E11 Lab #3
Postlab (Report)
2008

Lab report is due the next time you come to lab.

This lab has a short report. Please turn in your lab report with the parts labeled as the are below (to make grading easier for me).  Note: many of the circuits below look a little complicated - try to make judicious use of Thevenin and other circuit simplifications (e.g., parallel and series resistor equivalents).

1. Part 1: Touch Screen
1. For the circuit below (from: http://www.ni.com/pdf/manuals/371303l.pdf ):

1. Find the output voltage (the wire at the right - connected to an A/D convertor) if the input (labeled "AI") is +10V. (circuit redrawn below - note that this is a variant of the circuit from the first lab)
2. Find the output voltage if the input is changed from +10V to -10V.
3. Find the Thevinin resistance seen by the A/D convertor (i.e., looking from the right towards the left at the three resistors - assume "AI" is an ideal voltage source.
4. Are these results consistent with and A/D convertor with a range of 0 to +2.5 Volts?
2. Turn in the results from table 1 of the procedure.   Explain as well as you can.
3. Repeat for table 2.
4. The I/O box accurately measures the voltage at the Analog input (i.e., the leftside of the circuit below).
1. What is the Thevenin circuit seen looking in the terminals from the left (circuit is redrawn)?
2. What is the value of AI if it is connected to a 5V source through a 10k resistor?  (Note: this is the situation we have when one layer of glass is unconnected).
3. The screen has a resistance of about 400 ohms, so if you touch near the middle you get a situation like the one shown.  Find Vscreen.
4. Now if we try to measure this with our circuit, the whole circuit looks like the one shown.  What is the voltage between the 200 Ohm resistors here?  The difference between this result and the previous result gives you an indication of the error introduced by the measurement apparatus.
5. Turn in the well-documented (i.e., lots of good, clear and concise comments) code from "Program 4" of the procedure,
6. Turn in a copy of your name (or other suitable text or image) drawn on the touch screen.
7. Any extra credit?
1. No display when not touched.
2. Dots connected.
3. Data smoothed.
2. PCB
1. Demonstrate your working PCB to me.
2. Describe, qualitatively, what happens when you turn each dial, and you push the button.

email me with any comments on how to improve the information on this page (either presentation or content), or to let me know if you had any particular difficulties with this lab.