I like the idea of the resistor matrix. I might have copied it if I hadn't gone a different way already.

This little board from Sparkfun can do up to an 8x8 matrix, has debounce built in, uses I2C, and has an output that can be connected to an interrupt.

https://www.sparkfun.com/products/13601

On Mon, Jun 25, 2018 at 09:24 am, Arv Evans wrote:

Jerry

Thanks for the info.  I did a quick scan of the relevant pages. I can see several possible

uses for this device.  Maybe I missed something but it seems that  like almost all I2C
devices it is a true slave and thus does not automatically assert bus control to signal that
an event has occurred.  Possibly I would need to re-read the datasheet in detail to affirm
this if my design effort takes me in that direction.

 

Arv
_._

On Mon, Jun 25, 2018 at 10:05 AM Jerry Gaffke via Groups.Io <jgaffke=yahoo.com@groups.io> wrote:

Here's a datasheet  (sort of, you don't get the pdf):  https://pdf1.alldatasheet.com/datasheet-pdf/view/810501/TONTEK/TTP229.html
Bottom of page 8, section 3-4 describes the 2 wire interface, though not very clearly.

They say SDO is always out, SCLK is always in.
And that SCLK can be anything between 1khz and 512khz when scanning.
A pause of 2ms on SCLK resets the interface for the next scan.
They apparently have a way to just check the state of SDO occasionally to see if any key was pressed,
though I find the datasheet tough to read on exactly how this works.

The chip also implements full i2c mode, also various parallel modes,
though not clear what modes any particular keypad using the chip would support.

Jerry


On Mon, Jun 25, 2018 at 08:38 am, Robert McClements wrote:

Arv,

The TTP229 capacitive  keyboard has two pins labelled SCL and SDO but unfortunately they are not I2C.

The way that they work is SCL is clocked frequently up to 16 times and during each clock cycle SDO is
checked. If a key is pressed SDO will return a Low, the count stops and the clock count equates to
the key number. Hope that makes sense, not easy to put into words.

So this device will require the use of two digital pins.


Regards,

Bob GM4CID