1. Detection Circuit
ENGR
Pre Lab

2. TrimPot Trim Pot Pin 3 to +5V Pin 3 Pin 1 to Ground
Is a potentiometer (variable resistor)
By varying the resistor, it creates a variable voltage source
Total resistance (Pin 1 to Pin 3) = 10 k ohms
Resistance at Pin 2 varies by turning the small adjustment screw ( 0 to +5V on Pin 2)
Is used to calibrate the Binary Voltmeter circuit
Trim Pot
Pin 3 to +5V
Pin 3
Pin 1 to Ground
Pin 1
Pin 2 – Variable resistance controlled by screw
Pin 2

3. Schematic

4. Fluorescein Detection Circuit
The detection circuit performs four functions:
Fluorescein excitation (with a blue LED)
Fluorescein emission detection (green light photodetector)
Converts fluorescence signal from analog to digital
Displays a binary coded value that is proportional to the amount of fluorescein in the detection well

5. Fluorescein Detection
detection well
excitation
emission
Acrylic chip
Side view where Acrylic chip is sitting on top of the DAD
blue LED
photodetector

6. Optical Components Light Emitting Diode (LED) Photodetector
Emits light proportional to current through diode
Two uses of LED:
Blue LED – Fluorescein excitation
Red and Green LEDS are used to display
the “Binary Number” at the output of the
Binary Voltmeter
LEDs are polarity dependent, the short wire has negative terminal whereas the longer wire has positive.
Negative terminal
Photodetector
Resistance that varies with incident light
Sensitive to specific wavelength (Green)
Fluorescein emission detection
EXTREMELY SENSITIVE TO POLARITY!

7. Fluorescein Detection Circuit
Photo-
Transistor
3 wires
DAD
Diode
2 wires
Integrated Circuit
ADC0804

8. Analog vs. Digital

9. Learning Objectives of Lab
Students will learn about –
Electronic circuit components
Building the binary voltmeter circuit from a schematic drawing
Troubleshooting electronic circuits
Binary numbers and binary-decimal conversion