touchscreen interfacing

Look up the UCB1400 at the NXP (Philips) web site. This is a cool little part in an LQFP49 package that has an inbuilt touch screen controller that will hook right up to your Y-, X-, Y+, and X+ pins. The controller side interface on the other side of the part is a serial link interface which you can easily control from your MCU.

- mkaras

Hi,

Thanks I found lots of IC's that interface to Y-, X-, Y+, and X+ touchscreen pins with SPI and I2C interface:

analog devices: AD7843 AD7877

maxim: MAX1233-MAX1234 MXB7846

ST: stmpe811

TI: ads7843 tsc200x

cheers, Jamie

You have 4 GPIOs, and 2 analog inputs. (If the GPIOs can also be analog inputs they can be the same).

- switch the IO's to put a voltage across Y+,Y- - switch X-, X+ to input mode - read Y coordinate from analog input connected to one of the X's

- switch the IO's to put a voltage across X+,X- - switch Y-, Y+ to input mode - read X coordinate from analog input connected to one of the Y's

You also need to detect the case of no-touch, where your input will be floating with the above scheme. Possibly a weak pullup to +ve; this will generate a voltage outside the normal coordinate range.

Don't forget to have some protection against ESD and other noise spikes. E.g. TVS diodes followed by resistors or ferrite beads.

Or you can cheat and buy a chip to do it...