Developer showed how to make a compact ammeter for low direct current from Apple Watch

In Apple Watch smartwatches, starting from the Series 5 generation, there is a digital compass. It works thanks to the built-in magnetometer, which is sensitive to magnetic fields of nearby electrical networks, but for this, the sensor's sensitivity needs to be enhanced.

A coil of wire wound around the watch case copes well with the enhancement. According to the author's calculations, five turns are enough. For convenience, you can print a casing on a 3D printer, on which it is convenient to wind the wire. The author shared the STL model of the casing on GitHub. It is also important to consider that the magnetometer in the Apple Watch is not located in the center of the device, but in the lower right corner. This also affects the accuracy of measurements.

To process data and display results, you can write a special application that receives readings from the built-in magnetometer, takes into account errors and the position of the sensor. The author of the project did not develop his own application for the Apple Watch, but used the Sensor-App utility, with which you can get data from all the sensors and systems of the smartwatch.

The author also notes that in this way only the strength of the direct current can be measured, and the sensor is not fast enough for alternating current. It is noted that with a five-turn coil, the watch can measure current up to 10 mA, which is quite small. The result can be improved by increasing the number of turns and calibrating the sensor readings.