Hi, > Anybody used a touch screen before over an LCD display? Got any interface > PIC code? I have done this too. If you are using a 4-wire touchscreen it does in fact operate as you inferred. I was using a custom micro, with a 10-bit ADC (sort of- it was a DAC and a comparator on-chip). As you say, you have to set up a voltage gradient on one side of the resistive pad and read the voltage off one of the connections on the other side, then swap the voltage gradient and readout pins. There are a couple of pages about this in the Dragonball application notes from Motorola. A word of warning: some resistive pads have a low surface resistance, of the order of a few hundred ohms. This means that the I/O's on your micro may not be able to sink or source the current needed to set up the voltage gradient as it could be 10mA or more, so you might need driver transistors. Also the input impedance to the ADC must be very high (which they typically are) otherwise you will get a voltage drop on the pickup side, and if your ADC does not work rail to rail then you might need four extra resistors to narrow the voltage range across the pad. Finally, resistive touch screens don't work very well with fingers. For best result you need a stylus, or use your fingernail. Andy -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements