Sep 12, 2024 19:00:00

How to use a smartwatch like the Apple Watch as an ammeter

Smartwatches such as the Apple Watch are equipped with various functions such as heart rate and electrocardiogram measurement, accelerometers, compasses, electronic payment, etc. GitHub introduces a way to use such a smartwatch as an '

ammeter '.

GitHub - jp3141/AppleWatchAmmeter: Turn your Apple Watch into an ammeter to measure DC currents
https://github.com/jp3141/AppleWatchAmmeter

A 3D-Printed Framework and Some Copper Wire Turns Your Smartwatch Into a Field-Expedient Ammeter - Hackster.io
https://www.hackster.io/news/a-3d-printed-framework-and-some-copper-wire-turns-your-smartwatch-into-a-field-expedient-ammeter-577cb394a6d4

The Apple Watch Series 5 and later and some other smartwatches are equipped with magnetometers to improve the accuracy of navigation and gesture tracking. Because this magnetometer measures magnetic fields, it can be used for other purposes in addition to simply knowing direction ( magnetic north ).

GitHub user jp3141 explains how to measure the current by winding a wire around a component attached to the Apple Watch to form a coil and changing the magnetic field it senses.

To make an ammeter with an Apple Watch or smartwatch, you need to make a 'coil holder' for winding a coil using a 3D printer or similar and fit it into the center of the main body. jp3141 distributes STL format data , a file format for 3D CAD software, for people who want to make their own parts.

The magnetic field generated by passing a current through a coil of wire varies depending on the number of turns and diameter of the coil, as well as the strength of the current. Therefore, if we know the magnetic field when no current is passing through a coil wrapped around an Apple Watch or when a constant current is passing through it, we can detect changes in the current passing through the coil.

This is what it looks like when you actually place the Apple Watch in the center of the coil holder and wrap the coil around it. If you connect a current terminal to the exposed part at the end of the wound coil, you can use it as an ammeter. In his demonstration, jp3141 used the Apple Watch compatible app '

Sensor-App ' that can measure magnetic fields, but he said that with the right knowledge you can easily create an app that performs corrections and offsets and displays current in amperes.

The ammeter that jp3141 created this time changes the magnetic field on the Z axis by about 1 μT when the current flowing through the coil changes by about 10 mA. When there is no current (0 A), the magnetic field on the Z axis is -25.62122 μT.

When a current of 1A is flowing, the magnetic field on the Z axis is 86.77788μT.

When a current of 1A flows in the reverse direction, the magnetic field on the Z axis is -138.15320μT. jp3141 said, 'There is some noise in the readings, but if you are careful, you can distinguish changes in units of 10mA (1μT).' It should be noted that only direct current (DC) can be detected, and it does not support alternating current (AC) used in household power supplies.