Here is an app note from Atmel describing how build DIY touch keys using Philipp springs (or any spring made from conductive material) and their qTouch ICs. This design allows PTH LEDs to be mounted inside the keys.
The Philipp™ spring is a simple and cost-effective method of creating a touch key on a dielectric front panel such as glass or plastic, using a conventional PCB behind the panel. The method connects a pad on the PCB to bridge a space of up to a few cm of air gap to the rear of a dielectric panel to form an electrode.
It’s worth to note that Atmel have a patent on using Philpp springs as part of a capacitive touch sensing assembly – they grant you a license to use it if you use their touch-sensing ICs, but if you aren’t it’s a good idea to stay well away if you are making something commercial.
Capacitive touch sensing is a nightmare for patents. It’s not just Atmel that have it tied up – Microchip and Cypress are pretty active in the IP arena as well.
(source – I do this for a living…)
thanks for the headsup AJ, I had no idea about that stuff.
this i2c chips look actually very nice (for e.g. AT42QT1070), 7 buttons, interrupt pin, i2c bus .. ability to run in “stand alone” mode (4buttons only then) … very interesting, the problem I find is that datasheet is “typical atmel datasheet”, it contains almost nothing there :(
AT42QT1070 is $1.5 when purchasing single chip looks great http://www.atmel.com/Images/doc9596.pdf but all the info on how to design PCB, how to design BUTTONS is missing .. datasheet show some basic schematic … look at the story about Rs .. they say “series resistance is required to reduce noise, should be approximately 4.7 k to 20 k ” .. cool, when is good to have 4 k and when is better to go with 20 k, etc etc etc ..
Check for e.g. mchip’s documents:
http://www.newark.com/pdfs/techarticles/microchip/01334A.pdf
http://www.microchip.com/stellent/groups/SiteComm_sg/documents/DeviceDoc/en542979.pdf
Is there anything comparable from Atmel? (cause I like these i2c chips more then integrated solutions)
I found something similar: http://www.atmel.com/Images/doc10752.pdf
Moin
Just a short side note: You don’t need an extra chip for capacitive touch sensing.
It can be done with any controller that has at least 2 tri-state pins, which can be configured as output or input by software.
A German tinkerer know as Zabbex has documented it here : http://www.zabex.de/site/schaltungstechnik.html#kanmi2.
The google translation sounds a bit odd due to the informal writing style
http://translate.google.com/translate?sl=de&tl=en&js=n&prev=_t&hl=de&ie=UTF-8&layout=2&eotf=1&u=http%3A%2F%2Fwww.zabex.de%2Fsite%2Fschaltungstechnik.html%23kanmi2&act=url
but the basic principles should become clear, when looking at the illustrations.
As he states this method was inspired by Atmels Q-Touch software solution, so there is a patent problem here as well.
I’ve tried this myself some time ago and it worked surprisingly well.
I could even get reliable reading through 2cm thick wood or 1cm acrylic glass.
Greetings
Sebastian
Most today’s mcu’s have some touch interface themselves so no need to use up 2 pins for a button, the point is to use mcu pins for bit more important tasks then to drive buttons, use el-cheapo (like AT42QT1070) on the button panel directly and just take i2c bus to the mcu.. you get some port expander on i2c to turn leds on/off, some i2c port expander for switches, some qtouch for buttons and you can have as complex front panel as you want fully controlled via 2 line i2c :)
Is I2C ok, for buttons, I mean it is master controlled so there would be no interrupt control right? Isn’t UART better for buttons, you also have 1 wire just TX(from the buttons), not including PWR and GND, you can easily built it with a pic a cheap 20pin pic16f…Although that would take more development time, as you would need to write firmware for the front panel as well…But I guess it would even out to the time it takes to figure out the Atmel datasheet :D
…ups didn;y see that the atmel IC has a change pin which could be used for interrupt handling,
i2c is better then usart, the i2c expander has the interrupt pin that will ping you when you have any changes, usart uses too much time and resources. So if you have for e.g. 20 buttons you put 4 of those button drivers on the i2c bus + one i2c port expander. Link interrupt lines from button drivers to port expander and interrupt from port expander to mcu. When you get interrupt on mcu you ask port expander what driver had the interrupt, then ask driver what button was pressed :D This uses only the i2c on the mcu + one interrupt line and can be used to drive as many leds, switches and buttons you like
Hi, i am using these Atmel chips and for the capacitive sensor i really need these.
Where can i buy these springs from ? I searched eveywhere and i could not found them :-( …
Thanks in advance for any help/info !
Rgds. Jorge
Hi, somebody know where can buy metallic spring for capacitive sensor?
Thanks
I’m searching in website without any results…
Thanks again
Try Fasttech, go there and look for spring parts for torchlights, under the torchlight section.