multiple capsense input and multiple AVR chips

hello everyone I'd like to make a small project that requires more than 30 touch input, a sort of touch keyboard. I only need to know if the input is pressed or not, I don't need a variable value. Since I'll make the pcb/soldering job on my own, I can only use a PDIP Atmega chip, like the one on Arduino UNO R3, but since I need lot of inputs, I will use something like 2 or 3 of those chips on the same pcb. That would cost less than every other dedicated "touch sensing" ic. Of course I will use ICSP for every chip to program them. My questions are: 1) is CapSense reliable enough for such application? 2) If I use the internal oscillator for those AVR that should only detect the touch, the CapSense would still work well? 3) if I don't use an external oscillator, can I still obtain reliable communication between the AVRs using the serial connection? 4) alternatives?

thank you Dimitri

I've found the MPR121 Capacitive Touch Sensor chip, made by Freescale, to be a better choice for my project. It has 12 touch inputs and works on I2C. on the Freescale website I've read that it is possible to made a 5x7 button matrix using only 1 chip. How can this be done?

1) is CapSense reliable enough for such application?

No.

3) if I don't use an external oscillator, can I still obtain reliable communication between the AVRs using the serial connection?

No.

4) alternatives?

Use a real cap sense chip.

That would cost less than every other dedicated "touch sensing" ic.

No that is rubbish.

thanks for the sincerity, I didn't imagine that the CapSense method is so unreliable. that will bring me to the MPR121 for sure. I should understand how can I arrange the input in order to make a 5x7 matrix, so I can understand how many of those chips I need.

that will bring me to the MPR121 for sure.

It is not the only chip in town:-
http://uk.farnell.com/jsp/search/browse.jsp?N=2031+204541&Ntk=gensearch&Ntt=cap+touch&Ntx=mode+matchallpartial

However having a 5x7 matrix of cap sensors is pushing it. I think the largest matrix chip I have see is 30 individual pads.

yes but it's the only one I've found on a breakout board, since I can't solder those tiny chips. What do you mean pushing it? a 5x7 matrix is on the example datasheet, but it doesn't explain how to accomplish that.

yes but it's the only one I've found on a breakout board,

Well it's not a breakout board it is a development kit

since I can't solder those tiny chips.

It is not as hard as you might think, a good pair of tweezers and a magnifying visor and anyone can solder surface mount chips. Also look for blank PCB adapter boards to help you. Ebay has them quite cheap.

no it's actually a breakout board sold pretty cheap on Sparkfun.. yes it's not a problem soldering SOIC or SOP packages or similar, but those touch sensor chips with multiple inputs actually only came with smaller packages..

Have you seen this:- http://uk.farnell.com/jsp/bespoke/bespoke7.jsp?ICID=I-HPBL-LTOFF-0203&bespokepage=farnell/en_UK/promotions/lp/campaign/cypress-psoc4.jsp It is a processor with cap senses built in.