Basics calculator
Wheatstone bridge
Two dividers side by side: when they match, the output is zero, whatever the supply.
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The example, worked out
Given
- I want
- The output
- Excitation
- 5 V
- R1 (left, top)
- 1 kΩ
- R2 (left, bottom)
- 1 kΩ
- R3 (right, top)
- 1 kΩ
- R4 (the sensor)
- 1.1 kΩ
Working
- two dividers
- the difference between the middles
- the ratios equal, the output is zero
Results
The formulas
- Vout = Vex × (R4 / (R3 + R4) − R2 / (R1 + R2))the difference between the two middles
- balance: R1 / R2 = R3 / R4then the output is zero whatever the excitation
The usual traps
- The output is not linear in the sensor resistance: compute the resistance back for wide swings.
- The excitation warms the sensor arm: lower it, or pulse it.
Questions
How do I calculate the output of a Wheatstone bridge?
Vout = Vex × (R4 / (R3 + R4) − R2 / (R1 + R2)): the difference between the two middles. balance: R1 / R2 = R3 / R4: then the output is zero whatever the excitation.
What does it give for typical values?
119 mV out of 5 V with 1 kΩ, 1 kΩ, 1 kΩ, 1.1 kΩ. Output B − A: 119 mV.
What are the usual mistakes?
The output is not linear in the sensor resistance: compute the resistance back for wide swings. The excitation warms the sensor arm: lower it, or pulse it.
In the app
Your circuit, drawn live
Change a value: the schematic redraws with your numbers on the parts.
The part you can buy
Results rounded to standard values (E12, E24, E96) and power ratings.
The working, shown
Every step written out. Try it first by hand, then check.
Into your notebook
One click puts the circuit on a sheet of your project.
Open the calculatorOpens in the app on 1 December, with Circuit Notebook 1.0
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