Wheatstone Bridge Calculator
A Wheatstone Bridge is essentially two voltage dividers connected in parallel, with their outputs compared to determine a difference. This configuration is used for precise resistance measurement and sensing applications like temperature or strain measurement.
How it works
The bridge consists of four resistors in a diamond arrangement:
- Static divider: R1 (top-left) and R3 (bottom-left)
- Variable divider: R2 (top-right) and R4 (bottom-right)
The output voltage is the difference between the two divider midpoints:
Vout = Vvariable - Vstatic
Where:
- Vstatic = Vin x R3 / (R1 + R3)
- Vvariable = Vin x R4 / (R2 + R4)
When R1/R3 = R2/R4, the bridge is balanced and Vout is zero. Any change in one resistor (for example an NTC thermistor responding to temperature) creates a measurable differential voltage.
Applications
- Temperature measurement using NTC or platinum RTD sensors
- Strain gauge measurement
- Pressure sensing
- Any application requiring precise detection of small resistance changes
Worked example
A bridge with R1 = R2 = R3 = 10,000 ohms and an NTC thermistor as R4, powered by 3.3V. As the thermistor temperature changes, the bridge output shifts:
| Temperature (C) | R4 (ohms) | Vout (mV) |
|---|---|---|
| 0 | 32,650 | +880 |
| 20 | 12,490 | +183 |
| 25 | 10,000 | 0 |
| 40 | 5,325 | -258 |
| 60 | 2,488 | -558 |
| 80 | 1,256 | -764 |
| 100 | 677 | -879 |
The output is non-linear but provides good sensitivity across the working range. An ADC with 12-bit resolution on a 3.3V reference gives approximately 0.8 mV per count, well within the range needed for sub-degree accuracy in solar thermal monitoring.