A Wheatstone bridge simulator that balances to zero
Mokxi is a free online Wheatstone bridge simulator that runs in your browser, with nothing to install and no account needed. Two 10 k resistors on one side, a known 10 k and a 10 k thermistor on the other, all from 5 V, with a meter across the middle. Drag the thermistor’s temperature and watch the bridge go through balance, the way a strain gauge or a sensor bridge does.
- 455parts on the bench
- 43boards running now
- 1.00xreal time, on every board
What you can do here
In the circuit above, or in the editor it opens.
- Balance the bridge and read 0.000 V across the middle
- Find an unknown resistance from the three you know
- Change a ratio arm and watch the balance point move
- Drag the thermistor’s temperature and read the bridge as a thermometer
- Swap the meter for an op-amp and amplify the difference
- Replace the thermistor with a resistor or a potentiometer
What the running circuit shows
Two dividers, and the difference between them.
The left side is two 10 k from 5 V, so its middle sits at 2.50 V. The right side is a known 10 k over the thermistor, and the meter reads the left middle minus the right one. The bridge balances, and the meter reads zero, when Rx = R3 × R2 / R1, which here is 10 k: the thermistor’s value at exactly 25 C.
The room starts at 22.5 C, where the thermistor is about 11.2 k and the meter reads about -0.140 V. Drag it to 25 C and the meter reads 0.000 V. At 30 C it reads about +0.272 V, and at 37 C about +0.627 V. Near balance that is about 54 mV a degree, starting from a voltage that is zero when nothing has changed, which is the whole point of a bridge: the 5 V supply cancels out, and only the change is left.
To use it the textbook way, as a resistance meter, change the known arm. Make R3 4.7 k and the bridge balances near 43 C, where the thermistor has fallen to 4.7 k; read Rx off the arm that balanced it.
How the bridge is modeled
Four resistors and a meter, solved together.
Each arm is a resistor in the same nodal solve as the rest of the circuit, so the meter reads the true difference between the two middles to the millivolt. The thermistor follows the beta equation with a beta of 3950, the curve a 10 k NTC’s datasheet gives, and the meter on DC volts has a 10 megohm input, which loads a 10 k bridge by a part in a thousand.
What it leaves out: the thermistor does not heat itself with the current through it, about a quarter of a milliamp here, and has no lag, so it follows the slider at once where a real bead takes seconds. A real lab bridge uses a galvanometer or an amplifier to see microvolts near balance; this meter shows millivolts, which is plenty for a 54 mV a degree bridge but not for a strain gauge’s few millivolts in total.
Questions
Is it free?
Yes. The circuit on this page, every part in it and the editor it opens in are on the free plan, with no card.
Do I need an account?
No. The circuit runs the moment the page does, and the editor opens without one. A free account is only for saving a project to the cloud and sharing it by link.
What is the balance condition of a Wheatstone bridge?
The ratio on one side equals the ratio on the other: R1 / R2 = R3 / Rx, or Rx = R3 × R2 / R1. At balance the two middles sit at the same voltage and a meter between them reads zero, whatever the supply.
Why use a bridge instead of one divider?
A single divider reads half the supply when nothing has changed, and a small change is a small wiggle on top of that. A bridge subtracts the half away, so the meter or amplifier sees only the change, and supply noise cancels out on both sides.
Can I do a Wheatstone bridge lab without hardware?
Yes. Build the bridge on the breadboard, change the known arm until the meter reads zero, and work out the unknown. Every value is editable, so each student can get a different unknown.
More simulators
Each one opens on a circuit that is already running.
Balance a bridge
Open the circuit, drag the temperature and find zero. Nothing to install, and no account needed.