ENGR201 Lab 2018
Lab 3 Verify the Mesh Current Method on a Breadboard & the Introduction of The Light Dependent Resistor (LDR). Due Sep 24, Monday 10 pm.
of this lab:
Be more familiar with the Mesh Current Method.
1. Be able to use an LDR for circuit design.
(use the mesh current method), simulate, and verify on board for all
the voltages and current in the following circuit:
Unbalanced Wheatstone Bridge:
The Wheatstone bridge is used in two ways: (1) to measure the value of
an unknown resistor by comparison to standard resistors, and (2) to
detect small changes in a resistance transducer. Let's use this bridge
to build a 'Shadow Detector' using an LDR.
A photoresistor (or
light-dependent resistor, LDR, or photo-conductive cell) is a
light-controlled variable resistor. The resistance of a photoresistor
decreases with increasing incident light intensity; in other words, it
exhibits photoconductivity. A photoresistor can be applied in
light-sensitive detector circuits, and light-activated and
dark-activated switching circuits.
Parts Required & Circuit Diagram:
10k & 1k LDR
741 Comparator op-amp
9V voltage source
A potentiometer is an electrical component/device that can be
adjusted to provide an on-demand resistance (in a certain range) in a
Picutres of potentiometers and schematic of them can be found in the following figures:
The Light sensor circuit can be found in the following figure. Probably most simple and
interesting circuit to play with. It can be configured as either shadow
detector or Light detector, which means it can detect the intensity of
light. Right now in the circuit diagram it is configured as a Light
Detector, that means the LED will turn on when we show a bright light
over LDR. We can change this circuit as Shadow Detector by simply
swapping the pins 2 & 3 of 741 Comparator IC, and then LED will
turn on when LDR is dark. In this circuit, please make sure that pins
no 1,5 & 8 are not connected and left idle. Pin 6 is output pin. In
the circuit it is connected to an LED via 1K resistor, but you can also
connect a transistor to turn on a relay, motor or any other output.
Show the results in your report.
** The shadow detector circuit is borrowed from 'Rookie
** Report your results (with figures and texts) on the website.
Follow the lab
to avoid losing points.