A Gauss Meter is used to learn about the strength of magnets. Presented here is the design of a low-cost
Gauss Meter for maker folks. The circuit consists of a linear Hall-Effect sensor and a standard alkaline battery. In order to make sure that the meter readings are stable over the life of the battery, a low-drop fixed voltage regulator is used which supplies a steady dc power source to the Hall-Effect sensor. First of all, note that a good-quality digital voltmeter/multimeter is essential to make the simple Gauss Meter to work.
Here is the schematic of the Gauss Meter. First one in the schematic is a compact (6F22) 9V battery (BATT). Next component LM1117-5.0 (IC1) takes +9V from the battery through the toggle switch (S1) and regulates it to +5V which the SS49E Hall-Effect sensor (IC2) will need. Final one is a “polarized” 2-pin connector (O/P1 and OP2) for the external digital voltmeter (DVM) or digital multimeter (DMM).
The Hall-Effect sensor physically is like a sort of flattened TO-92 transistor. In order to give it some mechanical robustness, you can epoxy glue flat-side of the Hall-Effect sensor on a piece of small circular plexiglass /cardboard (the sensor must be oriented so that its label side faces outwards, and can come very closer to the magnet being tested). Finally, solder its leads to a 3-core cable and link up the cable to your main circuitry.
To measure a magnet, the sensor (IC2) is held away from the magnet and note down the output voltage (usually this quiescent output voltage is around ½ vcc). Next, put the sensor against the magnet and move it until the output voltage is at its highest (south pole) or at its lowest (north pole). To measure the strength (magnetic flux density) of the magnet in Gauss, just use the formula: Magnetic Flux Density (B) = 1000 x (V1-V2) / k Gauss. Here, “V1” is the output voltage with no magnet near the sensor, and “V2” is the output voltage with a magnet near the sensor. Note that V1 should be around 2.5V, V2 will increase incase of a southpole and will decrease if it is a north pole. “k” is the typical sensitivity (mV/G) of the sensor as indicated in its datasheet.
For example, assume that you measured 2.50 Vdc for V1 and 1.35Vdc for V2.
Then B = 1000 x (2.50-1.35) / 1.80 = 638 Gauss. Here it is a north pole because the result is positive.
And, if you measured 3.50 Vdc for V2 with the same sensor
then B = 1000 x (2.50-3.50) / 1.80 = -555Gauss. Now a south pole because the result is negative.
You can also use this circuit plainly to tell you if you have a North if the output voltage (V2) decreases from V1, or a South pole if the voltage increases from V1. See how easy that is 🙂