Bilkent University

Department of Physics

The complete Foucault pendulum control shield schematic.

Motivation

To create a control system for the Foucault pendulum in the Bilkent University SA building. The system needed to be readily modifiable and easy to use.

The setup

The existing setup consisted of two coils buried in the floor: a thinner one used for sensing, and a thicker one used for driving. A 70-kg weight is suspended on a metal cable from the ceiling, with a permanent magnet attached on the bottom.

Parts list

• Resistors (1210):
  • 1K x3
  • 100 x3
  • 270K x1
• Capacitors (1210):
  • 100n
  • 4.7n
• 4N35 or analogous optocoupler;
• IRF640N or analogous MOSFET;
• LEDs (5mm):
  • green
  • red
• 5V Zener diode (SOD-123);
• 6A10 or analogous power diode;
• 5.08mm screw terminals x3;

The resistors R1 and R2 are current-limiting resistors for the diodes - choose the appropriate values. R3 is a current-limiting resistor for the optocoupler. R4 and R5 form a voltage divider in order to provide a 2.5V DC bias for the readings; this is needed to capture the negative part of the readings. D1 is a clamping diode to protect the input of the Arduino, and C1 is a filtering capacitor.

D2 is a flyback diode for the driving coil. R6 is a pull-down resistor. R7 and C2 form a low-pass filter in order to pull the base of the optocoupler's transistor low.

Some words of caution

In our case, with 7V power supply, the driving coil draws up to 3A of current. The setup needs to be rated to handle that, in particular the tracks on the PCB. Currently the setup is also somewhat susceptible to noise, e.g. from mains lines, so this needs to be put into consideration.

About the standalone version

The standalone (Arduino-less) board was supposed to be the next iteration of this project, in order to make it cheaper and easier operate. It was, however, neither reviewed nor even prototyped, so all bets are off when it comes to working.

Authors

Cemal Yalabik designed the circuit; Furkan Gönül wrote the code; Said Sattarov designed the PCB; with special thanks to Sadettin Karateke.

Licence

This work is licenced under CC-BY-SA 4.0