Tag Archives: measure

Video: Robotic arm measures magnetic fields



Stanley Lio has created a magnetometer-equipped robotic arm with three degrees of freedom to accurately measure magnetic fields.

According to HackADay’s Nick Con, the arm itself was built with standard servos and aluminum mounting hardware purchased from eBay.

“He then hooked an HMC5883L magnetometer to the robotic arm, using [Atmel’s] ATmega32U4 microcontroller (MCU) and the LUFA USB library to interface with this sensor since it has a high data rate,” Con explained.

“The results were plotted in MATLAB, a very powerful mathematical based scripting language. The plots almost perfectly match the field patterns learned in introductory classes on magnetism.”

So, what’s up for version two of the magnetometer-equipped robotic arm? Well, Stanley says he has a few tweaks in mind, including:

  • Adding extra redundant DOF
  • Having fun with math
  • Measuring positioning accuracy, precision and repeatability
  • Auto calibration using the IMU (when new servos are installed)
  • Light painting
  • Controlling the arm by real-time input devices with a camera and/or 
mouse
  • Parallel robots
  • Improving positioning accuracy

Interested in learning more? You can check out the project’s official page here.

Measuring capacitance

 with an Arduino Uno

Capacitance is typically defined as the ability of a body to store an electrical charge. More specifically, any object that can be electrically charged exhibits capacitance.

 A multimeter or multitester, also know as a VOM (Volt-Ohm Meter) can be used to measure the capacitance of a capacitor, but what if you don’t have one handy?

As it turns out, capacitance can be measured with an Atmel-based Arduino Uno (ATmega328) – sans external components and only ~20 lines of code. 

A blog post, written by Jonathan Nethercott that was recently featured on HackADay, explains how.

“[He] does an excellent job explaining a capacitance test circuit which uses a reference capacitor to calculate the unknown capacitance,” writes HackADay’s James Hobson. 

”He further explains that, with the Arduino Uno, you can remove the reference capacitor from the circuit, and simply use the stray capacitance present in the board and microcontroller, which can be calculated.”

Meaning, creating a test circuit is as simple as plugging in a capacitor to pins A0 and A2. On the software side, Nethercott’s code sense a 5V pulse to the capacitor – measuring the voltage on the other side, looping every half second and outputting the data onto a chart.

Nevertheless, as HackADay’s Hobson notes, the above-mentioned technique does require some calibration, with Jonathan measuring a known capacitor for a baseline and using the confirmed data to calculate the stray capacitance in the Arduino. 

Once accurately calibrated, users can typically achieve a resolution of approximately 1% for capacitors between 3.5pF and 225pF and around 5% for capacitors between 0.5pF and 1300pF.

Interested in learning more about how you can macgyver your Arduino Uno to measure capacitance? You can check out Jonathan Nethercott’s detailed blog post here.