GSI: Andy Wang WED 2-5 EE16A Lab: Touchscreen 3 LA: Ashley ...ee16a/fa16/lab/... · WED 2-5 GSI:...
Transcript of GSI: Andy Wang WED 2-5 EE16A Lab: Touchscreen 3 LA: Ashley ...ee16a/fa16/lab/... · WED 2-5 GSI:...
EE16A Lab: Touchscreen 3WED 2-5
GSI: Andy WangLA: Ashley, Carol, Eric
Last Week: Resistive Touchscreen
✘ Touching the screen yields a voltage we can measure
✘ Have to push hard enough to make contact
✘ Need to take one measurement for each coordinate
✘ No multi-touch
Capacitive Touchscreen
✘ Touching the screen changes the capacitance✘ No moving parts✘ Multi-touch is easy
How to measure capacitance?
Measuring Capacitance
Discharge everything by closing clean switch:
Measuring Capacitance
Charge touchscreen ( + finger?) to a known voltage
Measuring Capacitance
Share charge with known capacitor:
Op Amp as a Comparator
Essentially does:if V_in > V_ref:
return V_ddelse:
return 0
✘ Student-built circuit from this semester’s EE 16B ----->
✘ Wires are straight and as short as possible
✘ IC’s (black chips) placed across middle of board so each side of pins is disconnected from the other
✘ Power supply connected to blue (-) and red (+) rails
Clean Circuits!
Notes
✘ Materials handed to you: 2 copper strips, glass slide, tape
✘ Entire circuit grounded by same ground
✘ Use multimeter to measure capacitance
✘ Peel off tape from copper strips
✘ HW7 #5 Part d
✘ Finished capacitive touchscreens on TA desk as examples