipermail/arm-netbook/attachments/20140806/60aa16e6/attachment.html>