Practice circuit: making a Wheatstone bridge in TinkerCAD

Summary

In this video, Dr. Dan demonstrates how to build a Wheatstone Bridge circuit on a breadboard. He explains the basic components of the circuit, including resistors, a potentiometer, and a photoresistor. The Wheatstone Bridge is used to measure resistance by monitoring the output voltage. Dr. Dan also shows how the circuit can be used as an instrumentation circuit, such as for measuring light with a photoresistor. Through a step-by-step walkthrough, he illustrates how to set up and test the circuit to measure small voltage changes related to varying resistance.

Takeaways

• 🔋 The video demonstrates building practice circuits for BME214L, focusing on a Wheatstone bridge.
• 🛠️ A Wheatstone bridge uses four resistors to measure an unknown resistance through voltage output.
• 📏 Components used include three fixed resistors, one variable resistor (potentiometer or sensor), a 9V battery, and a multimeter.
• 🔴 Positive battery terminal connects to a node shared by R1 and R3, and the negative connects to the node shared by R2 and Rx.
• 🎛️ The potentiometer's wiper arm is critical for measuring variable resistance as it allows voltage variation with position.
• ⚖️ When all resistors are equal (1 kΩ), the bridge is balanced and the output voltage (Vout) is theoretically zero.
• 💡 Replacing the variable resistor with a photoresistor allows the bridge to function as a light sensor.
• 📊 Voltage across the bridge is easier to measure than resistance directly, translating sensor changes into readable voltage.
• 🎨 Color-coding connections (red for positive, black for negative, blue/turquoise for Vout) helps visualize and organize the circuit.
• 🔬 Wheatstone bridges are commonly used in instrumentation circuits, including sensors like thermistors, strain gauges, and photoresistors.
• ⚡ Simulation shows that small deviations (e.g., 1 mV) occur due to practical imperfections but are negligible for measurement purposes.
• 🎯 Adjusting the potentiometer to midpoint gives Rx ≈ 1 kΩ, demonstrating how bridge balance works in practice.

Q & A

What is the purpose of the Wheatstone Bridge circuit demonstrated in the video?

The Wheatstone Bridge is used to measure the resistance of an unknown resistor by measuring the output voltage, which changes based on the resistance of the components in the circuit.

What components are used in the Wheatstone Bridge circuit shown in the video?

The circuit uses four resistors, including a variable resistor (potentiometer) or a photoresistor in some cases. It also uses a 9V battery, a multimeter for measuring output voltage, and a breadboard to assemble the circuit.

How is the circuit powered, and what is the role of the 9V battery?

The circuit is powered by a 9V battery. The battery provides the necessary power for the circuit, allowing current to flow through the resistors and enabling the measurement of the output voltage.

What is the function of the potentiometer in the Wheatstone Bridge?

The potentiometer, or variable resistor, allows for adjustable resistance. By turning the potentiometer, the resistance changes, affecting the output voltage, which can be used to determine the unknown resistance.

Why are resistors labeled in the video, and what are the labels for the resistors used in the Wheatstone Bridge?

The resistors are labeled to make it easier to reference them during the circuit explanation and design. In the video, the resistors are labeled as R1, R2, and R3. The potentiometer is referred to as RX, representing the variable resistor.

What is the significance of the 'V out' measurement in the Wheatstone Bridge?

The 'V out' measurement represents the output voltage that changes depending on the resistance in the circuit. By measuring this voltage, the resistance of the unknown resistor can be determined.

How does the potentiometer’s position affect the Wheatstone Bridge circuit?

The position of the potentiometer determines its resistance. When the potentiometer is set to one end, the resistance is close to zero, and when set to the other end, the resistance is close to 2 kilo-ohms. In the middle, it is about 1 kilo-ohm.

Why does the output voltage not reach zero even when the resistance is balanced?

The output voltage may not reach exactly zero due to slight imperfections in the circuit or measurement, like small voltage drops or noise. The video shows a 1 millivolt output, which is quite small but not zero.

What is the advantage of using a photoresistor in the Wheatstone Bridge circuit?

Using a photoresistor allows the Wheatstone Bridge circuit to function as an instrumentation circuit for measuring light. The resistance of the photoresistor changes with light intensity, and the output voltage can be used to measure the amount of light.

Can this Wheatstone Bridge circuit be used with other types of resistors, and if so, how?

Yes, the Wheatstone Bridge can be used with other types of resistors, such as thermistors or strain gauges, which also change their resistance in response to environmental conditions like temperature or strain. The output voltage would change accordingly, allowing measurement of those physical changes.