# Open-Source Magnetometer for Characterizing Magnetic Fields in Ultracold Experiments
## 3 Experimental Setup  
### Hardware  
The choice of hardware solutions has been driven by the desire to make the entire magnetometer cheap and easy to assemble while providing high performance in terms of achievable noise and resolution of the magnetic field measurement. We have taken care to make our design easy to reproduce. The mechanical assembly uses easily available commercial components like T-slotted aluminum profiles or threaded steel rods and 3D-printed parts that can be made in-house. All the 3D-printer-ready designs are available in a GitHub repository [19]. The friction between 3D-printed elements and the aluminum profile is negligible, and we achieve a smooth one-dimensional motion of the Hall sensor. In our approach, the measurements are completed after the motion of the sensor has stopped, so any vibrations or shaking that could take place during the motion itself do not noticeably influence the readout. The aluminum profile is the \"backbone\" of the setup and everything is attached to it (Figure 1), but neither the profile nor the details of the remaining components need to follow our recommendations; as long as the general approach we present is followed, the remaining hardware and software will be fully usable. The measurement range is set by the length of the T-slot profile and lengths of accordingly chosen carbon tube and the threaded rod. The range is limited by the acceptable degree of deflection of the extended carbon tube, but, if some form of a supporting structure placed close to the Hall sensor is added, the effects of deflection could be minimized. Our implementation currently offers a 50 cm range because this is sufficient to measure the field between a pair of coils in a Helmholtz configuration that are used in our laboratory for stray magnetic field compensation. However, for some long Zeeman slowers [21; 22; 23], the ability to measure magnetic field over a distance exceeding 1 m is highly beneficial. The magnetometer uses a Hall sensor attached via an adapter to a non-magnetic tube made of carbon fiber, commonly used in building model airplanes. We guide wires connecting the sensor to the microcontroller inside of it. An M8 nut embedded in the slider block enables conversion of the rotation of the threaded steel rod into the translational motion of the tube (Figure 1). The threaded rod itself is connected to the shaft of the stepper motor with a coupler. This allows precise manipulation of the sensor's position in one dimension. Smooth rotation of the threaded rod is assured by a ball bearing embedded in the end holder. We have not implemented any active position feedback that would track the location of the Hall sensor, and we rely on the microcontroller to count the steps of the stepper motor. We have implemented photosensors that define the minimum and the maximum allowed position of the sensor such that the stepper motor would always  
Figure 1: The layout of the automated magnetometer as seen from the top and from the side. Orange-colored parts are 3D-printed. The rotation of the stepper motor shaft is coupled to the threaded rod via a coupler. An M8 nut is embedded in the slider to convert the rotation of the rod into the translational motion of the carbon fiber tube, which supports the Hall sensor. The end holder uses a ball bearing to assure smooth rotation of the rod. The photosensors establish the minimum and maximum range of the motion to avoid collisions with the supporting structure in case the information about the current position of the sensor is lost. The dimensions of the pair of coils (1 mm wire, 8 \(\times\) 8 turns) used for testing of the device are shown. move within the pre-defined range. We can imagine a realistic scenario when the user fine-tunes the location of the Hall sensor by rotating the threaded rod by hand, which, effectively, would make the microcontroller lose the information about its current location. The photosensors serve as a safety switch guaranteeing that there will be no collisions with the end holder or with the stepper motor.