Report by Guy Lee, last update 4/3/06

Unfortunately, the datasheet has poorly 2-page information. For more detail, I have to take a deeper look at Touch Screen Reference Desogn. In "Hardware Setup" chapter of this datasheet, I get an information which is likely what I needed for touch panel pins.

This picture shows how a touch panel connects to the evaluation board:

And here is the close look at the touch panel pins:

Because the LM8000 reference design comes with a 4-wire touch panel, which is said Panasonic EMU601A2 on website, and also, after taking a close look at the panel, I assume that some pins are useless.

Analog vs Digital

Left is digital touch panel which only senses ON/OFF mode and right one is what I get, Panasonic EMU601A2, which can also sense the pressure by resistive change.

[Test]

Here is my circuit:

[PicBasic code] 


DEFINE OSC 4

' Define ADCIN parameters
' Set number of bits in result
DEFINE  ADC_BITS        10 
' Set clock source (3=rc)
DEFINE  ADC_CLOCK       3   
' Set sampling time in microseconds
DEFINE  ADC_SAMPLEUS    10        

TRISA = %11111111 
ADCON1 = %10000010

tx var portc.6
rx var portc.7
n9600 con 16468
output portb.7

channel var byte
adcVar var word[4]
xVar var word

main
    high portb.7
    for channel = 0 to 3
    adcin channel, adcVar[channel]
    serout2 tx, n9600, ["porta.", DEC channel, "= ", DEC adcVar[channel], 9]
 '   pause 50
    next
    'xVar = abs(adcVar[0]-adcVar[1])
    'serout2 tx, n9600, [dec xVar,13]
    'pause 1000
    serout2 tx, n9600, [10,13]
goto main

Questions

  1. It seeems that the numbers jump irregularly but do react to my touch. And the change seems to react to the pressure.
  2. I tried wheatstone bridge and aso ampifier, but they didnt help.