Lexmark Non-Contact Edge Detector Weekly Update Meeting (March 9, 2011)

Circuit Testing of Last Semester’s Final Product Connected power to circuit and measured voltage at emitter of upper level detector Obtained square wave of fan moving in/out of field of view, creating positive and negative triggers at output (i.e. input to the printer’s ASIC)

Conforming Results Output shows that fan is causing a break in the optical path. Voltage buffer (before output) does force analog signal to a digital high or low. Digital high or low configures to a voltage difference of ~5VDC. Freq = 39.7Hz yields Period =.0251sec Distance of Period = 2 in yields Traveling Speed = 79.4 in/sec *NOTE: Although design can detect faster than 70 in/sec, fan variability greatly reduced at higher voltages (can become unreliable and unsafe very quickly). Rising time on output = microsec yields Distance traveled for transition = in yields Distance in mm =.0797 mm Device met requirement of must sense a change in transition level within.1 mm.

Non-conforming Results Circuit analysis shows that extra jumper added to short out feedback portion of calibration circuit (turning op amp into a unity gain buffer). This puts a constant voltage on the LED. Lack of variability makes the photodiode and hence calibration circuit void in the system. Tests showed that with original circuit (jumper removed), not enough photocurrent was produced to drive the LED (in the range of 100’s of mV). Thought process behind calibration circuit must be rethought and redesigned.

P-Spice Simulation of Ideal Photocurrent Photodiode replaced with a current source of 25uA Simulation produced 1.622V at LED Voltage is at correct level to turn on LED 25uA 1.622V

Photodiode replaced with a current source of 10uA Simulation produced 5.657mV at LED Voltage cannot overcome breakdown region of the LED P-Spice Simulation of Likely Values for Photocurrent 10uA 5.657mV

Photodiode Characteristic Test Tested characteristics of photodiode with IR LED pointed directly at the sensing surface of the photodiode. Emitter and detector placed next to each other for maximum optical output at the detector. Blocked ambient light to photodiode to limit photocurrent produced by other sources than the IR LED. Varied voltage on LED in a range of 0V – 1.3V. Probed voltage across resistor in series with photodiode. Used 320K Ω resistor as max but also used a variety of ranges from 7.5KΩ to the max in testing.

Photodiode Results Voltage (LED power) Voltage (Photodiode Resistor) VDC0 mv 1 VDC25 mv 1.06 VDC193 mv 1.18 VDC317 mv 1.3 VDC372 mv Results reflect the usage of the 320KΩ resistor. This resistance produced the maximum amount of voltage across the resistor (lower resistances peaked in range around 200 – 300 mv). Increasing applied voltage to the LED had a result of moving the voltage across the photodiode resistor towards 400 mv. An increase in resistance tended to coincide with a larger voltage but eventually had an effect of reducing photocurrent. LED would malfunction before proper amount of photocurrent could be made to drive an LED (in the 1.2V region).

Paper Translation Assembly Isometric DesignSide View

Other Tasks Update of project website SyRS rev. 1 completed Meeting with Dr. John Naber to discuss the applications of photovoltaic op amp circuits and subsequent research