Objective: Convert an LTSpice schematic to breadboard components and light an LED.
Skills learned: How to construct a circuit using a breadboard and nScope.
Deliverables: Answer the questions on this page and turn it in on Canvas. Be sure to take pictures of the circuits you create and what you see on the nScope.
Score: This lab is worth 43 points
Breadboard
From: http://wiring.org.co/learning/tutorials/diagrams/index.html
http://wiring.org.co/learning/tutorials/breadboard/
Strips of metal underneath breadboard holes connect rows (A) and columns (B). However, you cannot plug in a component so that both wires are in the same column, otherwise you will burn out the component.
Use wires to connect supply lines, columns, and ground lines to allow current to flow in the circuit.
LED driver circuit
Light Emitting Diodes (LEDs) are directional meaning that current can only flow one way. The positive side (anode) will have a longer leg than the negative side (cathode) and be placed in the circuit so that the anode is connected to the 5V power source and the cathode is connected to ground.
Red LEDs in particular have a unique biomedical application as they are used in pulse oximeters to measure the oxygen saturation level in the body. This is done by detecting the light absorption of oxygenated and deoxygenated blood.
1. LEDs have a maximum current that can flow before they start to burn out. Look up the maximum allowable current for a standard 5mm diameter LED. Report back the answer. (1 pt)
2. Calculate the resistance needed so that the current is 90% of the maximum allowable current so that the LED won’t burn out. (2 pts)
3. Connect the LED as shown in the schematic above but change the resistor values. Report back the calculated currents, voltage measured on the nScope between the LED and resistor compared to ground, and photos of LED brightness. (10 pts)
Resistance Vout Calculated Current
220 Ω
1 kΩ
10 kΩ
1 MΩ
Place picture of the circuit here
4. To dim an LED without changing the resistor, pulse width modulation signals are used. (5 pts)
Using the nScope, use the P1 channel as the pulse output channel. Turn on the P1 channel and use that instead of the 5V power source.
Change the frequency and duty cycle so that the LED appears to be constantly lit instead of blinking. Adjust the duty cycle to be 20%, 50%, 75%. Take photos and comment on what you observe. (10 points).
Voltage Divider Circuit
You will need to use LTSpice to complete this lab. If you haven’t downloaded it please do so now.
https://www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html
Construct a voltage divider in LTSpice as shown below.
1. Measure the simulated voltage across a 1k resistor as you vary the current through it. Change the value of “R1” so that you get different values for current through R2 and fill out the table. (5 points)
R1 [Ω] VR2 [V] IR2 [mA]
100 4.54545 V 4.54545mA
330
10k
1M
(a)
2. (b) Wire a voltage divider using the circuit components and breadboard. Measure the actual output voltage between R1 and R2 compared to ground using the nScope. (5 points)
R1 [Ω] VR2 [V] IR2 [mA]
100 4.54545 V 4.54545mA
330
10k
1M
3. (c) Calculate the percent error between the simulated values and the measured values. Comment on what you observe. (5 points)
R1 [Ω] % error VR2 [V] % error IR2 [mA]
100
330
10k
1M